bjoernager/rust
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Change signature of target_features_cfg.

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Currently it is called twice, once with `allow_unstable` set to true and
once with it set to false. This results in some duplicated work. Most
notably, for the LLVM backend, `LLVMRustHasFeature` is called twice for
every feature, and it's moderately slow. For very short running
compilations on platforms with many features (e.g. a `check` build of
hello-world on x86) this is a significant fraction of runtime.

This commit changes `target_features_cfg` so it is only called once, and
it now returns a pair of feature sets. This halves the number of
`LLVMRustHasFeature` calls.
This commit is contained in:
Nicholas Nethercote 2025-02-25 15:25:54 +11:00
parent 2df8e657f2
commit 936a8232df
6 changed files with 85 additions and 71 deletions
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8
compiler/rustc_interface/src/util.rs
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@ -39,11 +39,11 @@ pub(crate) fn add_configuration(
) {
let tf = sym::target_feature;
let unstable_target_features = codegen_backend.target_features_cfg(sess, true);
sess.unstable_target_features.extend(unstable_target_features.iter().cloned());
let (target_features, unstable_target_features) = codegen_backend.target_features_cfg(sess);
let target_features = codegen_backend.target_features_cfg(sess, false);
sess.target_features.extend(target_features.iter().cloned());
sess.unstable_target_features.extend(unstable_target_features.iter().copied());
sess.target_features.extend(target_features.iter().copied());
cfg.extend(target_features.into_iter().map(|feat| (tf, Some(feat))));