From 5d16a7b88450624971004ffc2ce6dbde0bb03871 Mon Sep 17 00:00:00 2001 From: Scott McMurray Date: Thu, 19 Jun 2025 21:44:01 -0700 Subject: Avoid a bitcast FFI call in transmuting For things that only change the valid ranges, we can just skip the `LLVMBuildBitCast` call. I tried to tweak this a bit more and broke stuff, so I also added some extra tests for that as we apparently didn't have coverage. --- compiler/rustc_codegen_ssa/src/mir/rvalue.rs | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) (limited to 'compiler/rustc_codegen_ssa') diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs index e1d8b7546cf..db5ac6a514f 100644 --- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs +++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs @@ -1123,7 +1123,7 @@ pub(super) fn transmute_immediate<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( // While optimizations will remove no-op transmutes, they might still be // there in debug or things that aren't no-op in MIR because they change // the Rust type but not the underlying layout/niche. - if from_scalar == to_scalar && from_backend_ty == to_backend_ty { + if from_scalar == to_scalar { return imm; } @@ -1142,7 +1142,13 @@ pub(super) fn transmute_immediate<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( assume_scalar_range(bx, imm, from_scalar, from_backend_ty); imm = match (from_scalar.primitive(), to_scalar.primitive()) { - (Int(..) | Float(_), Int(..) | Float(_)) => bx.bitcast(imm, to_backend_ty), + (Int(..) | Float(_), Int(..) | Float(_)) => { + if from_backend_ty == to_backend_ty { + imm + } else { + bx.bitcast(imm, to_backend_ty) + } + } (Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty), (Int(..), Pointer(..)) => bx.ptradd(bx.const_null(bx.type_ptr()), imm), (Pointer(..), Int(..)) => { -- cgit 1.4.1-3-g733a5