mirror of
https://github.com/carbon-language/carbon-lang.git
synced 2026-11-15 09:28:30 +00:00
Chandler Carruth
0546b48a7d
Add support to the driver for CLI flags that select which CPU to target, which CPU to tune performance for, and which CPU features to enable. - `--target-cpu` selects the architecture of CPU to target, similar to `-march` on x86. This combines `-march` with `armv*` strings and `-mcpu` on Arm for specific CPU names. Similarly for RISC-V (if/when we support and test it), etc. Notably, `--target-cpu=native` targets the current native CPU. - `--target-cpu-tune` maps to `-mtune`. This is expected to be rarely if ever desirable, and I'm open to removing it, but if folks are relying on this for performance I didn't want to hide the option. - `--target-cpu-features` allows a "standard" (for LLVM) comma-separated list of LLVM subtarget features, including `+feature` and `-feature` syntax. These flags, when provided, establish the default baseline for CPU targeting and control how on-demand runtimes are built. They can be changed or overridden by additional Clang flags when using `--clang-arg`. A critical part of this is building runtimes on demand using these features. For that, we need to do some amount of canonicalization (re-using Clang's canonicalization to ensure consistent behavior), and extend the runtimes cache features to recognize these customizations. Note that only the top-level Carbon flags impact runtimes, any particular Clang arguments are only used by the specific compiles that receive those arguments. There is some nascent RISC-V support here, but it is incomplete and only minimally tested. Still, it seemed better to record the parts we could test than remove them. Assisted-by: Antigravity with Gemini