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Implement the internal feature cfg_target_has_reliable_f16_f128

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Support for `f16` and `f128` is varied across targets, backends, and
backend versions. Eventually we would like to reach a point where all
backends support these approximately equally, but until then we have to
work around some of these nuances of support being observable.

Introduce the `cfg_target_has_reliable_f16_f128` internal feature, which
provides the following new configuration gates:

* `cfg(target_has_reliable_f16)`
* `cfg(target_has_reliable_f16_math)`
* `cfg(target_has_reliable_f128)`
* `cfg(target_has_reliable_f128_math)`

`reliable_f16` and `reliable_f128` indicate that basic arithmetic for
the type works correctly. The `_math` versions indicate that anything
relying on `libm` works correctly, since sometimes this hits a separate
class of codegen bugs.

These options match configuration set by the build script at [1]. The
logic for LLVM support is duplicated as-is from the same script. There
are a few possible updates that will come as a follow up.

The config introduced here is not planned to ever become stable, it is
only intended to replace the build scripts for `std` tests and
`compiler-builtins` that don't have any way to configure based on the
codegen backend.

MCP: https://github.com/rust-lang/compiler-team/issues/866
Closes: https://github.com/rust-lang/compiler-team/issues/866

[1]: 555e1d0386/library/std/build.rs (L84-L186)
This commit is contained in:
Trevor Gross
2025-04-24 22:11:23 +00:00
parent 555e1d0386
commit 6ceeb0849e
20 changed files with 311 additions and 27 deletions
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21
compiler/rustc_interface/src/util.rs
View File

@@ -38,14 +38,25 @@ pub(crate) fn add_configuration(
codegen_backend: &dyn CodegenBackend,
) {
let tf = sym::target_feature;
let tf_cfg = codegen_backend.target_config(sess);
let (target_features, unstable_target_features) = codegen_backend.target_features_cfg(sess);
sess.unstable_target_features.extend(tf_cfg.unstable_target_features.iter().copied());
sess.target_features.extend(tf_cfg.target_features.iter().copied());
sess.unstable_target_features.extend(unstable_target_features.iter().copied());
cfg.extend(tf_cfg.target_features.into_iter().map(|feat| (tf, Some(feat))));
sess.target_features.extend(target_features.iter().copied());
cfg.extend(target_features.into_iter().map(|feat| (tf, Some(feat))));
if tf_cfg.has_reliable_f16 {
cfg.insert((sym::target_has_reliable_f16, None));
}
if tf_cfg.has_reliable_f16_math {
cfg.insert((sym::target_has_reliable_f16_math, None));
}
if tf_cfg.has_reliable_f128 {
cfg.insert((sym::target_has_reliable_f128, None));
}
if tf_cfg.has_reliable_f128_math {
cfg.insert((sym::target_has_reliable_f128_math, None));
}
if sess.crt_static(None) {
cfg.insert((tf, Some(sym::crt_dash_static)));