Content-type: text/html Man page of cc

cc

Section: User Commands (1)
Index Return to Main Contents
 

NAME

cc - C compiler  

SYNOPSIS

cc [option...] file...


 

Default Options:

cc -newc -assume aligned_objects -assume math_errno -cpp -call_shared -double -fprm n -fptm n -g0 -I/usr/include -inline manual -intrinsics -member_alignment -no_fp_reorder -no_misalign -O1 -oldcomment -p0 -no_pg -preempt_symbol -signed -archgeneric -std0 -tune generic -weak_volatile -writable_strings


 

OPTIONS

Options described in this section are divided into the following categories: Compiler selection options Language mode options Overall compiler behavior options Compiler diagnostic controls options C preprocessor options Linker or loader options Optimization options Feedback-directed optimization options Source-code debugging options Program profiling options Data alignment options Data volatility options C language options Rounding-mode options (IEEE floating-point) Stack-handling and pointer-handling options IEEE floating-point support options Compiler development options (not generally used)
 

Compiler Selection Options

This is the default. Invokes the compiler with a set of optimization settings that are slightly different from those associated with -newc. These settings are consistent with the cc -migrate settings for versions of the DEC OSF/1 operating system that preceded DIGITAL UNIX Version 4.0. This option is provided for backwards compatibility only, and its use is strongly discouraged. Invokes the older, ucode-based implementation of the C compiler that was the default for versions of the DEC OSF/1 operating system preceding DIGITAL UNIX Version 4.0. It can be invoked only after the OSFOBSOLETE subset has been installed.

See cc(1old) for details on the -newc, -migrate, and -oldc options and their effects.
 

Language Mode Options

The language mode options are mutually exclusive. When more than one such option appears on the command line, the last one listed will take effect. The default is -std0. Selects the relaxed ANSI language mode. Enforces the ANSI C standard, but allows some common programming practices disallowed by the standard.

This option does not restrict the Tru64 UNIX name space (for example, the names defined in system header files). To restrict that name space so that only ANSI C reserved names are visible from the ANSI C header files, use the _ANSI_C_SOURCE macro. See standards(5) for more details.
This option causes the macro __STDC_ to be defined to 0. Selects the K & R language mode. This is the default. Enforces the K & R programming style, with certain ANSI extensions in areas where the K & R behavior is undefined or ambiguous. In general, -std0 compiles most pre-ANSI C programs and produces expected results. The -std0 option causes the __STDC__ macro to be undefined. Selects the strict ANSI language mode. Strictly enforces the ANSI C standard and all its prohibitions (such as those that apply to the handling of void types, the definition of lvalues in expressions, the mixing of integrals and pointers, and the modification of rvalues).
This option does not restrict the Tru64 UNIX name space (for example, the names defined in system header files). To restrict that name space so that only ANSI C reserved names are visible from the ANSI C header files, use the _ANSI_C_SOURCE macro. See standards(5) for more details.
This option causes the macro __STDC_ to be defined to 1. Note that this option also affects linker-defined symbols. See ld(1) for more information.
This option turns on ANSI aliasing rules (-ansi_alias option). Selects the Microsoft language mode, which provides some compatibility with the Microsoft Visual C compiler. Although this option does not provide full compatibility, it can be useful as a porting aid. It provides the following extensions. Except for these extensions, the -ms option is equivalent to -std. Allow a declaration of an unnamed structure within another structure. You can reference all members of the inner structure as members of the named outer structure. This is similar to the C++ treatment of nested unions lacking a name, but extended to both structures and unions. For example:
struct {
   struct {
      int a;
      int b;
   };  /*No name here */
   int c; }d; /* d.a, d.b, and d.c are valid member names. */ Allow duplicate typedef declarations. For example:
typedef int typedefname; typedef int typedefname; Allow typedef declarations that are redeclared to a compatible type. For example:
typedef enum {a,b,c} typedefname; typedef enum {d,e,f} typedefname; Allow declaration of a structure with a trailing incomplete array. This is useful if you are dealing with counted arrays, where the first element of the structure is used to hold a count of the array elements, the second element is an array of data, and the structure is always allocated dynamically. The sizeof operator treats the incomplete array as having a length of zero. For example:
struct {
   int a;
   int b[]; }s; Allow a static function declaration in block scope (that is, inside another function). For example:
f() {
    static int a(int b); } Allow & to produce an lvalue expression in certain cases. For example:
int *a, *b;
   f() {
       &*a=b; } Allow integers and pointers to be compared without a cast. For example:
int *a,b; f() { if (a==b)
   b=1; } Treat the char type as either signed char or unsigned char, depending of the default in effect. For example, a pointer to char can be assigned to a pointer to signed char, assuming that the -signed option is in effect:
signed char *a; Suppress warning messages for declarations that contain two semicolons; that is, allow completely empty declarations at file scope. For example:
int a;; Suppress warning messages for declarations that contain a variable name but no type. For example:
b;
This is assigned type int. Ignore any extra comma at the end of the last enumerator in an enumeration declaration. For example:
enum E {a, b, c,}; /* Ignore the comma after "c". */ Allow typedef declarations that have a type specifier but no identifier name declaring the new type. For example:
typedef struct { int a; }; Suppress warning messages when one of the following unsupported Microsoft pragmas is encountered:
#pragma code_seg #pragma optimize #pragma warning
Selects the K & R language mode. This option is equivalent to -std0. Selects the K & R language mode. This option is equivalent to -std0. Selects the VAX C language mode. This is similar to -std (relaxed ANSI mode) but extends the language semantics in ways that are incompatible with ANSI C. It provides close compatibility with the vaxc compiler.
 

Overall Compiler Behavior Options

Causes the compiler to recognize additional keywords. The following options are available: The default compilation mode on OpenVMS systems includes recognition of the following keywords that are not available on Tru64 UNIX except in -vaxc mode: _align, globaldef, globalref, globalvalue, noshare, readonly, variant_struct, and variant_union. This option causes these keywords to be recognized. It may help in porting applications from OpenVMS systems. Cause the compiler to recognize the restrict keyword (from the C9X review draft). Specifies which version of the Alpha architecture to generate instructions for. All Alpha processors implement a core set of instructions and, in some cases, the following extensions: BWX (byte/word-manipulation extension), MVI (multimedia extension), FIX (square root and floating-point convert extension), and CIX (count extension). (The Alpha Architecture Reference Manual describes the extensions in detail.)

The option specified by the -arch option determines which instructions the compiler can generate: Generate instructions that are appropriate for all Alpha processors. This option is the default. Generate instructions for the processor that the compiler is running on (for example, EV6 instructions on an EV6 processor). Generate instructions for the EV4 processor (21064, 20164A, 21066, and 21068 chips) and EV5 processor (some 21164 chips). (Note that chip number 21164 is used for both EV5 and EV56 processors.)
Applications compiled with this option will not incur any emulation overhead on any Alpha processor. Generate instructions for EV56 processors (some 21164 chips).
This option permits the compiler to generate any EV4 instruction, plus any instructions contained in the BWX extension.
Applications compiled with this option may incur emulation overhead on EV4 and EV5 processors. Generate instructions for EV6 processors (21264 chips).
This option permits the compiler to generate any EV6 instruction, plus any instructions contained in the following extensions: BWX, MVI, FIX, and CIX.
Applications compiled with this option may incur emulation overhead on EV4, EV5, EV56, and PCA56 processors. Generate instructions for PCA56 processors (21164PC chips).
This option permits the compiler to generate any EV4 instruction, plus any instructions contained in the BWX and MVI extensions.
Applications compiled with this option may incur emulation overhead on EV4, EV5, and EV56 processors.
A program compiled with any of the options will run on any Alpha processor. Beginning with DIGITAL UNIX V4.0 and continuing with subsequent versions, the operating system kernel includes an instruction emulator. This capability allows any Alpha chip to execute and produce correct results from Alpha instructions--even if the some of the instructions are not implemented on the chip. Applications using emulated instructions will run correctly, but may incur significant emulation overhead at run time.
The psrinfo -v command can be used to determine which type of processor is installed on any given Alpha system.
Note the following differences between the -arch evx and -tune evx options (where x designates a specific processor): -arch evx implies -tune evx, but -tune evx does not imply -arch evx. -arch evx can generate unguarded evx-specific instructions. If you run that application on a pre-evx processor, those instructions may get emulated (and emulated instructions can be up to 1000 times slower than actual instructions). -tune evx can generate evx-specific instructions, but those are always amask-guarded. That expands the code size but avoids instruction emulation. If you want the best performance possible on an evx processor and are not concerned about performance on earlier processors, the best choice would be -arch evx (which implies -tune evx). If you want good performance on an evx processor but also want the application to run reasonably fast on earlier processors, the best choice would probably be -tune evx. Suppresses the loading phase of the compilation and forces the creation of an object file. When syntactic or semantic errors are detected by the compiler's front end, invokes the editor defined by the environment variable EDITOR (or vi if EDITOR is undefined). Two files are opened for editing: the error message file, which indicates the location of the error, and the source file. When you exit from the editor, the compilation is restarted.
The n argument specifies the number of times a compilation can be interrupted in this way. If no number is specified, the compile-edit-compile cycle repeats indefinitely until all errors are corrected. The -edit0 option turns off this feature. To abort the cycle, you must press Ctrl-C while the process is in the compilation phase (that is, while it is not in the editor).
When compiling on a character-based terminal, the compile job has to be in the foreground for this option to take effect. When compiling on a workstation, this option takes effect whether it is in the foreground or background. Sets a limit on the number of error-level diagnostics that the compiler will emit. The default is 30. Specifies a file that is to be included before the first line in a source file is actually compiled. This enables users to develope include files containing sets of pragmas that control a particular aspect of a compilation (for example, optimizations or diagnostics). Causes the macro __STDC_VERSION__ to be passed to the preprocessor and enables recognition of the digraph forms of various operators. Note that the -isoc94 option has no influence on -stdn options and vice versa. Sets the nesting-level limit for include files. The default is 50. Includes the generated machine code in the listing file. By default, machine code is not listed. To produce the listing file, you must also specify -source_listing. Suppresses creation of an object file. By default, an object module file is created with the same name as that of the first source file of a compilation unit and with the .o file extension.
Use the -noobject option when you need only a listing of a program or when you want the compiler to check a source file for errors.
This option is not available when you use the -oldc option. Names the final output file output. Ensures that the compiler's assumptions about pointer sizes and data alignments are not in conflict with the default values that were in effect when the system libraries were created.
The keywords for the -protect_headers option are as follows: Enables the protect headers feature. This is the default if the file being compiled is a C source file. Disables the protect headers feature. This is the default if the file being compiled is a non-C source file. Cancels any previous -protect_headers options and places the compiler's default behavior in effect.
If more than one -protect_headers option appears on the command line, only the last one is applied. See protect_headers_setup(8) for details. Compiles the specified source files and generates symbolic assembly language output in corresponding files suffixed with .s. Specifies one or more items to be included in the listing file. When specifying multiple keywords, separate them by commas and no intervening blanks. To use any of the -show keywords, you must also specify the -source_listing option.
The keywords for the -show option are as follows: Turns off all show options. Turns on all show options. Places final macro expansions in the program listing. When you specify expansion, the number printed in the margin indicates the maximum depth of macro substitutions that occur on each line. Produces header lines at the top of each page of listing. Places contents of header files in program listing. Places source program statements in program listing. Places compile-time performance statistics in the program listing.
If you specify -source_listing but do not specify -show keywords, the compiler includes header lines and source statements in the program listing (-show header,source). Produces a source program listing file with the same name as the source file and with a .lis file extension. You must specify this qualifier to get a listing. The default is to not produce a listing file. Prints the compilation phases as they execute with their arguments and their input and output files. Prints resource usage in the C-shell time format. Prints the macros defined at the start of the compilation (for -newc and -migrate only). Prints the version of the compiler driver and, when the -oldc option is specified, the versions of all passes in the same format as the what command.
 

Compiler Diagnostic Controls Options

Performs compile-time code checking. With this option, the compiler checks for code that exhibits nonportable behavior, represents a possible unintended code sequence, or possibly affects operation of the program because of a quiet change in the ANSI C Standard. Some of these checks have traditionally been associated with the lint utility.

The -check option is equivalent to -msg_enable level5. The cc driver converts -check into -msg_enable level5 (the -v option notifies you of this transformation). Causes the compiler to dump, to stdout, all messages enabled by any given cc command line. The compiler then exits, without doing a compilation. Provides users with the ability to control the diagnostic messages issued by the compiler. The message output can be tuned in groups (based on message level or message group) or individually (based on the message ID strings enclosed in parentheses at the end of message text strings).
The -msg_actiontype option has eight different forms, each resulting in a different action that changes the status, severity, or frequency that will be applied to the messages identified by the msg_list argument. The following message-control options are supported: Enable a specific message or group of messages. Disable a specific message or group of messages. (Note that messages with error or fatal severity cannot be disabled; only warning and informational messages can be disabled.) Always emit the messages identified by the msg_list argument. Emit the identified messages only once. Change the identified messages to be fatal, compilation-ending errors. Change the identified messages to be warnings. (Note that error- or fatal-severity messages cannot be changed to warning-severity messages.) Change the identified messages to be informational messages. (Note that error- or fatal-severity messages cannot be changed to informational-severity messages.) Change the identified messages to be error messages. (Note that fatal-severity messages cannot be changed to error-severity messages.)
The msg_list argument to the -msg_actiontype option is a comma-separated list of one or more message levels, message groups, or message IDs. Enabling a message level also enables all lower levels, and disabling a level also disables all higher levels. For example, disabling level 3 messages disables levels 3 - 6. Operations other than enabling or disabling apply only to the specified (or default) level, not to lower levels.
The following message levels and message groups are supported:
Message Levels: Very important messages that are enabled by default. Level 0 messages cannot be disabled as a class (level0), but individual level 0 messages can be disabled if they are warning- or informational-severity messages. (Error- or fatal-severity messages cannot be disabled.)
Messages at this level correspond to messages covered by pragma nostandard. These include all messages that should be displayed for code in header files. Important messages, but less important than level 0 messages. These messages are not displayed if pragma nostandard is active. Level 1 is the default for DIGITAL UNIX releases prior to V4.0E. Moderately important messages. Level 2 is the default for the DIGITAL UNIX V4.0E and later versions. Less important messages. (The -w0 option enables level 3 messages.) Useful messages associated with the -check and -portable options. Less useful -check and -portable messages than the messages associated with level 4. The -check option is equivalent to -msg_enable level5. All messages, including all messages not in any of the lower levels. Disabling level 6 messages does not affect the lower-level messages; it affects only the messages added by level 6.
Message Groups: Messages reporting code or practices that may have unintended consequences on 64-bit architectures. Messages reporting unusual or inefficient data alignment. Messages reporting the use of C features that would be invalid or have a different meaning if compiled by a C++ compiler. Messages reporting code or practices that, although correct and perhaps portable, are sometimes considered ill-advised because they can be confusing or fragile to maintain (for example, assignment as the test expression in an if statement). Messages reporting the use of obsolete features, features that were accepted by early C compilers but were subsequently removed from the language. Messages reporting the use of non-ANSI C features. Messages reporting the use of features that are valid in ANSI C, but which are identified in the standard as being obsolescent and likely to be removed from the language in a future version of the standard. Messages reporting assignments and/or casts that may cause overflow or other loss of data significance. Messages reporting code that might result in poor run-time performance. Messages reporting the use of language extensions or other constructs that might not be portable to other compilers or platforms. -msg_enable portable is equivalent to -portable. Messages reporting questionable or non-portable use of preprocessing constructs. Messages reporting questionable coding practices. Similar to check, but messages in this group are more likely to indicate a programming error, not just a non-robust style. Messages relating to function return values. Messages reporting expressions, declarations, and code paths that are not used. Directs the compiler to issue diagnostics for certain constructs that may not be portable to other compilers or platforms. -portable is equivalent to -msg_enable portable. Suppresses certain warning- and informational-level diagnostic messages that are inappropriate for system header files. The suppressed messages relate to non-portable constructs in header files whose pathnames are prefixed by string directory.
The default is -SD/usr/include.
Specifying -SD without a directory string cancels the effect of any previous -SD options on the command line (including the default, -SD/usr/include). It also disables the -protect_headers feature's suppression of diagnostic messages by defining the macro __DECC_EMPTY_SD_OPTION. (The -protect-headers feature provides message suppression in the file __DECC_include_prologue.h.) Produces longer error and warning messages. Messages in this form may give the user more hints about why the compilation failed. Controls the display of messages as well as the actions that occur as a result of the messages. The value of n can be one of the following: Displays all levels of compiler messages (warning, error, fatal, and informational). This is the default. Suppresses warning and informational messages and displays error and fatal messages. This is equivalent to specifying -w. If the compiler encounters an error that generates a warning-level diagnostic message, the compiler displays the message and then aborts. Does not print warning messages. However, when warnings occur, exits with nonzero status. Causes the compiler to produce warning messages when a function is called that is not declared with a full prototype. This checking is more strict than required by ANSI C.
 

C Preprocessor Options

Passes all comments directly to the preprocessor output, except comments on preprocessor directive lines. Determines whether to call the C macro preprocessor on C and assembly source files before compiling.

-cpp is the default. Defines the name as if with a #define statement. If no definition is given, the name is defined as 1. Runs only the C macro preprocessor on the files and sends the result to the standard output device. Specifies a search path for header files whose names do not indicate a specific directory path (that is, whose names do not begin with a /). The actual search path depends upon the form of the #include directive used for the file: If the #include "filename" form of the directive is used, the C macro preprocessor searches for the file first in the directory in which it found the file that contains the directive, then in the search path indicated by the -I option, and finally in the standard directory, /usr/include. If the #include <filename> form of the directive is used, the preprocessor searches for the file first in the search path indicated by the -I option, and then in the standard directory, /usr/include.
You can specify multiple iterations of the -I[dir] option in the cc command line; each instance of the -[dir] option appends locations to the previously established -I[dir] search path. If no dir is specified in any instance of the -I[dir] option, the C macro preprocessor never searches the standard directory, /usr/include, for header files.
The -nocurrent_include option can also modify the search path. Outputs a set of make dependency rules to standard output for each source file on the command line (and suppresses compilation). The make dependencies include all of the header files upon which each source file depends. The make targets are the object files for those source files. The output lines are indented to show header file nesting. Requests dependency files from the preprocessor (and linker if it is also run). It does not suppress compilation like the -M option. This option is passed directly to the preprocessor and linker. For more information, see cpp(1) and ld(1). Changes the behavior of the #include "filename" directive to not search the source file's directory for filename. This option causes the #include "filename" directives to behave like #include <filename> directives. This option allows makefiles to control the search order for header files by using -I options. Directs the preprocessor to delete comments (replacing them with nothing at all). This allows traditional token concatenation.
This is the default in -std0 mode. In -std and -std1 mode, the default is to replace comments with a single space. Runs only the C preprocessor and puts the result for each .c or .s source file in a corresponding .i file. The .i file has no #line_number preprocessor directives in it. Extracts prototype declarations for function definitions and puts them in a .H suffixed file. The suboption i includes identifiers in the prototype, and the suboption s generates prototypes for static functions as well. Directs the preprocessor to use single quotes in __FILE__ expansions instead of double quotes. See cpp(1) for details. Removes any macro definition of name at the start of the compilation. name could have been defined with a -D option or predefined by the compiler. If no name is specified or if name is not defined, the -U option is ignored. (To display a list of predefined macros, use the -v option.)
 

Linker or Loader Options

Produces a dynamic executable file that uses shareable objects during run time. This is the default. The loader uses shareable objects to resolve undefined symbols. The run-time loader (/sbin/loader) is invoked to bring in all required shareable objects and to resolve any symbols that remained undefined during static link time. Passes the -compress option to the compilation phase (if the -c option is present) or passes the -compress_r option to ld (if the -r option is present). Use of this option causes the output object file to be produced in compressed object file format, resulting in a substantially smaller object file. Runs the procedure rearranger, cord, on the resulting file after linking. The rearrangement is done to reduce the cache conflicts associated with accessing the program's text. The output of cord is left in the file specified by the -o output option or a.out by default. At least one -feedback file must be specified. See prof(1) for information on creating feedback files. Used in conjunction with -call_shared to request strict dependency testing for the executable file produced. Executable files built in this manner can be executed only if the shared libraries that they use were not modified after the executable was built. Causes any unresolved symbols matching pattern to be ignored. Such symbols are not displayed and are not treated as errors or warnings. You can enter this option multiple times on a command line. The patterns use shell wildcard characters (?, *, [, ]). The wildcard characters must be properly quoted to prevent them from being expanded by the shell. For more information, see sh(1). Makes the procedure represented by the symbol into a termination routine. A termination routine is a routine that is called without an argument when either the file that contains the routine is unloaded or the program that contains the routine exits. Makes the procedure represented by the symbol into an initialization routine. An initialization routine is a routine that is called without an argument when either the file that contains the routine is loaded or the program that contains the routine is started. Directs the linker to read the contents of file filename as if the contents had been supplied on the ld command line.

Inside file filename, lines ending with \ are treated as continuation lines, and lines starting with # are treated as comment lines and ignored. The -v option can be used to display the expansion of files specified in a -input file. The files can be nested up to 20 levels. Prevents the linker from using archive libraries to resolve symbols. This option is used in conjunction with -call_shared. The -no_archive option is position sensitive; it affects only those options and variables that follow it on the command line. This option can also be used more than once on the command line. Directs the linker to produce a static executable. The output object created by the linker will not use any shared objects during execution. Produce dynamic shareable objects. The loader will produce a shareable object that other dynamic executables can use at run time.
The following options are used with -shared: Checks the location of this shared object's segments and make sure they stay out of the way of other object's segments in the location_file. Multiple instances of this option are allowed. Creates an rpath record containing the specified path string. The path string is a colon-separated list of directories that is meaningful only when creating an executable with shared linkage. If an item in the path supplied to -rpath is of the form $VARNAME or ${VARNAME}, the linker interprets it as an environment variable.
Additional rpath directories found in shared objects on the link command line are appended to path. Duplicate entries are excluded. The loader uses the rpath record to search for shared libraries at run time. Establishes the version identifier (or identifiers) associated with a shared library. The string version-string is either a single version identifier or a colon-separated list of version identifiers. No restrictions are placed on the names of version identifiers; however, it is highly recommended that UNIX directory naming conventions be followed.
If a shared library is built with this option, any executable built against it will record a dependency on the specified version or, if a list of version identifiers is specified, the rightmost version specified in the list. If a shared library is built with a list of version identifiers, the loader will allow any executable to run that has a shared library dependency on any of the listed versions. Sets DT_SONAME for a shared object. The name can be a single component name (for example, libc.a), a full pathname (starting with a slash), or a relative pathname (containing a slash). The default DT_SONAME used for shared objects is the filename component of the output file name. Specify the output file name using the -o option as described previously. Registers the location of this shared object's segments and makes sure they stay out of the way of others in the location_file. Location_file is updated if it is writable. Directs the linker to use the threadsafe version of any library specified with the -l option when linking programs. This option also tells the linker to include the POSIX 1003.1c-conformant DECthreads interfaces in libpthread when linking the program. Directs the linker to load the executable file in the lower 31-bit addressable virtual address range. The -T and -D options to the ld command can also be used, respectively, to ensure that the text and data segments addresses are loaded into low memory.
The -taso option, however, in addition to setting default addresses for text and data segments, also causes shared libraries linked outside the 31-bit address space to be appropriately relocated by the loader. If you specify -taso and also specify text and data segment addresses with -T and -D, those addresses override the -taso default addresses. The -taso option can be helpful when porting programs that assume address values can be stored in 32-bit variables (that is, programs that assume that pointers are the same length as int variables). Directs the linker to use the threadsafe version of any library specified with the -l option when linking programs. This option also tells the linker to include the POSIX 1003.4a Draft 4 conformant DECthreads interfaces. It is supported only for compatibility with earlier releases of Tru64 UNIX. New designs should use the -pthread option.
 

Optimization Options

Directs the compiler to assume the ANSI C aliasing rules, and thus allows the optimizer to be more aggressive in its optimizations. The -noansi_alias option turns off ANSI C aliasing rules.

The aliasing rules are explained in Section 3.3, paragraphs 20 and 25 of the ANSI C Standard, reprinted as follows:
``An object shall have its stored value accessed only by an lvalue that has one of the following types: The declared type of the object, A qualified version of the declared type of the object, A type that is the signed or unsigned type corresponding to the declared type of the object, A type that is the signed or unsigned type corresponding to a qualified version of the declared type of the object, An aggregate or union type that includes one of the aforementioned types among its members (including, recursively, a member of a subaggregate or contained union), or A character type.''
If your program does not access the same data through pointers that have different types (and for this purpose, signed and qualified versions of an otherwise same type are considered to be the same type), then assuming ANSI C aliasing rules allows the compiler to generate better optimized code.
If your program does access the same data through pointers that have different types (for example, by a ``pointer to int'' and a ``pointer to float''), you must not allow the compiler to assume ANSI C aliasing rules because these rules can result in the generation of incorrect code.
The default is to assume no ANSI C aliasing rules when compiling with the -vaxc, -std, or -std0 option. The default is -ansi_alias when compiling with the -std1 option.
The -noansi_alias option turns off ANSI C aliasing rules.
The -[no]ansi_alias option is not available when you use the -oldc option. Tells the compiler whether the source code follows all ANSI rules about arguments, that is, whether the type of an argument matches the type of the parameter in the called function or whether a function prototype is present so the compiler can automatically perform the expected type conversion.
Specifying -no_ansi_args means that the argument type may not match the expected parameter type. This option is important, for example, when the caller passes a parameter of type long and the called routine expects an int. The -no_ansi_args option forces the compiler to generate argument cleaning code to convert the argument to the appropriate type. Except when the -std1 option is specified, -no_ansi_args is the default. Note that it is safe to specify -ansi_args if you use ANSI-style function prototypes at all call sites.
Specifying -ansi_args means that your code meets the ANSI C requirements, so no special argument cleaning code is generated. This is a performance gain. When -std1 is specified, -ansi_args is the default. Specifies the assumption that all array parameters are restricted. In the following code, for example, only b will be considered a restricted pointer when this option is not specified, even though for all other purposes parameters a and b have identical type:
extern int foo(char * a, char b[]);
When this option is specified, both a and b are treated as restricted pointers. Controls the compiler's assumption about a program's dependence on the setting of errno by math library routines: By default (-assume math_errno), the compiler assumes that the program might interrogate errno after any call to a math libarry routine that is capable of setting errno. The definition of the ANSI C math library allows programs to depend on this behavior, which unfortunately restricts optimization because this causes most math functions to be treated as having side effects. Specifying -assume nomath_errno instructs the compiler to assume that the program does not look at the value of errno after calls to math functions. This assumption allows the compiler to reorder or combine computations to improve the performance of those math functions that it recognizes as intrinsic functions. In practice, robust floating-point code seldom relies on errno to detect domain or range errors, so -assume nomath_errno can often be safely used to improve performance. Specifies the assumption that all pointer parameters are restricted. Specifies the assumption that all pointers are restricted.
The -assume norestricted_pointers option disables the __restrict keyword from all pointers. This can help detect inappropriate use of __restrict. If the code works correctly at high optimization with __restrict turned off, but breaks with it turned on, it is likely that the compiler encountered a pointer that was restricted in error. Restricted pointers are an assertion by the programmer to aid optimization; the compiler cannot detect erroneous assertions. Specifies that no occurrences of the address-of operator (&) are being applied outside the current compilation unit to extern variables that are declared inside the current compilation unit. Making this assertion allows the compiler to perform better optimizations.
This option is often suitable for use with the -ifo option, which presents a group of source files to the compiler as a single compilation unit. Provides a single method for turning on a collection of optimizations for increased performance.
Note that the -fast option can produce different results for floating-point arithmetic and math functions, although most programs are not sensitive to these differences.
The -fast option defines the following compiler options and symbols to improve run-time performance. You can adjust the optimizations by specifying the negation of any given option. Directs the compiler to assume the ANSI C aliasing rules, and thus allows the optimizer to be more aggressive in its optimizations.
See the description of this option elsewhere in this reference page for more detailed information about this operation. Tells the compiler that the source code follows all ANSI rules about arguments; that is, whether the type of an argument matches the type of the parameter in the called function, or whether a function prototype is present so the compiler can automatically perform the expected type conversion.
See the description of this option elsewhere in this reference page for more detailed information about this operation. Allows the compiler to reorder or combine computations to improve the performance of those math functions that it recognizes as intrinsic functions.
See the description of this option elsewhere in this reference page for more detailed information about this operation. Specifies that any short accessed through a pointer is naturally aligned. This generates the fastest code, but can silently generate the wrong results if any of the short objects cross a quadword boundary.
See the description of this option elsewhere in this reference page for more detailed information about this operation. This option affects the compilation of a number of system header files, causing them to compile #pragma intrinsic directives for certain functions that they declare. The exact functions affected may vary depending on the language mode and other macro definitions. See the header files math.h, stdio.h, stdlib.h, string.h, and strings.h for details. The exact effect of each #pragma intrinsic varies by function, by optimization options, and by other compile-time options. The basic effect is to inform the compiler that the function specified in the pragma is the one by that name whose behavior is known to the compiler (that is, it is a standard C or commonly-used library function rather than a user-written external function). This gives the compiler license to perform additional checks on the usage of the function and issue diagnostics, and to optimize and/or rewrite calls to it based on the compiler's understanding of what the function does. Some possible optimizations include generating complete inline code, generating partial inline code with calls to one or more different functions, or just using characteristics of the function to move the call site or avoid some of the overhead triggered by an external call. This option affects the compilation of stdio.h in two ways: Whenever the header file would otherwise define getc and putc as preprocessor macros expanding into code to access the _cnt and _ptr members of the referenced FILE object directly, instead these macros are defined to invoke inlined static functions defined in the header file. The use of an inlined static function instead of a simple macro prevents the argument from being evaluated more than once (so arguments containing side effects do not cause a problem), and the function generally will produce better code because it uses local declarations to avoid aliasing assumptions that the compiler has to make when analyzing the traditional macro expansions of getc and putc. Note that getc and putc are not expanded inline when i/o locking is required, as is normally the case for reentrant or thread-safe compilations. If -D_INTRINSICS was also specified, making printf and fprintf intrinsic functions, then certain of the low-level runtime support routines that may be called for special cases of format strings are defined as inline static functions in the header file, avoiding external calls to these routines in libc. Causes the /usr/include/math.h file to redefine the names of certain common math routines, including sqrt and exp, so that faster but slightly less accurate functions are used. The fast math routines do not support IEEE exceptional behavior. Tells the compiler that it is not necessary to promote expressions of type float to type double.
See the description of this option elsewhere in this reference page for more detailed information about this operation. Allows floating-point operations to be reordered during optimization.
See the description of this option elsewhere in this reference page for more detailed information about this operation. Performs inter-file optimizations.
See the description of this option elsewhere in this reference page for more detailed information about this operation. Controls whether the compiler recognizes certain functions as intrinsic functions.
See the description of this option elsewhere in this reference page for more detailed information about this operation. Sets the optimization level.
See the description of this option elsewhere in this reference page for more detailed information about this operation. Makes string literals read-only for improved performance.
See the description of this option elsewhere in this reference page for more detailed information about this operation. Specifies the name of a feedback file (produced by prof after running a pixie version of the program). The feedback file contains information that the compiler can use when performing optimizations.
You can also use a feedback file as input to the cord utility, using -feedback and the -cord options to link the program. Specifies whether certain code transformations that affect floating-point operations are allowed. These changes can affect the accuracy of the program's results.
The -no_fp_reorder option, the default, directs the compiler to use only certain scalar rules for calculations. This setting can prevent some optimizations. The -fp_reorder option frees the compiler to reorder floating-point operations based on algebraic identities (inverses, associativity, and distribution). For instance, this allows the compiler to move divide operations outside of loops, thus improving performance.
If you specify -fp_reorder and the compiler reorders code to improve performance, the results can differ from the default, for example, due to the way intermediate results are rounded. However, the -fp_reorder results are not categorically less accurate than those gained by the default. Provide improved optimization (inter-file optimization) and code generation across file boundaries that would not be possible if the files were compiled separately.
When you specify -ifo on the command line in conjunction with a series of file specifications, the compiler does not concatenate each of the specified source files. Instead, each file is treated separately for purposes of parsing, except that the compiler will issue diagnostics about conflicting external declarations and function definitions that occur in different files. For purposes of code generation, the compiler treats the files as one application. The default is to not provide inter-file optimization. Specifies whether to provide inline expansion of functions. This is the default for -O2, -O3, -O4. The -no_inline option disables this optimization.
When choosing calls to expand inline, the compiler also considers the function size, how often the call is executed, how many registers the inline expansion will require, and other factors.
You can specify one of the following as the keyword to control inlining: No inlining is done, even if requested by a #pragma inline preprocessor directive. This is the default when compiling with the -O0 option. Inlines only those function calls explicitly requested for inlining by a #pragma inline directive. This is the default when compiling with the -O1 option. Inlines all of the function calls in the manual category, plus any additional calls that the compiler determines would improve run-time performance without significantly increasing the size of the program. This is the default when compiling with the -O2 or -O3 option. Inlines all of the function calls in the manual category, plus any additional calls that the compiler determines would improve run-time performance, even where it may significantly increase the size of the program. Inlines every call that can be inlined while still generating correct code. Recursive routines, however, will not cause an infinite loop at compile time.
For optimization level 0 (-O0), the -inline option is ignored and no inlining is done. The #pragma noinline preprocessor directive can also prevent inlining of any function. The -intrinsics option causes the compiler to recognize intrinsic functions wherever it can automatically, based only on name and call signature. Unlike -D_INTRINSICS, this option can treat library function calls as intrinsic even when the appropriate header file is not included. Any function declaration or call site (in the case of implicit declaration) with a name matching the name of an intrinsic function is examined to see if its parameters and return result are consistent with the intrinsic function of that name. If so, calls are treated as being intrinsic. If not, a diagnostic is issued and calls are treated as ordinary external function calls.
When the compiler identifies a function as an intrinsic function, it is then free to make code optimizations (transformations) based on what it knows about the operations performed by the standardized version of that function--given an optimization level (-On) that enables the intrinsic treatment of that particular function.
The optimization level determines which functions can be treated as intrinsics: No intrinsic functions. The -intrinsics option has no effect at this optimization level. Memory and string functions: alloca, bcopy, bzero, memcpy, memmove, memset, strcpy, strlen
Math functions: abs, fabs, labs, atan, atan2, atan2f, atand, atand2, atanf, ceil, ceilf, cos, cosd, cosf, floor, floorf, sin, sind, sinf. fprintf, printf, snprintf, sprintf acos, acosf, asin, asinf, cosh,coshf, exp, expf, log, log10, log10f, logf, log2, pow, powf, sqrt, sqrtf, sinh, sinhf, tan, tand, tanf, tanh.
The effects of the various optimization levels are cumulative; for example, -fast causes the functions at the -02 (or -O) and -O3 optimization levels to be treated as intrinsics--in addition to the intrinsic function treatment that is triggered by -fast itself.
The -intrinsics option is in effect by default. To disable the default, specify the -no_intrinsics option. To disable the intrinsic treatment of individual functions, specify the function names in a pragma function directive in either your source code or a file associated with a -FI option (``file include'' option).
Although -intrinsics is the default (and it will generally treat calls to [f]printf as intrinsic), in order to have the low-level support routines for intrinsic [f]printf inlined, the compilation must include and also specify both -D_INTRINSICS and -D_INLINE_INTRINSICS on the command line. Enables the compiler to process parallel decomposition pragmas (directives) in C source code. It also triggers the link phase to link with the appropriate thread and compiler support libraries that are needed to run the generated multiprocessor code.
A correctly coded program that makes use of the parallel decomposition pragmas can be compiled either with or without -mp. With -mp, the pragmas cause the program to run in several concurrent threads that may execute in a significantly shorter elapsed time on a Tru64 UNIX multiprocessor system. Without -mp, the compiler will ignore the pragmas and the program will run sequentially as a normal C program. Determines the level of optimization. The following table lists the types of optimizations that can be performed at each level:

LevelOptimization

-O0None
-O1 Local optimizations and recognition of common subexpressions. Global optimizations, including code motion, strength reduction and test replacement, split lifetime analysis, and code scheduling.
-O2, -O Inline expansion of static procedures. Additional global optimizations that improve speed (at the cost of extra code size), such as integer multiplication and division expansion (using shifts), loop unrolling, and code replication to eliminate branches.
-O3Inline expansion of global procedures.
-O4 Software pipelining using dependency analysis, vectorization of some loops on 8-bit and 16-bit data (char and short), and insertion of NOP instructions to improve scheduling.

If your application will be built into a shared library, avoid using the -O3 and -O4 options, because these levels may inhibit the ability to preempt symbols. Also, benchmarking is recommended to determine if -O4 is better than -O3 for your particular application, as this is not always true. Performs code optimization after linking, including nop (no operation) removal, .lita removal, and reallocation of common symbols. This option also positions the $gp register so that the maximum number of addresses fall in the $gp-accessible window. The -om option is supported only for programs compiled with the -non_shared option. The following options can be passed directly to -om by using the -WL compiler option: Removes unused .lita entries after optimization, and then compresses the .lita section. Removes dead code (unreachable instructions) generated after applying optimizations. The .lita section is not compressed by this option. Sets the size threshold of ``common'' symbols. Every ``common'' symbol whose size is less than or equal to num will be allocated close to each other. This option can be used to improve the probability that the symbol can be accessed directly from the $gp register. (Normally, om tries to collect all ``common'' symbols together, not just symbols that conform to certain size constraints.) Uses the pixie-produced information in file.Counts and file.Addrs to reorganize the instructions to reduce cache thrashing. Turns off instruction scheduling. Turns off alignment of labels. Normally, the -om option will quadword align the targets of all branches to improve loop performance. Splits frequently accessed routines into ``hot'' and ``cold'' code segments, and stores these segments in different parts of the image. The hot segments are the most frequently executed parts of the code, as determined by feedback data produced by a representative run of the program. The hot segments are stored near other parts of the program that are also executed frequently. In this way, the most frequently executed parts of the program are compacted in a way that makes them more likely to fit into the cache. This speeds up the execution time of that code.
For additional information on om, send email to [email protected], specifying help on the subject line. Then, follow the instructions in the reply you receive to obtain report number 94/1. Supports symbol preemption on a module-by-module basis. During optimization, inlining is performed only on functions within a single compilation unit. This is the default in the following cases: At optimization levels -O3 and -O4. When -ifo is used. When the compilation is proceeding directly to an a.out executable file, that is, when none of the following options are specified on the command line: -c, -r, or -shared.
In all other cases, -preempt_symbol is the default. Preserves full symbol preemption; that is, supports symbol preemption on a symbol-by-symbol basis within a module as well as between modules. Restricts the optimizer so that calls to extern functions are ineligible for inline replacement.
The default taken for a compilation is either -preempt_symbol or -preempt_module. See the description of the -preempt_module option for details on the conditions that determine which option is taken as the default. Specifies that speculation may occur anywhere in the executable image.
Speculation is a compiler optimization that causes the hardware to begin executing an operation before it determines that the flow of control will actually reach that operation. If the flow of control does reach that operation, the result will be available sooner than it would have been without speculative execution. If the flow of control does not reach that operation, the result will simply be ignored.
Since unsuccessful speculative operations can generate exceptions, all exceptions are dismissed when any module that contributes to the application is compiled with the -speculate all option (though floating-point instructions specifying software completion are still handled normally). This optimization is therefore inappropriate for codes that use any form of local exception handling (or is linked to other codes that do). Specifies that speculation is allowed only in the code in the source module that is being compiled.
A module compiled with -speculate by_routine cannot use any form of local exception handling, but can be linked with other modules that do. The run-time system checks each exception to see if it occurred in a speculative routine. It dismisses exceptions from routines that are speculatively executed, but signals exceptions from other routines. (Note, though, that floating-pointing instructions specifying software completion [/S] are still given normal exception handling.) As a result, you should use the -speculate by_routine option only for modules that are known to be error-free and that do not depend on fault and trap handling. If code compiled speculatively incurs a lot of exceptions, it may result in an overall performance loss. If this is so, you should discontinue use of this feature.
The -speculate by_routine option yields somewhat slower execution than the -speculate all option, but does not restrict trap and fault handling in other modules with which it is linked. Instructs the optimizer to tune the application for a specific version of the Alpha hardware. This will not prevent the application from running correctly on other versions of Alpha but it may run more slowly than generically-tuned code on those versions.
The option argument can be one of the following, which selects instruction tuning appropriate for the listed processor(s): All Alpha processors. This is the default. The processor on which the code is compiled. The 21064, 21064A, and 21068 processors. The 21164 processor. (Both EV5 and EV56 are numbered 21164.) The 21264 processor.
See also the -arch option for an explanation of the differences between -tune and -arch. Controls the loop-unrolling optimization (available only at levels -O2 and higher). -unroll n allows the compiler to unroll loops up to n times. -unroll 1 disables the optimization. -unroll 0 (the default) allows the compiler to decide what is best.
 

Feedback-directed Optimization Options

Generates accurate profile information to be used with -feedback optimizations, as follows: Compile the source code with the -gen_feedback option. Run pixie on the executable file. Execute the pixie version of the program to generate execution statistics on the program. Use prof to create a feedback file from the execution statistics. Recompile the program with the -feedback option and optimization level -O1 or above. This provides the compiler with execution information that the compiler can use to improve certain optimizations.

This option is not available when you use the -oldc option. Generates an executable image that has profiling code added to it. Using this option is equivalent to running the pixie(5) command on an existing image. The pixie-instrumented file is called a.out (or as specified with the -o option). The uninstrumented file is given an extension of .non_pixie. See also the descriptions of the -prof_use_om_feedback, -prof_dir, and -pids options. Uses profiling feedback to improve compiler optimization. Using this option is equivalent to using the prof(1) command to produce a feedback file, and then using the cc -feedback command to recompile the program.
To use the -prof_use_feedback option, first compile your program with the -prof_gen and -gen_feedback options and then run the program to generate the needed profiling data. Uses profiling feedback to rearrange the resulting image to reduce cache conflicts of the program text. This option uses the -om postlink optimizer, and is equivalent to using the -om -WL,-om_ireorg_feedback options. If the -pids option is also specified, this option merges the .Counts performance data files using the prof -pixie -merge command.
To use the -prof_use_om_feedback option, first compile your program with the -prof_gen option and then run the program to generate the profiling data. Specifies a location to which the profiling data files (.Counts and .Addrs) are written. Use this option in conjunction with the -prof_gen option and the -prof_use_feedback or -prof_use_om_feedback option to specify a location for the profiling data files. If you do not specify this option, the profiling files are written to the current directory.
Specifying the -prof_dir option also enables the -pids option. [Disables] or enables the addition of the process-id to the filename of the basic block counts file (.Counts). This facilitates collecting information from multiple invocations of the pixie output file. Unless the -prof_dir option is specified, the default is -no_pids.
 

Source-code Debugging Options

Produces symbol table information for debugging. When no value is specified for n, the compiler produces symbol table information for full symbolic debugging and suppresses optimizations that limit full symbolic debugging (same as -g2).

The value of n can be one of the following (-g is the same as -g2): Produces only enough symbol table information for linking. Names and addresses of external symbols, and the addresses and basic layout of the stack-frame are available. Profiling tools work, but the names of local procedures, source lines, and source file names are not available. The debugger allows procedure traceback and all instruction-level commands. However, line-oriented commands do not work. No symbol types are available, and the names of stack-frame and static variables are not available. All optimizations are supported. Produces limited symbol table information. Profiling and debugging tools provide line numbers, source file names, and the names of local procedures, when appropriate. Line-oriented debugging commands work, but symbol types and the names of stack-frame variables are not available. Most profiling tools work to their fullest ability, but some advanced Atom tools may provide more information at higher debug levels. All optimizations are supported. Produces symbol table information for full symbolic debugging and suppress some optimizations. Symbol types and stack-frame variables names are available. Optimization is suppressed (-g2 implies -O0). Produces symbol table information for fully optimized code. This level of debugging supplies the same information as -g2, but it also allows all compiler optimizations. As a result, some of the correlation is lost between the source code and the executable program.
 

Program Profiling Options

Determines the level of profiling. The -p option prepares for profiling by periodically sampling the value of the program counter. This option affects linking only, so that when linking occurs, the standard run-time startup routine is replaced by the profiling run-time startup routine (mcrt0.o) and the level 1 profiling library (libprof1.a) is searched. When you use the -p option together with either the -pthread option or the -threads option, the profiling library libprof1_r.a is used.

When profiling begins, the startup routine calls monstartup (see monitor(3)) and produces, in file mon.out, execution-profiling data for use with the postprocessor prof(1).
The value n can be one of the following: Do not permit any profiling. This is the default. If linking occurs, the standard run-time startup routine (crt0.o) is used, and no profiling library is searched. Same as -p. Turns gprof profiling on or off when compiling and linking the file immediately following this option. The gprof profiler produces a call graph showing the execution of a C program.
When this option is turned on, the standard run-time startup routine is replaced by the gcrt0.o routine. Programs that are linked with the -pg option and then run will produce, in file gmon.out, a dynamic call graph and profile. You then run gprof on the gmon.out file to display the output. When you use the -pg option together with either the -pthread option or the -threads option, the profiling library libprof1_r.a is used.
For more information, see the gprof(1) reference page.
 

Data Alignment Options

Controls the alignment assumptions for code generated for indirect load and store instructions.

The -assume aligned_objects option causes the compiler to assume that a dereferenced object's alignment matches or exceeds the alignment indicated by the pointer to the object. On Alpha systems, dereferencing a pointer to a longword- or quadword-aligned object is more efficient than dereferencing a pointer to a byte- or word-aligned object. Therefore, when the compiler assumes that a pointer object of an aligned pointer type does point to an aligned object, it can generate better code for pointer dereferences of aligned pointer types.
The -assume noaligned_objects option causes the compiler to generate longer code sequences to perform indirect load and store operations in order to avoid hardware alignment faults for arbitrarily aligned addresses. Although the -assume noaligned_objects option may generate less efficient code than -assume aligned_objects, by avoiding hardware alignment faults, it speeds the execution of programs that reference unaligned data.
The -assume aligned_objects option is the default. The compiler assumes that the alignment of pointers meets or exceeds that of the objects to which they point. The following rules apply: A pointer of type short points to objects that are at least short-aligned. A pointer of type int points to objects that are at least int-aligned. A pointer of type struct points to objects that have an alignment of struct (that is, the alignment of the strictest member alignment, or byte alignment if you have specified #pragma nomember_alignment for struct).
If your module breaks one of these rules, you must use the -assume noaligned_objects option to compile the module; otherwise, your program may get alignment faults during execution, which will degrade performance.
The -assume aligned_objects and -assume noaligned_objects options can be used in the same cc command, allowing you to turn this option on and off as needed by individual source files.
The -assume aligned_objects and -assume noaligned_objects are not available when you use the -oldc option. However, the -misalign option is a synonym for -assume noaligned_objects and the -no_misalign option is a synonym for -assume aligned_objects. Controls the compiler's assumptions about the alignment of short types accessed through a pointer.
Specifying -assume trusted_short_alignment indicates that the compiler should assume any short accessed through a pointer is naturally aligned. This generates the fastest code, but can silently generate the wrong results if any of the short objects cross a quadword boundary.
Specifying -assume notrusted_short_alignment tells the compiler that short objects may not be naturally aligned. The compiler generates slightly larger (and slower) code that will give the correct result, regardless of the actual alignment of the data. This is the default.
Note that -assume notrusted_short_alignment does not override the __unaligned type qualifier, the -misalign option, or the -assume noaligned_objects option. Controls the alignment assumptions for code generated for indirect load and store instructions.
The -misalign option is a synonym for -assume noaligned_objects and the -no_misalign option is a synonym for -assume aligned_objects. The -assume [no]aligned_objects option is discussed earlier in this reference page. Directs the compiler to byte-align data structure members (with the exception of bit-field members).
By default, data structure members are aligned on natural boundaries (that is, on the next boundary appropriate to the type of the member) instead of the next byte. For example, an int variable member is aligned on the next longword boundary, and a short variable member is aligned on the next word boundary.
Any use of the #pragma member_alignment, #pragma nomember_alignment, or #pragma pack directives within the source code overrides the setting established by this option.
The use of the -nomember_alignment option can cause conflicts between the compiler's assumptions about data layouts and the default values that were in effect when the system libraries were created. See protect_headers_setup(8) for details on how to avoid this conflict. Aligns structure members based on the integer n, where n can be 1, 2, 4, or 8. This option specifies packing so that each structure member after the first is stored on n-byte boundaries. When you specify the -Zp option without an n value, structure members are packed on 1-byte boundaries.
The use of the -Zpn option (where n!=8) can cause conflicts between the compiler's assumptions about data layouts and the default values that were in effect when the system libraries were created. See protect_headers_setup(8) for details on how to avoid this conflict.
 

Data Volatility Options

Affects the generation of code for assignments to objects that are less than or equal to 16 bits in size (for instance char, short) that have been declared as volatile. The generated code includes a load-locked instruction for the enclosing longword or quadword, an insertion of the new value of the object, and a store-conditional instruction for the enclosing longword or quadword. By using this locked instruction sequence for byte and word stores, the -strong_volatile option allows byte and word access of data at byte granularity. This means that assignments to adjacent volatile small objects by different threads in a multithreaded program will not cause one of the objects to receive an incorrect value. Affects the generation of code for assignments to objects that are less than or equal to 16 bits in size (for instance char, short) that have been declared as volatile. The generated code includes a read of the enclosing longword or quadword, an insertion of the new value of the object, and a store of the enclosing longword or quadword. This is the default.

The -weak_volatile option does not generate locked instructions for this sequence. This allows byte or word access to memory-like I/O devices for which larger accesses will not cause read or write side effects. Because the sequence does not access byte or word data independently directly in memory (that is, ensure byte granularity), adjacent volatile data can be corrupted when such byte or word accesses are performed in a multithreaded environment (for example, two volatile shorts stored in a longword and accessed asynchronously).
 

C Language Options

Promotes expressions of type float to double. This is the default when -std0 is used. Prevents the compiler from promoting expressions of type float to type double. This is the default except in -std0 mode. Causes the compiler to assign floating-point constants the type float (rather than double) if their values can be represented in single precision. This option is not available in -std1 mode. Allows the compiler to assume that string literals are read-only. This may improve application performance. This option overrides -writable_strings, which is the default.

Attempting to modify string literals when -readonly_strings is specified may yield unpredictable results (for example, a segmentation fault). Causes all char declarations to have the same representation and range of values as signed char declarations. This is used to override a previous -unsigned option. This is the default. Causes all char declarations to have the same representation and range of values as unsigned char declarations. Prints warnings for all lines that may require the <varargs.h> macros. Causes all variables to be treated as volatile. Causes all string literals to be writable. This is the default.
This option overrides -readonly_strings.
 

Stack-handling and Pointer-handling Options

Forces all uninitialized stack variables to be initialized with 0xfff58005fff58005. When this value is used as a floating-point variable, it is treated as a floating-point NaN and causes a floating-point trap. When it is used as a pointer, an address or segmentation violation usually occurs. Causes the compiler to respect the #pragma pointer_size directives, which control the size of pointers. These directives are ignored otherwise.

Pointers are 64 bits by default. This option, when used in conjuction with the pointer_size pragmas, allows applications to use 32-bit pointers. Images built with this option must be linked with the -xtaso or -taso option in order to run correctly. See the Programmer's Guide for information on #pragma pointer_size. Directs the compiler to allocate 32-bit pointers by default. You can still use 64-bit pointers, but only by the use of pragmas. The -xtaso_short option also implies -xtaso; that is, -xtaso_short also causes the compiler to respect the pointer_size pragmas.
The use of the -xtaso_short option can cause conflicts between the compiler's assumptions about pointer sizes and data layouts and the default values that were in effect when the system libraries were created. See protect_headers_setup(8) for details on how to avoid this conflict. Makes all procedures in the source file use $fp (register 15) as the frame pointer.
 

IEEE Floating-point Support Options

Specifies chopped rounding mode (round toward zero). Dynamically sets rounding mode for IEEE floating-point instructions. The dynamic rounding mode is determined from the contents of the floating-point control register and can be changed or read at execution time by a call to write_rnd(3) or read_rnd(3). If you specify -fprm d, the IEEE floating-point rounding mode defaults to round to nearest. Specifies normal rounding mode (unbiased round to nearest). This is the default. Specifies round toward minus infinity mode. Generates instructions that do not trigger floating-point underflow or inexact trapping modes. Any floating point overflow, divide-by-zero, or invalid operation will unconditionally generate a trap. The -fptm n option is the default. Generates traps on floating-point underflow as well as overflow, divide-by-zero, and invalid operation. Ensure support of all portable features of the IEEE Standard for Binary Floating-Point Arithmetic (ANSI/IEEE Std 754-1985), including the treatment of denormalized numbers, NaNs, and infinities and the handling of error cases. This option also sets the _IEEE_FP C preprocessor macro.

If your program must use IEEE signaling features that are not portable across different IEEE implementations, see the ieee(3) reference page for a discussion of how to access them under the Tru64 UNIX operating system. Ensures that any trap (such as floating-point overflow) is reported to have occurred in the procedure or guarded scope that caused the trap. Any trap occurring outside that scope is not reported to have occurred in the procedure or guarded scope, with the exception of well-defined trapb instructions following jsr instructions.
 

Compiler Development Options (Not Generally Used)

Halts compiling after the pass specified by the character c, producing an intermediate file for the next pass. The c character can be one of the following: [ fjusmoca ]. It selects the compiler pass in the same way as the -t option. If this option is used, the symbol table file produced and used by the passes is given the name of the last component of the source file with the suffix changed to .T, and the file is always retained after the compilation is halted. Passes the argument, or arguments (argi), to the compiler pass, or passes (c[c...]). Each c character can be one of the following: [ pfjusdqmocablyz ]. The c selects the compiler pass in the same way as the -t option.

The options from the set -t[hpfjusmocablyzrntLCD], -hpath, and -Bstring select a name to use for a particular pass, startup routine, or standard library. These arguments are processed from left to right, so their order is significant. When the -B option is encountered, the selection of names takes place using the last -h and -t options. Therefore, the -B option is always required when using -h or -t. Sets of these options can be used to select any combination of names.

All -B options must be preceded by -p options. The -p option provides the location of startup routines and the profiling library.

Use the -t [hpfjusmocablyzrntLCD] suboptions to select the names. The names selected are those designated by the characters following the -t option, according to the following table:


NameCharacter

h (see note following table)
gemc_ccp, f
as0a
as1b
ldl
cordz
[m]crt0.or
libprof1.an
omL
pixieC
profD

If the character h is in the -t argument, a directory is added to the list of directories to be used in searching for header files. The name of this directory has the form $COMP_TARGET_ROOT/usr/include/string. This directory is to contain the header files for the string release of the compiler. The standard directory is still searched. Use path instead of the directory where the name is normally found. Append string to all names specified by the -t option. If no -t option has been processed before the -B, the -t option is assumed to be hpfjusmocablyzrntL. This list designates all names.

If no -t argument has been processed before the -B, then a -Bstring is passed to the loader to use with its -lx arguments.

Invoking the compiler with a name of the form ccstring has the same effect as using a -Bstring option on the command line.
 

DESCRIPTION

The cc command invokes the C compiler. It accepts any of the following file arguments: Arguments whose names end with .c are assumed to be C source programs. They are compiled, and each object program is left in a file whose name consists of the last component of the source with .o substituted for .c. The .o file is deleted only when a single source program is compiled and loaded all at once. Arguments whose names end with .s are assumed to be symbolic assembly language source programs. They are assembled, producing a .o file. Arguments whose names end with .i are assumed to be C source files after being processed by the C preprocessor. Arguments whose names do not end with .c, .s, or .i are assumed to be either C-compatible object files, typically produced by an earlier cc run, or libraries of C-compatible routines.

The cc command accepts options that are specific to either the cc command or the ld command (linker). When the compiler recognizes position-sensitive linker options (-L, -all, -exclude, -exported_symbol, -hidden, -hidden_symbol, -kl, -l, -none, -non_hidden, and -no_archive), it maintains their relative order for the linker. This reference page describes the options that are specific to the cc command. See ld(1) for a description of the linker options.

All of the input files, plus the results of the compilations, are loaded in the order given to produce an executable program with the default name a.out. The compiler can produce object files in extended COFF format (the normal result). It can also produce object files in symbolic assembly language format when invoked with the -S option.

When the compiler is invoked, it defines C preprocessor macros that identify the language of the input files and the environments in which the code can run. You can reference these macros in #ifdef statements to isolate code that applies to a particular language or environment. The C preprocessor macros are listed in the following table. Note that the type of standards you apply and the type of source file determine which macros are defined.


MacroSource File Type-std option

__DECC.c
__DECC_VER.c -std0, -std, -std1
LANGUAGE_C.c-std0
__LANGUAGE_C__.c -std0, -std, -std1
unix.c, .s-std0
__unix__.c, .s -std0, -std, -std1
__osf__.c, .s -std0, -std, -std1
__alpha.c, .s -std0, -std, -std1
_LONGLONG.c, .s -std0, -std, -std1
SYSTYPE_BSD.c, .s-std0
_SYSTYPE_BSD.c, .s -std0, -std, -std1
LANGUAGE_ASSEMBLY.s -std0, -std, -std1
__LANGUAGE_ASSEMBLY__ .s -std0, -std, -std1

You can explicitly define macros with the -D option to control which functions are declared in header files and to obtain standards conformance checking. See standards(5) for a list of the macro names and details on the function declarations and standards conformance checking associated with the various macros.

While the -D option controls which functions are declared in header files, the -stdn options control how strictly the declarations conform to the ANSI C standard. For strict ISO C and ANSI C conformance, the compiler command line must include the -std1 option.

To facilitate setting default compiler options, you can create an optional configuration file named comp.config or an environment variable named DEC_CC: The comp.config file allows system administrators to establish a set of compilation options that are applied to compilations on a system-wide basis. The compiler options in comp.config must be specified on a single line, and the comp.config file should be stored in the compiler target directory, /usr/lib/cmplrs/cc. The DEC_CC environment variable allows DEC C users to establish a set of compilation options that are applied to subsequent compilation on a per-user basis.

The DEC_CC environment variable can contain two distinct sets of compilation options separated by a single vertical bar (|). The options before the vertical bar are known as prologue options and the options after the bar are know as epilogue options.
The DEC_CC environment variable can begin or end with a vertical bar, or have no vertical bar at all. If no vertical bar is present, the options are treated as prologue options by default. Any vertical bar found after the first vertical bar is treated as whitespace and a warning is issued.

Compiler options are processed in the following order during a compilation: comp.config options DEC_CC prologue options command line options DEC_CC epilogue options

If -v is specified on the command line, the contents of DEC_CC and comp.config, if present, are displayed.
 

EXAMPLES

To compile the file helloworld.c using the compiler's defaults use the following command: cc helloworld.c

Because no output file is named in the command line, the result of the compilation is written to the executable file named a.out. In this example, the -v option displays the name of each compilation pass--and its arguments--as it executes. cc -v helloworld.c /usr/lib/cmplrs/cc/gemc_cc -D__LANGUAGE_C__ -D__unix__ -D__osf__ -D__alpha -D_SYSTYPE_BSD -D_LONGLONG -DLANGUAGE_C -Dunix -DSYSTYPE_BSD -I/usr/include -v -preempt_module -intrinsics -g0 -O2 -std0 -o helloworld.o helloworld.c

These macros are in effect at the start of the compilation. ----- ------ --- -- ------ -- --- ----- -- --- ------------

-D__DECC -D__osf__ -D__PRAGMA_ENVIRONMENT -D_LONGLONG -D__X_FLOAT=0 -D__DATE__="Sep 2 1998" -D__DECC_VER=50890008 -DLANGUAGE_C -DSYSTYPE_BSD -D_SYSTYPE_BSD -D__DECC_MODE_COMMON -D__ALPHA -D__IEEE_FLOAT -D__unix__ -D__TIME__="10:37:01" -D__Alpha_AXP -D__INITIAL_POINTER_SIZE=0 -Dunix -D__LANGUAGE_C__ -D__alpha /usr/lib/cmplrs/cc/gemc_cc: 0.01u 0.01s 0:00 50% 0+8k 0+2io 0pf+0w 8stk+1048mem /usr/lib/cmplrs/cc/ld -g0 -O1 -call_shared /usr/lib/cmplrs/cc/crt0.o helloworld.o -lc /usr/lib/cmplrs/cc/ld: 0.01u 0.01s 0:00 16% 0+9k 0+12io 0pf+0w 9stk+1192mem


 

ENVIRONMENT VARIABLES

The following environment variables can affect compiler operation: Provides a default value for locale variables that are not set. If any of these variables contains an invalid setting, the compiler behaves as if none were set. If set to a non-empty string, this variable overrides values in all locale variables, including LANG. Determines the locale for the interpretation of sequences of bytes of text data as characters (for example, single- as opposed to multi-byte characters in arguments and input files). Determines the locale used for diagnostic messages. Determines the locale of message catalogs for the processing of LC_MESSAGES. Provides a pathname that overrides the default directory for temporary files, if any.

For more information on these environment variables, see i18n_intro(5) and l10n_intro(5).
 

FILES

Input file Object file Loaded output Temporary Compiler configuration file (optional) C macro preprocessor DEC C compiler Post-link optimizer Symbolic to binary assembly language translator Binary assembly language assembler and reorganizer Run-time startup Startup for prof profiling Startup for gprof profiling Standard library, see intro(3) Level 1 profiling library Reentrant level 1 profiling library for code compiled with -pthread or -threads Standard directory for header files Interface between prof and cord Procedure-rearranger File produced for analysis by prof File produced for analysis by gprof
 

SEE ALSO

as(1), atom(1), cc(1old), c89(1), cord(1), dbx(1), ftoc(1), gprof(1), hiprof(5), ieee(3), ladebug(1), ld(1), monitor(3), pixie(5), prof(1), protect_headers_setup(8), standards(5), third(5), what(1)

ANSI X3.159-1989

B. W. Kernighan and D. M. Ritchie, The C Programming Language

B. W. Kernighan, Programming in C -- a tutorial

D. M. Ritchie, C Reference Manual

Programmer's Guide

Assembly Language Programmer's Guide

DEC C Language Reference Manual


 

Index

NAME
SYNOPSIS
Default Options:
OPTIONS
Compiler Selection Options
Language Mode Options
Overall Compiler Behavior Options
Compiler Diagnostic Controls Options
C Preprocessor Options
Linker or Loader Options
Optimization Options
Feedback-directed Optimization Options
Source-code Debugging Options
Program Profiling Options
Data Alignment Options
Data Volatility Options
C Language Options
Stack-handling and Pointer-handling Options
IEEE Floating-point Support Options
Compiler Development Options (Not Generally Used)
DESCRIPTION
EXAMPLES
ENVIRONMENT VARIABLES
FILES
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 02:42:57 GMT, October 02, 2010