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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 bb8b11e67d
12 changed files with 226 additions and 14 deletions
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12
compiler/rustc_hir_analysis/src/check/intrinsic.rs
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@ -123,7 +123,12 @@ pub fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: LocalDefId) -
| sym::variant_count
| sym::is_val_statically_known
| sym::ptr_mask
| sym::debug_assertions => hir::Unsafety::Normal,
| sym::debug_assertions
| sym::fadd_algebraic
| sym::fsub_algebraic
| sym::fmul_algebraic
| sym::fdiv_algebraic
| sym::frem_algebraic => hir::Unsafety::Normal,
_ => hir::Unsafety::Unsafe,
};
@ -405,6 +410,11 @@ pub fn check_intrinsic_type(
sym::fadd_fast | sym::fsub_fast | sym::fmul_fast | sym::fdiv_fast | sym::frem_fast => {
(1, 0, vec![param(0), param(0)], param(0))
}
sym::fadd_algebraic
| sym::fsub_algebraic
| sym::fmul_algebraic
| sym::fdiv_algebraic
| sym::frem_algebraic => (1, 0, vec![param(0), param(0)], param(0)),
sym::float_to_int_unchecked => (2, 0, vec![param(0)], param(1)),
sym::assume => (0, 1, vec![tcx.types.bool], Ty::new_unit(tcx)),