From e1b020df9f72eab7e8b3e38a5263ddda54ce18e1 Mon Sep 17 00:00:00 2001 From: Scott McMurray Date: Fri, 26 May 2023 03:32:22 -0700 Subject: Use `load`-`store` instead of `memcpy` for short integer arrays --- compiler/rustc_codegen_ssa/src/base.rs | 14 +++++++++++++- compiler/rustc_codegen_ssa/src/traits/type_.rs | 22 ++++++++++++++++++++++ 2 files changed, 35 insertions(+), 1 deletion(-) (limited to 'compiler/rustc_codegen_ssa') diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs index 242d209b684..dc4a28c866f 100644 --- a/compiler/rustc_codegen_ssa/src/base.rs +++ b/compiler/rustc_codegen_ssa/src/base.rs @@ -380,7 +380,19 @@ pub fn memcpy_ty<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( return; } - bx.memcpy(dst, dst_align, src, src_align, bx.cx().const_usize(size), flags); + if flags == MemFlags::empty() + && let Some(bty) = bx.cx().scalar_copy_backend_type(layout) + { + // I look forward to only supporting opaque pointers + let pty = bx.type_ptr_to(bty); + let src = bx.pointercast(src, pty); + let dst = bx.pointercast(dst, pty); + + let temp = bx.load(bty, src, src_align); + bx.store(temp, dst, dst_align); + } else { + bx.memcpy(dst, dst_align, src, src_align, bx.cx().const_usize(size), flags); + } } pub fn codegen_instance<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>>( diff --git a/compiler/rustc_codegen_ssa/src/traits/type_.rs b/compiler/rustc_codegen_ssa/src/traits/type_.rs index 36d9864221b..e64417e1a4a 100644 --- a/compiler/rustc_codegen_ssa/src/traits/type_.rs +++ b/compiler/rustc_codegen_ssa/src/traits/type_.rs @@ -126,6 +126,28 @@ pub trait LayoutTypeMethods<'tcx>: Backend<'tcx> { index: usize, immediate: bool, ) -> Self::Type; + + /// A type that can be used in a [`super::BuilderMethods::load`] + + /// [`super::BuilderMethods::store`] pair to implement a *typed* copy, + /// such as a MIR `*_0 = *_1`. + /// + /// It's always legal to return `None` here, as the provided impl does, + /// in which case callers should use [`super::BuilderMethods::memcpy`] + /// instead of the `load`+`store` pair. + /// + /// This can be helpful for things like arrays, where the LLVM backend type + /// `[3 x i16]` optimizes to three separate loads and stores, but it can + /// instead be copied via an `i48` that stays as the single `load`+`store`. + /// (As of 2023-05 LLVM cannot necessarily optimize away a `memcpy` in these + /// cases, due to `poison` handling, but in codegen we have more information + /// about the type invariants, so can emit something better instead.) + /// + /// This *should* return `None` for particularly-large types, where leaving + /// the `memcpy` may well be important to avoid code size explosion. + fn scalar_copy_backend_type(&self, layout: TyAndLayout<'tcx>) -> Option { + let _ = layout; + None + } } // For backends that support CFI using type membership (i.e., testing whether a given pointer is -- cgit 1.4.1-3-g733a5