bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

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

Browse source 
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
Download patch file Download diff file Expand all files Collapse all files

32
compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
View file

@ -250,6 +250,38 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
}
}
}
sym::fadd_algebraic
| sym::fsub_algebraic
| sym::fmul_algebraic
| sym::fdiv_algebraic
| sym::frem_algebraic => match float_type_width(arg_tys[0]) {
Some(_width) => match name {
sym::fadd_algebraic => {
bx.fadd_algebraic(args[0].immediate(), args[1].immediate())
}
sym::fsub_algebraic => {
bx.fsub_algebraic(args[0].immediate(), args[1].immediate())
}
sym::fmul_algebraic => {
bx.fmul_algebraic(args[0].immediate(), args[1].immediate())
}
sym::fdiv_algebraic => {
bx.fdiv_algebraic(args[0].immediate(), args[1].immediate())
}
sym::frem_algebraic => {
bx.frem_algebraic(args[0].immediate(), args[1].immediate())
}
_ => bug!(),
},
None => {
bx.tcx().dcx().emit_err(InvalidMonomorphization::BasicFloatType {
span,
name,
ty: arg_tys[0],
});
return Ok(());
}
},
sym::float_to_int_unchecked => {
if float_type_width(arg_tys[0]).is_none() {

5
compiler/rustc_codegen_ssa/src/traits/builder.rs
View file

@ -86,22 +86,27 @@ pub trait BuilderMethods<'a, 'tcx>:
fn add(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fadd(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fadd_fast(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fadd_algebraic(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn sub(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fsub(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fsub_fast(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fsub_algebraic(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn mul(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fmul(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fmul_fast(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fmul_algebraic(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn udiv(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn exactudiv(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn sdiv(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn exactsdiv(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fdiv(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fdiv_fast(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn fdiv_algebraic(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn urem(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn srem(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn frem(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn frem_fast(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn frem_algebraic(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn shl(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn lshr(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;
fn ashr(&mut self, lhs: Self::Value, rhs: Self::Value) -> Self::Value;