Profile-Guided Optimization (PGO) Quick Reference

-prof-gen

/Qprof-gen

Instruments a program for profiling to get the execution count of each basic block. The option is used in phase 1 (instrumenting the code) to instruct the compiler to produce instrumented code in your object files in preparation for instrumented execution. Results in dynamic-information (.dyn) file.

With the x qualifier, the option gathers extra source information, which enables using specific tools, like the code-coverage tool. The extended option does not provide better optimization and using it could slow compile time.

If you are performing a parallel make, this option will not affect it.

For more information, see the following topic:

• -prof-gen compiler option

-prof-use

/Qprof-use

Instructs the compiler to produce a profile-optimized executable and merges available dynamic-information (.dyn) files into a pgopti.dpi file. This option is used in used in phase 3 (generating a profile-optimized executable).

The dynamic-information files are produced in phase 2 when you run the instrumented executable.

If you perform multiple executions of the instrumented program, this option merges the dynamic-information files again and overwrites the previous pgopti.dpi file.

Linux:

• Using this option with -func-groups allows you to control function grouping behavior.

For more information, see the following topic:

• -prof-use compiler option

-fnsplit-

/Qfnsplit-

Disables function splitting. Function splitting is enabled by the prof-use option in phase 3 to improve code locality by splitting routines into different sections: one section to contain the cold or very infrequently executed (cold) code, and one section to contain the rest of the frequently executed (hot) code. You may want to disable function splitting for the following reasons:

• Improve debugging capability. In the debug symbol table, it is difficult to represent a split routine, that is, a routine with some of its code in the hot code section and some of its code in the cold code section.

• Account for the cases when the profile data does not represent the actual program behavior, that is, when the routine is actually used frequently rather than infrequently.

Mac OS: This option is not supported.

Windows: This option behaves differently on systems based on IA-32 architecture that it does on systems based on IA-64 architecture.

IA-32 architecture:

• The option completely disables function splitting, placing all the code in one section.

IA-64 architecture:

• The option disables the splitting within a routine but enables function grouping, an optimization in which entire routines are placed either in the cold code section or the hot code section.  Function grouping does not degrade debugging capability.

For more information, see the following topic:

• -fnsplit compiler option

-prof-dir

/Qprof-dir

Specifies the directory in which dynamic information (.dyn) files are created and stored; otherwise, the .dyn files are placed in the directory where the program is compiled.

For more information, see the following topic:

• -prof-dir compiler option

-prof-file

/Qprof-file

Specifies file name for profiling summary file. If this option is not specified the summary information is stored in the default file: pgopti.dpi.

For more information, see the following topic:

• -prof-file compiler option

-prof-gen-sampling

/Qprof-gen-sampling

IA-32 architecture. Prepares application executables for hardware profiling (sampling) and causes the compiler to generate source code mapping information.

Mac OS: This option is not supported.

For more information, see the following topic:

• -prof-gen-sampling compiler option

-ssp

/Qssp

IA-32 architecture. Enables Software-based Speculative Pre-computation (SSP) optimization.

Mac OS: This option is not supported.

For more information, see the following topic:

• -ssp compiler option

-finstrument-functions

/Qinstrument-functions

Enables the ability to gather information about developer-created profiling functions. Enables inlining for a specific function even if inlining has been disabled for the compilation.

For more information, see the following topic:

• -finstrument-functions compiler option