From a93a9aa2d57564660b2c28e5c1cdda7943989f17 Mon Sep 17 00:00:00 2001 From: Scott McMurray Date: Sun, 20 Jul 2025 00:17:22 -0700 Subject: Don't emit two `assume`s in transmutes when one is a subset of the other For example, transmuting between `bool` and `Ordering` doesn't need two `assume`s because one range is a superset of the other. Multiple are still used for things like `char` <-> `NonZero`, which overlap but where neither fully contains the other. --- compiler/rustc_codegen_ssa/src/mir/rvalue.rs | 28 ++++++++++++++++++++++++---- 1 file changed, 24 insertions(+), 4 deletions(-) (limited to 'compiler/rustc_codegen_ssa/src') diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs index 610e2fd2311..a5759b79be4 100644 --- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs +++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs @@ -288,7 +288,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> { // valid ranges. For example, `char`s are passed as just `i32`, with no // way for LLVM to know that they're 0x10FFFF at most. Thus we assume // the range of the input value too, not just the output range. - assume_scalar_range(bx, imm, from_scalar, from_backend_ty); + assume_scalar_range(bx, imm, from_scalar, from_backend_ty, None); imm = match (from_scalar.primitive(), to_scalar.primitive()) { (Int(_, is_signed), Int(..)) => bx.intcast(imm, to_backend_ty, is_signed), @@ -1064,7 +1064,7 @@ pub(super) fn transmute_scalar<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( // That said, last time we tried removing this, it didn't actually help // the rustc-perf results, so might as well keep doing it // - assume_scalar_range(bx, imm, from_scalar, from_backend_ty); + assume_scalar_range(bx, imm, from_scalar, from_backend_ty, Some(&to_scalar)); imm = match (from_scalar.primitive(), to_scalar.primitive()) { (Int(..) | Float(_), Int(..) | Float(_)) => bx.bitcast(imm, to_backend_ty), @@ -1092,22 +1092,42 @@ pub(super) fn transmute_scalar<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( // since it's never passed to something with parameter metadata (especially // after MIR inlining) so the only way to tell the backend about the // constraint that the `transmute` introduced is to `assume` it. - assume_scalar_range(bx, imm, to_scalar, to_backend_ty); + assume_scalar_range(bx, imm, to_scalar, to_backend_ty, Some(&from_scalar)); imm = bx.to_immediate_scalar(imm, to_scalar); imm } +/// Emits an `assume` call that `imm`'s value is within the known range of `scalar`. +/// +/// If `known` is `Some`, only emits the assume if it's more specific than +/// whatever is already known from the range of *that* scalar. fn assume_scalar_range<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( bx: &mut Bx, imm: Bx::Value, scalar: abi::Scalar, backend_ty: Bx::Type, + known: Option<&abi::Scalar>, ) { - if matches!(bx.cx().sess().opts.optimize, OptLevel::No) || scalar.is_always_valid(bx.cx()) { + if matches!(bx.cx().sess().opts.optimize, OptLevel::No) { return; } + match (scalar, known) { + (abi::Scalar::Union { .. }, _) => return, + (_, None) => { + if scalar.is_always_valid(bx.cx()) { + return; + } + } + (abi::Scalar::Initialized { valid_range, .. }, Some(known)) => { + let known_range = known.valid_range(bx.cx()); + if valid_range.contains_range(known_range, scalar.size(bx.cx())) { + return; + } + } + } + match scalar.primitive() { abi::Primitive::Int(..) => { let range = scalar.valid_range(bx.cx()); -- cgit 1.4.1-3-g733a5