5.7.7 Options for Controlling Optimization

The options tabulated below control compiler optimizations and are described in the sections that follow.

Table 5-15. Optimization Options
Option	Controls
`-O0`	Do not optimize.
`-O` `-O1`	Optimization level 1.
`-O2`	Optimization level 2.
`-O3`	Speed-orientated optimizations.
`-Os`	Size-orientated optimizations.
`-f[no-]align-functions=n`	Alignment of the start of functions.
`-f[no-]align-jumps=n`	Alignment of jump targets
`-f[no-]align-labels=n`	Alignment of all branch targets.
`-f[no-]align-loops=n`	Alignment of loops.
`-f[no-]caller-saves`	Allocation into registers clobbered by function calls.
`-f[no-]cse-follow-jumps`	Customization of common subexpression elimination optimizations.
`-f[no-]cse-skip-blocks`	Customization of common subexpression elimination optimizations.
`-f[no-]data-sections`	Placement of objects into a section in the output file.
`-f[no-]defer-pop`	When arguments to function calls are popped.
`-f[no-]expensive-optimizations`	Minor optimizations that are relatively expensive.
`-ffat-lto-objects`	Requests that the compiler generate fat object files.
`-f[no-]function-cse`	Placement of function addresses.
`-f[no-]function-sections`	Placement of functions into a section in the output file.
`-f[no-]gcse`	The global common subexpression elimination pass.
`-f[no-]gcse-lm`	Customization of common subexpression elimination dealing with loads.
`-f[no-]gcse-sm`	Customization of common subexpression elimination dealing with stores.
`-finline`	Inlining of functions marked with the inline specifier
`-f[no-]inline-functions`	Integration of all simple functions into their callers.
`-f[no-]inline-limit=n`	The size limit for inlining functions.
`-finline-small-functions`	Integration of all simple functions into their callers.
`-f[no-]keep-inline-functions`	Output of a separate run-time-callable version of inlined functions.
`-f[no-]keep-static-consts`	Output of `static const` objects.
`-f[no-]lto`	The standard link-time optimizer.
`-flto-partition=algorithm`	The link-time optimizer algorithm used to partition object files.
`-f[no-]omit-frame-pointer`	Reservation of the Frame Pointer in a register for functions that don't need one.
`-f[no-]optimize-register-move` `-f[no-]regmove`	Reassign of register numbers in move and other instructions.
`-f[no-]optimize-sibling-calls`	Optimization of sibling and tail recursive calls.
`-fpeel-loops`	Reconfigure loops in the source code.
`-f[no-]peephole` `-f[no-]peephole2`	Machine-specific peephole optimizations.
`-f[no-]rename-registers`	Use of free registers to avoid false dependencies in scheduled code.
`-f[no-]rerun-cse-after-loop`	When common subexpression elimination optimizations should be performed.
`-f[no-]rerun-loop-opt`	How often to run the loop optimizer.
`-f[no-]schedule-insns` `-f[no-]schedule-insns2`	Reordering instructions to eliminate instruction stalls.
`-f[no-]strength-reduce`	Loop strength reduction and elimination of iteration variables.
`-f[no-]strict-aliasing`	Assumption of the strictest aliasing rules applicable to the language being compiled.
`-f[no-]thread-jumps`	Jump-to-branch optimizations.
`-f[no-]toplevel-reorder`	Reordering of top-level functions, variables, and `asm` statements.
`-ftracer`	Perform tail duplication.
`-ftree-vrp`	Perform value range propagation.
`-ftrivial-auto-var-init=choice`	Initialize automatic variables that have not been explicitly initialized in the source code
`-f[no-]unroll-loops` `-f[no-]unroll-all-loops`	Loop unrolling.
`-fuse-linker-plugin`	Enable use of a linker plugin during link-time optimization plugin.
`-f[no-]whole-program`	More aggressive interprocedural optimizations.
`-fzero-call-used-regs=choice`	Overwriting "call-used" registers associated with functions when they return