mtune

mtune is a compiler option used by GCC and compatible toolchains to optimize generated code for a specific CPU or microarchitecture without enabling new instructions. It influences code generation decisions such as instruction scheduling and register allocation, applying microarchitectural considerations within the constraints of the selected instruction set architecture.

Usage and interaction: mtune is typically used in combination with -march, which selects the ISA, while -mtune tunes performance for a particular CPU within that ISA. A common form is -mtune=name, where name designates a target CPU or host. Examples include -march=haswell -mtune=haswell, or -mtune=native to optimize for the host processor. On ARM, examples may include -mtune=cortex-a57 or other core names supported by the toolchain.

Notes and limitations: -mtune does not enable new instructions; it adjusts optimization strategies to suit the chosen target. The set of valid values is architecture-dependent, and on some targets the option may have little or no effect. The benefits of -mtune can vary between toolchains and platforms, and it should be used with an appropriate -march to avoid misleading results.

Overview: In practice, developers use -mtune to extract additional performance from existing hardware while preserving compatibility with the selected ISA. It is one of several tuning options in GCC, alongside -march and -mcpu, and its specific behavior depends on the architecture and toolchain.

See also: -march, -mcpu, -mtune in the GCC manual, GCC, Clang.