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Compaq C

Compaq C
User's Guide for OpenVMS Systems

Contents

Index

Text-Module Form

For the text-module (nonportable) form of inclusion, the name can only be an identifier. It, therefore, has no associated file type.

The identifier is used as a module name to search the following:

The text libraries named on the command line with /LIBRARY qualifiers, in left-to-right order.
The following list of text libraries in the order shown (unless the /INCLUDE_DIRECTORY qualifier contains an empty string, in which case no further text libraries are searched):
DECC$TEXT_LIBRARY
SYS$LIBRARY:DECC$RTLDEF.TLB
SYS$LIBRARY:SYS$STARLET_C.TLB

The default for this qualifer is /NOINCLUDE_DIRECTORY.

/INSTRUCTION_SET=[NO]FLOATING_POINT (ALPHA ONLY)

The /INSTRUCTION_SET=NOFLOATING_POINT qualifier suppresses the generation of floating-point instructions for integer operations.

The default is /INSTRUCTION_SET=FLOATING_POINT.

/L_DOUBLE_SIZE=option (ALPHA ONLY)

Determines how the compiler interprets the long double type. The qualifier options are 64 and 128.

Specifying /L_DOUBLE_SIZE=64 treats all long double references as G_FLOAT, D_FLOAT, or T_FLOAT, depending on the value of the /FLOAT qualifier.

Specifying /L_DOUBLE_SIZE=128 treats all long double references as X_FLOAT.

The default is /L_DOUBLE_SIZE=128.

/LIBRARY

Indicates that the associated input file is a library containing modules of Compaq C source text. If the library specification does not include a file extension, the CC command line assumes the .TLB default type. You must join the /LIBRARY qualifier with a file specification in a compilation unit using a plus sign (+); you cannot place the qualifier at other places on the CC command line. No matter where you place the /LIBRARY qualifier in a compilation unit, all files in the unit may make reference to modules within that library. Consider the following example:

$ CC ONE + TWO + THREE/LIBRARY[Return]

Files ONE.C and TWO.C can contain references to modules in THREE.TLB. Consider the following example:

$ CC ONE + TWO + THREE/LIBRARY, FOUR[Return]

The file FOUR.C cannot contain references to modules in THREE.TLB since FOUR.C is located in a separate compilation unit separated by a comma. The placement of the library file specification does not matter. The following command lines are equivalent:

$ CC THREE/LIBRARY + ONE + TWO[Return] $ CC ONE + THREE/LIBRARY + TWO[Return] $ CC ONE + TWO + THREE/LIBRARY[Return]

/[NO]LINE_DIRECTIVES

Governs whether or not #line directives appear in preprocess output files.

The default is /LINE_DIRECTIVES.

/[NO]LIST[=file-spec]

Produces a source program listing. You must specify this qualifier to get a listing. None of the other qualifiers use /LIST by default.

By default, /LIST creates a listing file with the same name as the source file and with a file extension of .LIS. If you include a file specification with the /LIST qualifier, the compiler uses that specification to name the listing file.

In interactive mode, the default is /NOLIST. In batch mode, the default is /LIST. See the descriptions of the qualifiers /[NO]MACHINE_CODE, and /SHOW for related information. (For example, to suppress compiler messages to the terminal or to a batch log file, use the /SHOW=NOTERMINAL qualifier.)

/[NO]MACHINE_CODE[=option]

Lists the generated machine code in the listing file. To produce the listing file, you must also specify /LIST.

On OpenVMS VAX systems, several formats exist to list machine code. Table 1-10 describes the /MACHINE_CODE qualifier options.

Table 1-10 /MACHINE_CODE Qualifier Options (VAX ONLY)
Option Usage

AFTER Causes the lines of machine code produced during compilation to print after all the source code in the listing.

BEFORE Causes lines of machine code produced during compilation to print before any source code in the listing.

INTERSPERSED Produces a listing consisting of lines of source code followed by the corresponding lines of machine code. This is the default option.

Table 1-10 /MACHINE_CODE Qualifier Options *(VAX ONLY)*
Option	Usage
AFTER	Causes the lines of machine code produced during compilation to print after all the source code in the listing.
BEFORE	Causes lines of machine code produced during compilation to print before any source code in the listing.
INTERSPERSED	Produces a listing consisting of lines of source code followed by the corresponding lines of machine code. This is the default option.

On OpenVMS Alpha sytems, the format of the generated machine code listing is similar to what you would get using the AFTER keyword on OpenVMS VAX systems.

The default is /NOMACHINE_CODE.

/[NO]MEMBER_ALIGNMENT

Controls whether the compiler naturally aligns data structure members. Natural alignment means that data structure members are aligned on the next boundary appropriate to the type of the member, rather than on the next byte. For instance, a long variable member is aligned on the next longword boundary; a short variable member is aligned on the next word boundary.

Any use of the #pragma member_alignment or #pragma nomember_alignment directives within the source code overrides the setting established by this qualifier. Specifying /NOMEMBER_ALIGNMENT causes data structure members to be byte-aligned (with the exception of bit-field members).

On OpenVMS Alpha systems, the default is /MEMBER_ALIGNMENT.

On OpenVMS VAX systems, the default is /NOMEMBER_ALIGNMENT.

See the description of #pragma [no]member_alignment in Section 5.4.11.

/[NO]MMS_DEPENDENCIES[=(option[,...])]

Directs the compiler to produce a dependency file. Dependency files list all source files and included files for each object module. The dependency file format is:

object_file_name :<tab><source file name>) object_file_name :<tab><full path to first include file>) object_file_name :<tab><full path to second include file>)

Table 1-11 shows the /MMS_DEPENDENCIES qualifier options.

Table 1-11 /MMS_DEPENDENCIES Qualifier Options
Option Usage

FILE[=filespec] Specifies where to save the dependency file. The default file extension for a dependency file is .mms . Other than using this different default extension, /MMS_DEPENDENCY uses the same procedure that the /OBJECT and /LIST qualifiers do for determining the name of the output file.

[NO]SYSTEM_INCLUDE_FILES Specifies whether or not to include dependency information about system include files (those included with #include < filename> .) If omitted, this option defaults to including dependency information about system include files.

**Table 1-11 /MMS_DEPENDENCIES Qualifier Options**
Option	Usage
FILE[=filespec]	Specifies where to save the dependency file. The default file extension for a dependency file is `.mms` . Other than using this different default extension, /MMS_DEPENDENCY uses the same procedure that the /OBJECT and /LIST qualifiers do for determining the name of the output file.
[NO]SYSTEM_INCLUDE_FILES	Specifies whether or not to include dependency information about system include files (those included with `#include < filename>` .) If omitted, this option defaults to including dependency information about system include files.

The default is /NOMMS_DEPENDENCY.

/NAMES=(option1,option2)

Option1 converts all definitions and references of external symbols and psects to the case specified. Table 1-12 lists the option1 case values.

Table 1-12 /NAMES Qualifier Option1 Values
Option Usage

UPPERCASE Converts to uppercase.

LOWERCASE Converts to lowercase.

AS_IS Leaves the case as specified in the source.

**Table 1-12 /NAMES Qualifier Option1 Values**
Option	Usage
UPPERCASE	Converts to uppercase.
LOWERCASE	Converts to lowercase.
AS_IS	Leaves the case as specified in the source.

Option2 controls whether or not external names greater than 31 characters get truncated or shortened. Table 1-13 lists the option2 values.

Table 1-13 /NAMES Qualifier Option2 Values
Option Usage

/NAMES=TRUNCATED (default) Truncates long external names.

/NAMES=SHORTENED Shortens long external names.
A shortened name consists of the first 23 characters of the name followed by a 7-character Cyclic Redundancy Check (CRC) computed by looking at the full name, and then a "$".

**Table 1-13 /NAMES Qualifier Option2 Values**
Option	Usage
/NAMES=TRUNCATED (default)	Truncates long external names.
/NAMES=SHORTENED	Shortens long external names. A shortened name consists of the first 23 characters of the name followed by a 7-character Cyclic Redundancy Check (CRC) computed by looking at the full name, and then a "$".

The default is /NAMES=(UPPERCASE,TRUNCATED), which provides the same conversion-to-uppercase behavior as VAX C, and truncates the name to 31 characters.

Notes

On OpenVMS VAX systems, the /NAMES qualifier does not affect the names of the $CODE and $DATA psects.

On OpenVMS Alpha systems, the /NAMES qualifier does not affect the names of the $ABS$, $BSS$, $CODE$, $DATA$, $LINK$, $LITERAL$, and $READONLY$ psects.

Specifying /NAMES=SHORTENED turns on the /REPOSITORY qualifier.

/NESTED_INCLUDE_DIRECTORY[=option]

Controls the first step in the compiler's search algorithm for finding files that are included using the quoted form of the #include preprocessing directive:

#include "file-spec"

Table 1-14 describes the /NESTED_INCLUDE_DIRECTORY qualifier options.

Table 1-14 /NESTED_INCLUDE_DIRECTORY Qualifier Options
Option Usage

PRIMARY_FILE Directs the compiler to search the default file type for headers using the context of the primary source file (the .C file). This means that just the file type (".h" or ".") is used for the default file-spec, but the chain of "related file-specs" used to maintain the sticky defaults for processing the next top-level source file is also applied when searching for the include file. This most closely matches the behavior of VAX C.

INCLUDE_FILE Directs the compiler to first search the directory of the source file containing the #include directive. If the file to be included is not found, the compiler continues searching by following normal inclusion rules.

NONE Directs the compiler to skip the first step of processing #include " file.h" directives. The compiler starts its search for the include file in the /INCLUDE_DIRECTORY directories. It does not start by looking in the directory containing the including file or in the directory containing the top level source file.

**Table 1-14 /NESTED_INCLUDE_DIRECTORY Qualifier Options**
Option	Usage
PRIMARY_FILE	Directs the compiler to search the default file type for headers using the context of the primary source file (the .C file). This means that just the file type (".h" or ".") is used for the default file-spec, but the chain of "related file-specs" used to maintain the sticky defaults for processing the next top-level source file is also applied when searching for the include file. This most closely matches the behavior of VAX C.
INCLUDE_FILE	Directs the compiler to first search the directory of the source file containing the `#include` directive. If the file to be included is not found, the compiler continues searching by following normal inclusion rules.
NONE	Directs the compiler to skip the first step of processing `#include " file.h"` directives. The compiler starts its search for the include file in the /INCLUDE_DIRECTORY directories. It does not start by looking in the directory containing the including file or in the directory containing the top level source file.

The default is /NESTED_INCLUDE_DIRECTORY=INCLUDE_FILE.

/[NO]OBJECT[=file-spec]

Produces an object module. By default, /OBJECT creates an object module file with the same name as that of the first source file of a compilation unit and with the .OBJ file extension. If you include a file specification with /OBJECT, the compiler uses that specification instead.

The compiler executes faster if it does not have to produce an object module. Use the /NOOBJECT qualifier when you need only a listing of a program or when you want the compiler to check a source file for errors. The default is /OBJECT.

/[NO]OPTIMIZE[=(option[,...])]

Determines whether Compaq C performs code optimizations.

You can specify the options described in Table 1-15.

Table 1-15 /OPTIMIZE Qualifier Options
Option Usage

[NO]DISJOINT (VAX ONLY) Optimizes the generated machine code. For example, the compiler eliminates common subexpressions, removes invariant expressions from loops, collapses arithmetic operations into 3-operand instructions, and places local variables in registers.
When debugging Compaq C programs, use the
/OPTIMIZE=NODISJOINT option if you need minimal optimization; if optimization during debugging is not important, use the /NOOPTIMIZE qualifier.

[NO]INLINE (VAX ONLY) Provides automatic inline expansion of functions that yield optimized code when they are expanded. Whether or not a function is a candidate for inline expansion is based on its size, the number of times it is called, and whether it conforms to the rules specified in Section 5.4.8.

[NO]INLINE[= keyword] (ALPHA ONLY) Provides inline expansion of functions that yield optimized code when they are expanded. Whether or not a function is a candidate for inline expansion is based on its size, the number of times it is called, and whether it conforms to the rules specified in Section 5.4.8. On OpenVMS Alpha systems, you can specify one of the following keywords to control inlining:

NONE No inlining is done, even if requested by a #pragma inline preprocessor directive. /OPTIMIZE=INLINE=NONE is equivalent to /OPTIMIZE=NOINLINE.

MANUAL Inlines only those function calls explicitly requested for inlining by a #pragma inline directive.

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AUTOMATIC Inlines all of the function calls in the MANUAL category, plus any additional calls that the compiler determines would improve run-time performance. This is the default.

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ALL Inlines every call that can be inlined while still generating correct code. Recursive routines, however, will not cause an infinite loop at compile time.

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SIZE Provides behavior similar to that of the keyword AUTOMATIC in versions of DEC C before 5.0, although it is somewhat more conservative in most cases. For DEC C Version 5.0 and higher, AUTOMATIC is treated as a synonym for SIZE. SIZE inlines functions when the compiler determines that it can improve run-time performance without significantly increasing the size of the program.

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SPEED Performs more aggressive inlining for run-time performance, even when it might significantly increase the size of the program.

The #pragma noinline preprocessor directive can be used to prevent inlining of any particular functions under the compiler-selected forms of inlining (SPEED, SIZE, or AUTOMATIC).
The #pragma inline preprocessor directive (or the __inline storage-class modifier for OpenVMS Alpha systems) can be used to request inlining of specific functions under the AUTOMATIC or MANUAL forms of inlining.

[NO]INTRINSICS (ALPHA ONLY) Controls whether or not certain functions are handled as intrinsic functions without explicitly enabling each of them as an intrinsic through the #pragma intrinsic preprocessor directive. An intrinsic function is an apparent function call that could be handled as an actual call to the specified function, or could be handled by the compiler in a different manner. By treating the function as an intrinsic, the compiler can often generate faster code. (Contrast with a built-in function, which is an apparent function call that is never handled as an actual function call. There is never a function with the specified name.)
See Section 5.4.9 for a list of functions that can be handled as intrinsics.
The /OPTIMZE=INTRINSICS qualifier works together with /OPTIMIZE=LEVEL=n and some other qualifiers to determine how intrinsics are handled:

If the optimization level specified is less than 4, the intrinsic-function prototypes and call formats are checked, but normal run-time calls are still made.
If the optimization level is 4 or higher, intrinsic code is generated.
If /STANDARD=ANSI89 is specified, non-ANSI-Standard functions are not automatically intrinsic and do not even have their prototypes checked. They are only checked if the non-ANSI-Standard functions are made intrinsic through #pragma intrinsic.
Intrinsic code is not generated for math functions that set the errno variable unless /ASSUME=NOMATH_ERRNO is specified. Such math functions, however, do have their prototypes and call formats checked.

The default is /OPTIMIZE=INTRINSICS, which turns on this handling.
To turn it off, specify /NOOPTIMIZE or /OPTIMIZE=NOINTRINSICS, or specify an optimization level less than 4.

LEVEL= n (ALPHA ONLY) Selects the level of optimization. Specify an integer from 0 (no optimization) to 4 (full optimization):

0 Disables all optimizations. Does not check for unassigned variables.

1 Enables local optimizations and recognition of some common subexpressions. The call graph determines the order of compilation of procedures.

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2 Includes level 1 optimizations. Enables global optimization. This includes data-flow analysis, code motion, strength reduction and test replacement, split lifetime analysis, and code scheduling.

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3 Includes level 2 optimizations. Enables additional global optimizations that improve speed (at the cost of extra code size), for example: integer multiplication and division expansion (using shifts), loop unrolling, and code replication to eliminate branches.

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4 Includes level 3 optimizations. Enables interprocedural analysis and automatic inlining of small procedures (with heuristics limiting the amount of extra code). This is the default.

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5 Includes level 4 optimizations. Activates software pipelining, which is a specialized form of loop unrolling that in certain cases improves run-time performance. Software pipelining uses instruction scheduling to eliminate instruction stalls within loops, rearranging instructions between different unrolled loop iterations to improve performance.
Loops chosen for software pipelining are always innermost loops and do not contain branches or procedure calls. To determine whether using level 5 benefits your particular program, you should time program execution for the same program compiled at levels 4 and 5. For programs that contain loops that exhaust available registers, longer execution times may result with level 5.

[NO]PIPELINE (ALPHA ONLY) Controls Activation of the software pipelining optimization.
The software pipelining optimization applies instruction scheduling to certain innermost loops, allowing instructions within a loop to "wrap around" and execute in a different iteration of the loop. This can reduce the impact of long-latency operations, resulting in faster loop execution.
Software pipelining can be more effective when you combine /OPTIMIZE=PIPELINE with the appropriate /OPTIMIZE=TUNE keyword for the target Alpha processor generation.
Software pipelining also enables the prefetching of data to reduce the impact of cache misses.
Software pipelining is a subset of the optimizations activated by optimization level 5.
To determine whether using /OPTIMIZE=PIPELINE benefits your particular program, you should time program execution for the same program (or subprogram) compiled with and without software pipelining.
For programs containing loops that exhaust available registers, longer execution times can result with optimization level 5, requiring use of /OPTIMIZE=UNROLL= n to limit loop unrolling.

UNROLL= n (ALPHA ONLY) Controls loop unrolling done by the optimizer. UNROLL= n means to unroll loop bodies n times, where n is between 0 and 16. UNROLL=0 means the optimizer will use its own default unroll amount. Specify UNROLL only at level 3 or higher.

TUNE= keyword (ALPHA ONLY) Selects processor-specific instruction tuning for implementations of the Alpha architecture. Regardless of the setting of the /OPTIMIZE=TUNE flag, the generated code will run correctly on all implementations of the Alpha architecture. Tuning for a specific implementation can provide improvements in run-time performance. Code tuned for a specific target might run slower on another target.
You can specify one of the following keywords:

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GENERIC Selects instruction tuning that is appropriate for all implementations of the Alpha architecture. This option is the default.

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HOST Selects instruction tuning that is appropriate for the machine on which the code is being compiled.

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EV4 Selects instruction tuning for the 21064, 21064A, 21066, and 21068 implementations of the Alpha architecture.

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EV5 Selects instruction tuning for the 21164 implementation of the Alpha architecture.

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EV56 Selects instruction tuning for the 21164 chip implementations that use the byte- and word-manipulation instruction extensions of the Alpha architecture.
Running programs compiled with the EV56 keyword might incur emulation overhead on EV4 and EV5 processors, but will still run correctly on OpenVMS Version 7.1 (or higher).

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PCA56 Selects instruction tuning for the 21164PC implementation that uses the byte- and word-manipulation instruction extensions and multimedia instruction extensions of the Alpha architecture.
Running programs compiled with the PCA56 keyword might incur emulation overhead on EV4, EV5, and EV56 processors, but will still run correctly on OpenVMS Version 7.1 (or higher).

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EV6 Selects instruction tuning for the first-generation 21264 implementation of the Alpha architecture.

EV67 Selects instruction tuning for the second-generation 21264 implementation of the Alpha architecture.

For OpenVMS VAX systems the default, /OPTIMIZE, is equivalent to /OPTIMIZE=(DISJOINT,INLINE).