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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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15
compiler/rustc_codegen_cranelift/src/lib.rs
View File

@@ -41,8 +41,8 @@ use std::sync::Arc;
use cranelift_codegen::isa::TargetIsa;
use cranelift_codegen::settings::{self, Configurable};
use rustc_codegen_ssa::CodegenResults;
use rustc_codegen_ssa::traits::CodegenBackend;
use rustc_codegen_ssa::{CodegenResults, TargetConfig};
use rustc_metadata::EncodedMetadata;
use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
use rustc_session::Session;
@@ -178,7 +178,7 @@ impl CodegenBackend for CraneliftCodegenBackend {
}
}
fn target_features_cfg(&self, sess: &Session) -> (Vec<Symbol>, Vec<Symbol>) {
fn target_config(&self, sess: &Session) -> TargetConfig {
// FIXME return the actually used target features. this is necessary for #[cfg(target_feature)]
let target_features = if sess.target.arch == "x86_64" && sess.target.os != "none" {
// x86_64 mandates SSE2 support and rustc requires the x87 feature to be enabled
@@ -197,7 +197,16 @@ impl CodegenBackend for CraneliftCodegenBackend {
};
// FIXME do `unstable_target_features` properly
let unstable_target_features = target_features.clone();
(target_features, unstable_target_features)
TargetConfig {
target_features,
unstable_target_features,
// Cranelift does not yet support f16 or f128
has_reliable_f16: false,
has_reliable_f16_math: false,
has_reliable_f128: false,
has_reliable_f128_math: false,
}
}
fn print_version(&self) {