Optimization and tuning

Attempts to inline functions instead of generating calls to those functions, for improved performance.

Indicates whether a program contains certain categories of aliasing or does not conform to C/C++ standard aliasing rules. The compiler limits the scope of some optimizations when there is a possibility that different names are aliases for the same storage location.

Controls loop unrolling, for improved performance.

Equivalent pragma: #pragma unroll

Specifies the visibility attribute for external linkage entities in object files. The external linkage entities have the visibility attribute that is specified by the -fvisibility option if they do not get visibility attributes from pragma directives, explicitly specified attributes, or propagation rules.

Equivalent pragma: #pragma GCC visibility push, #pragma GCC visibility pop

Specifies the processor architecture for which the code (instructions) should be generated.

Tunes instruction selection, scheduling, and other architecture-dependent performance enhancements to run best on a specific hardware architecture. Allows specification of a target SMT mode to direct optimizations for best performance in that mode.

Specifies whether to optimize code during compilation and, if so, at which level.

Prepares the object files produced by the compiler for profiling.

Enables destructive copy operations for structures and unions.

Specifies the cache configuration for a specific execution machine.

Avoids optimizations that increase code size.

Marks data as local or imported.

Informs the compiler that a given compilation unit may reference write-through-enabled or cache-inhibited storage.

Performs high-order loop analysis and transformations (HOT) during optimization.

Equivalent pragma: #pragma nosimd

Allows the compiler to perform optimizations as if system calls would not modify errno.

Enables or customizes a class of optimizations known as interprocedural analysis (IPA).

Specifies functions in the source file that have no side effects other than those implied by their parameters.

Assumes that all functions with the name of an ANSI C library function are in fact the system functions.

Limits the amount of memory that the compiler allocates while performing specific, memory-intensive optimizations to the specified number of kilobytes.

Tunes optimizations through profile-directed feedback (PDF), where results from sample program execution are used to improve optimization near conditional branches and in frequently executed code sections.

Inserts prefetch instructions automatically where there are opportunities to improve code performance.

When used with -qpdf1 and a minimum optimization level of -O2 at compile and link steps, creates a PDF map file that contains additional profiling information for all procedures in your application.

Controls whether the compiler can automatically take advantage of vector instructions for processors that support them.

Equivalent pragma: #pragma nosimd

Reduces the size of the stack frame.

Ensures that optimizations done by default at the -O3 and higher optimization levels, and, optionally at -O2, do not alter the semantics of a program.

Prevents the compiler from performing induction (loop counter) variable optimizations. These optimizations may be unsafe (may alter the semantics of your program) when there are integer overflow operations involving the induction variables.

Specifies whether the call stack can be unwound by code looking through the saved registers on the stack.