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Auto merge of #133984 - DaniPopes:scmp-ucmp, r=scottmcm

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Lower BinOp::Cmp to llvm.{s,u}cmp.* intrinsics

Lowers `mir::BinOp::Cmp` (`three_way_compare` intrinsic) to the corresponding LLVM `llvm.{s,u}cmp.i8.*` intrinsics.

These are the intrinsics mentioned in https://github.com/rust-lang/rust/pull/118310, which are now available in LLVM 19.

I couldn't find any follow-up PRs/discussions about this, please let me know if I missed something.

r? `@scottmcm`
This commit is contained in:
bors 2025-03-24 22:53:12 +00:00
commit 1df5affaca
8 changed files with 124 additions and 42 deletions
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30
compiler/rustc_codegen_llvm/src/builder.rs
View file

@ -14,6 +14,7 @@ use rustc_codegen_ssa::mir::place::PlaceRef;
use rustc_codegen_ssa::traits::*;
use rustc_data_structures::small_c_str::SmallCStr;
use rustc_hir::def_id::DefId;
use rustc_middle::bug;
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
use rustc_middle::ty::layout::{
FnAbiError, FnAbiOfHelpers, FnAbiRequest, HasTypingEnv, LayoutError, LayoutOfHelpers,
@ -1074,6 +1075,35 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
unsafe { llvm::LLVMBuildFCmp(self.llbuilder, op as c_uint, lhs, rhs, UNNAMED) }
}
fn three_way_compare(
&mut self,
ty: Ty<'tcx>,
lhs: Self::Value,
rhs: Self::Value,
) -> Option<Self::Value> {
// FIXME: See comment on the definition of `three_way_compare`.
if crate::llvm_util::get_version() < (20, 0, 0) {
return None;
}
let name = match (ty.is_signed(), ty.primitive_size(self.tcx).bits()) {
(true, 8) => "llvm.scmp.i8.i8",
(true, 16) => "llvm.scmp.i8.i16",
(true, 32) => "llvm.scmp.i8.i32",
(true, 64) => "llvm.scmp.i8.i64",
(true, 128) => "llvm.scmp.i8.i128",
(false, 8) => "llvm.ucmp.i8.i8",
(false, 16) => "llvm.ucmp.i8.i16",
(false, 32) => "llvm.ucmp.i8.i32",
(false, 64) => "llvm.ucmp.i8.i64",
(false, 128) => "llvm.ucmp.i8.i128",
_ => bug!("three-way compare unsupported for type {ty:?}"),
};
Some(self.call_intrinsic(name, &[lhs, rhs]))
}
/* Miscellaneous instructions */
fn memcpy(
&mut self,

12
compiler/rustc_codegen_llvm/src/context.rs
View file

@ -1127,6 +1127,18 @@ impl<'ll> CodegenCx<'ll, '_> {
ifn!("llvm.usub.sat.i64", fn(t_i64, t_i64) -> t_i64);
ifn!("llvm.usub.sat.i128", fn(t_i128, t_i128) -> t_i128);
ifn!("llvm.scmp.i8.i8", fn(t_i8, t_i8) -> t_i8);
ifn!("llvm.scmp.i8.i16", fn(t_i16, t_i16) -> t_i8);
ifn!("llvm.scmp.i8.i32", fn(t_i32, t_i32) -> t_i8);
ifn!("llvm.scmp.i8.i64", fn(t_i64, t_i64) -> t_i8);
ifn!("llvm.scmp.i8.i128", fn(t_i128, t_i128) -> t_i8);
ifn!("llvm.ucmp.i8.i8", fn(t_i8, t_i8) -> t_i8);
ifn!("llvm.ucmp.i8.i16", fn(t_i16, t_i16) -> t_i8);
ifn!("llvm.ucmp.i8.i32", fn(t_i32, t_i32) -> t_i8);
ifn!("llvm.ucmp.i8.i64", fn(t_i64, t_i64) -> t_i8);
ifn!("llvm.ucmp.i8.i128", fn(t_i128, t_i128) -> t_i8);
ifn!("llvm.lifetime.start.p0i8", fn(t_i64, ptr) -> void);
ifn!("llvm.lifetime.end.p0i8", fn(t_i64, ptr) -> void);