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Rollup merge of #136543 - RalfJung:round-ties-even, r=tgross35

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intrinsics: unify rint, roundeven, nearbyint in a single round_ties_even intrinsic

LLVM has three intrinsics here that all do the same thing (when used in the default FP environment). There's no reason Rust needs to copy that historically-grown mess -- let's just have one intrinsic and leave it up to the LLVM backend to decide how to lower that.

Suggested by `@hanna-kruppe` in https://github.com/rust-lang/rust/issues/136459; Cc `@tgross35`

try-job: test-various
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Trevor Gross 2025-02-23 14:30:25 -05:00 • committed by GitHub
commit a2bb4d748d
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13 changed files with 127 additions and 208 deletions
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22
compiler/rustc_codegen_llvm/src/intrinsic.rs
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@ -127,15 +127,14 @@ fn get_simple_intrinsic<'ll>(
sym::truncf64 => "llvm.trunc.f64",
sym::truncf128 => "llvm.trunc.f128",
sym::rintf16 => "llvm.rint.f16",
sym::rintf32 => "llvm.rint.f32",
sym::rintf64 => "llvm.rint.f64",
sym::rintf128 => "llvm.rint.f128",
sym::nearbyintf16 => "llvm.nearbyint.f16",
sym::nearbyintf32 => "llvm.nearbyint.f32",
sym::nearbyintf64 => "llvm.nearbyint.f64",
sym::nearbyintf128 => "llvm.nearbyint.f128",
// We could use any of `rint`, `nearbyint`, or `roundeven`
// for this -- they are all identical in semantics when
// assuming the default FP environment.
// `rint` is what we used for $forever.
sym::round_ties_even_f16 => "llvm.rint.f16",
sym::round_ties_even_f32 => "llvm.rint.f32",
sym::round_ties_even_f64 => "llvm.rint.f64",
sym::round_ties_even_f128 => "llvm.rint.f128",
sym::roundf16 => "llvm.round.f16",
sym::roundf32 => "llvm.round.f32",
@ -144,11 +143,6 @@ fn get_simple_intrinsic<'ll>(
sym::ptr_mask => "llvm.ptrmask",
sym::roundevenf16 => "llvm.roundeven.f16",
sym::roundevenf32 => "llvm.roundeven.f32",
sym::roundevenf64 => "llvm.roundeven.f64",
sym::roundevenf128 => "llvm.roundeven.f128",
_ => return None,
};
Some(cx.get_intrinsic(llvm_name))