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Forward the ABI of the non-zero sized fields of an union if they have the same ABI
This is supposed to fix the performence regression of using MaybeUninit in https://github.com/rust-lang/rust/pull/54668
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@ -697,7 +697,9 @@ impl<'a, 'tcx> LayoutCx<'tcx, TyCtxt<'a, 'tcx, 'tcx>> {
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Align::from_bytes(repr_align, repr_align).unwrap());
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}
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let optimize = !def.repr.inhibit_union_abi_opt();
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let mut size = Size::ZERO;
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let mut abi = Abi::Aggregate { sized: true };
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let index = VariantIdx::new(0);
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for field in &variants[index] {
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assert!(!field.is_unsized());
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@ -708,13 +710,44 @@ impl<'a, 'tcx> LayoutCx<'tcx, TyCtxt<'a, 'tcx, 'tcx>> {
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} else {
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align = align.max(field.align);
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}
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// If all non-ZST fields have the same ABI, forward this ABI
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if optimize && !field.is_zst() {
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// Normalize scalar_unit to the maximal valid range
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let field_abi = match &field.abi {
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Abi::Scalar(x) => Abi::Scalar(scalar_unit(x.value)),
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Abi::ScalarPair(x, y) => {
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Abi::ScalarPair(
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scalar_unit(x.value),
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scalar_unit(y.value),
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)
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}
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Abi::Vector { element: x, count } => {
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Abi::Vector {
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element: scalar_unit(x.value),
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count: *count,
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}
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}
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Abi::Uninhabited |
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Abi::Aggregate { .. } => Abi::Aggregate { sized: true },
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};
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if size == Size::ZERO {
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// first non ZST: initialize 'abi'
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abi = field_abi;
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} else if abi != field_abi {
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// different fields have different ABI: reset to Aggregate
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abi = Abi::Aggregate { sized: true };
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}
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}
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size = cmp::max(size, field.size);
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}
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return Ok(tcx.intern_layout(LayoutDetails {
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variants: Variants::Single { index },
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fields: FieldPlacement::Union(variants[index].len()),
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abi: Abi::Aggregate { sized: true },
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abi,
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align,
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size: size.abi_align(align)
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}));
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@ -1994,6 +1994,12 @@ impl ReprOptions {
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pub fn inhibit_struct_field_reordering_opt(&self) -> bool {
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!(self.flags & ReprFlags::IS_UNOPTIMISABLE).is_empty() || (self.pack == 1)
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}
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/// Returns true if this `#[repr()]` should inhibit union abi optimisations
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pub fn inhibit_union_abi_opt(&self) -> bool {
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self.c()
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}
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}
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impl<'a, 'gcx, 'tcx> AdtDef {
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80
src/test/codegen/union-abi.rs
Normal file
80
src/test/codegen/union-abi.rs
Normal file
@ -0,0 +1,80 @@
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// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// compile-flags: -C no-prepopulate-passes
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// This test that using union forward the abi of the inner type, as
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// discussed in #54668
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#![crate_type="lib"]
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#![feature(repr_simd)]
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#[derive(Copy, Clone)]
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pub enum Unhab {}
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#[repr(simd)]
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#[derive(Copy, Clone)]
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pub struct i64x4(i64, i64, i64, i64);
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#[derive(Copy, Clone)]
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pub union UnionI64x4{ a:(), b: i64x4 }
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// CHECK: define <4 x i64> @test_UnionI64x4(<4 x i64> %arg0)
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#[no_mangle]
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pub extern fn test_UnionI64x4(_: UnionI64x4) -> UnionI64x4 { loop {} }
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pub union UnionI64x4_{ a: i64x4, b: (), c:i64x4, d: Unhab, e: ((),()), f: UnionI64x4 }
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// CHECK: define <4 x i64> @test_UnionI64x4_(<4 x i64> %arg0)
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#[no_mangle]
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pub extern fn test_UnionI64x4_(_: UnionI64x4_) -> UnionI64x4_ { loop {} }
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pub union UnionI64x4I64{ a: i64x4, b: i64 }
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// CHECK: define void @test_UnionI64x4I64(%UnionI64x4I64* {{.*}} %arg0)
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#[no_mangle]
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pub fn test_UnionI64x4I64(_: UnionI64x4I64) { loop {} }
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pub union UnionI64x4Tuple{ a: i64x4, b: (i64, i64, i64, i64) }
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// CHECK: define void @test_UnionI64x4Tuple(%UnionI64x4Tuple* {{.*}} %arg0)
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#[no_mangle]
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pub fn test_UnionI64x4Tuple(_: UnionI64x4Tuple) { loop {} }
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pub union UnionF32{a:f32}
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// CHECK: define float @test_UnionF32(float %arg0)
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#[no_mangle]
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pub extern fn test_UnionF32(_: UnionF32) -> UnionF32 { loop {} }
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pub union UnionF32F32{a:f32, b:f32}
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// CHECK: define float @test_UnionF32F32(float %arg0)
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#[no_mangle]
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pub extern fn test_UnionF32F32(_: UnionF32F32) -> UnionF32F32 { loop {} }
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pub union UnionF32U32{a:f32, b:u32}
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// CHECK: define i32 @test_UnionF32U32(i32)
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#[no_mangle]
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pub extern fn test_UnionF32U32(_: UnionF32U32) -> UnionF32U32 { loop {} }
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pub union UnionU128{a:u128}
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// CHECK: define i128 @test_UnionU128(i128 %arg0)
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#[no_mangle]
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pub fn test_UnionU128(_: UnionU128) -> UnionU128 { loop {} }
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#[repr(C)]
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pub union CUnionU128{a:u128}
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// CHECK: define void @test_CUnionU128(%CUnionU128* {{.*}} %arg0)
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#[no_mangle]
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pub fn test_CUnionU128(_: CUnionU128) { loop {} }
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