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Auto merge of #120718 - saethlin:reasonable-fast-math, r=nnethercote

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Add "algebraic" fast-math intrinsics, based on fast-math ops that cannot return poison

Setting all of LLVM's fast-math flags makes our fast-math intrinsics very dangerous, because some inputs are UB. This set of flags permits common algebraic transformations, but according to the [LangRef](https://llvm.org/docs/LangRef.html#fastmath), only the flags `nnan` (no nans) and `ninf` (no infs) can produce poison.

And this uses the algebraic float ops to fix https://github.com/rust-lang/rust/issues/120720

cc `@orlp`
This commit is contained in:
bors 2024-02-21 09:43:33 +00:00
commit 709c00a047
1 changed files with 15 additions and 6 deletions
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21
src/intrinsics/mod.rs
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@ -1152,17 +1152,26 @@ fn codegen_regular_intrinsic_call<'tcx>(
ret.write_cvalue(fx, ret_val);
}
sym::fadd_fast | sym::fsub_fast | sym::fmul_fast | sym::fdiv_fast | sym::frem_fast => {
sym::fadd_fast
| sym::fsub_fast
| sym::fmul_fast
| sym::fdiv_fast
| sym::frem_fast
| sym::fadd_algebraic
| sym::fsub_algebraic
| sym::fmul_algebraic
| sym::fdiv_algebraic
| sym::frem_algebraic => {
intrinsic_args!(fx, args => (x, y); intrinsic);
let res = crate::num::codegen_float_binop(
fx,
match intrinsic {
sym::fadd_fast => BinOp::Add,
sym::fsub_fast => BinOp::Sub,
sym::fmul_fast => BinOp::Mul,
sym::fdiv_fast => BinOp::Div,
sym::frem_fast => BinOp::Rem,
sym::fadd_fast | sym::fadd_algebraic => BinOp::Add,
sym::fsub_fast | sym::fsub_algebraic => BinOp::Sub,
sym::fmul_fast | sym::fmul_algebraic => BinOp::Mul,
sym::fdiv_fast | sym::fdiv_algebraic => BinOp::Div,
sym::frem_fast | sym::frem_algebraic => BinOp::Rem,
_ => unreachable!(),
},
x,