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Auto merge of #94130 - erikdesjardins:partially, r=nikic

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Use undef for (some) partially-uninit constants

There needs to be some limit to avoid perf regressions on large arrays
with undef in each element (see comment in the code).

Fixes: #84565
Original PR: #83698

Depends on LLVM 14: #93577
This commit is contained in:
bors 2022-02-25 05:44:33 +00:00
commit ece55d416e
7 changed files with 44 additions and 66 deletions
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6
src/test/codegen/consts.rs
View file

@ -1,5 +1,5 @@
// compile-flags: -C no-prepopulate-passes
//
// min-llvm-version: 14.0
#![crate_type = "lib"]
@ -43,7 +43,7 @@ pub fn inline_enum_const() -> E<i8, i16> {
#[no_mangle]
pub fn low_align_const() -> E<i16, [i16; 3]> {
// Check that low_align_const and high_align_const use the same constant
// CHECK: memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 2 %1, i8* align 2 getelementptr inbounds (<{ [8 x i8] }>, <{ [8 x i8] }>* [[LOW_HIGH]], i32 0, i32 0, i32 0), i{{(32|64)}} 8, i1 false)
// CHECK: memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 2 %1, i8* align 2 getelementptr inbounds (<{ [4 x i8], [4 x i8] }>, <{ [4 x i8], [4 x i8] }>* [[LOW_HIGH]], i32 0, i32 0, i32 0), i{{(32|64)}} 8, i1 false)
*&E::A(0)
}
@ -51,6 +51,6 @@ pub fn low_align_const() -> E<i16, [i16; 3]> {
#[no_mangle]
pub fn high_align_const() -> E<i16, i32> {
// Check that low_align_const and high_align_const use the same constant
// CHECK: memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [8 x i8] }>, <{ [8 x i8] }>* [[LOW_HIGH]], i32 0, i32 0, i32 0), i{{(32|64)}} 8, i1 false)
// CHECK: memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [4 x i8], [4 x i8] }>, <{ [4 x i8], [4 x i8] }>* [[LOW_HIGH]], i32 0, i32 0, i32 0), i{{(32|64)}} 8, i1 false)
*&E::A(0)
}

35
src/test/codegen/uninit-consts-allow-partially-uninit.rs
View file

@ -1,35 +0,0 @@
// compile-flags: -C no-prepopulate-passes -Z partially_uninit_const_threshold=1024
// Like uninit-consts.rs, but tests that we correctly generate partially-uninit consts
// when the (disabled by default) partially_uninit_const_threshold flag is used.
#![crate_type = "lib"]
use std::mem::MaybeUninit;
pub struct PartiallyUninit {
x: u32,
y: MaybeUninit<[u8; 10]>
}
// This should be partially undef.
// CHECK: [[PARTIALLY_UNINIT:@[0-9]+]] = private unnamed_addr constant <{ [4 x i8], [12 x i8] }> <{ [4 x i8] c"\EF\BE\AD\DE", [12 x i8] undef }>, align 4
// This shouldn't contain undef, since it's larger than the 1024 byte limit.
// CHECK: [[UNINIT_PADDING_HUGE:@[0-9]+]] = private unnamed_addr constant <{ [32768 x i8] }> <{ [32768 x i8] c"{{.+}}" }>, align 4
// CHECK-LABEL: @partially_uninit
#[no_mangle]
pub const fn partially_uninit() -> PartiallyUninit {
const X: PartiallyUninit = PartiallyUninit { x: 0xdeadbeef, y: MaybeUninit::uninit() };
// CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [4 x i8], [12 x i8] }>, <{ [4 x i8], [12 x i8] }>* [[PARTIALLY_UNINIT]], i32 0, i32 0, i32 0), i{{(32|64)}} 16, i1 false)
X
}
// CHECK-LABEL: @uninit_padding_huge
#[no_mangle]
pub const fn uninit_padding_huge() -> [(u32, u8); 4096] {
const X: [(u32, u8); 4096] = [(123, 45); 4096];
// CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [32768 x i8] }>, <{ [32768 x i8] }>* [[UNINIT_PADDING_HUGE]], i32 0, i32 0, i32 0), i{{(32|64)}} 32768, i1 false)
X
}

19
src/test/codegen/uninit-consts.rs
View file

@ -1,4 +1,5 @@
// compile-flags: -C no-prepopulate-passes
// min-llvm-version: 14.0
// Check that we use undef (and not zero) for uninitialized bytes in constants.
@ -12,7 +13,13 @@ pub struct PartiallyUninit {
}
// CHECK: [[FULLY_UNINIT:@[0-9]+]] = private unnamed_addr constant <{ [10 x i8] }> undef
// CHECK: [[PARTIALLY_UNINIT:@[0-9]+]] = private unnamed_addr constant <{ [16 x i8] }> <{ [16 x i8] c"\EF\BE\AD\DE\00\00\00\00\00\00\00\00\00\00\00\00" }>, align 4
// CHECK: [[PARTIALLY_UNINIT:@[0-9]+]] = private unnamed_addr constant <{ [4 x i8], [12 x i8] }> <{ [4 x i8] c"\EF\BE\AD\DE", [12 x i8] undef }>, align 4
// This shouldn't contain undef, since it contains more chunks
// than the default value of uninit_const_chunk_threshold.
// CHECK: [[UNINIT_PADDING_HUGE:@[0-9]+]] = private unnamed_addr constant <{ [32768 x i8] }> <{ [32768 x i8] c"{{.+}}" }>, align 4
// CHECK: [[FULLY_UNINIT_HUGE:@[0-9]+]] = private unnamed_addr constant <{ [16384 x i8] }> undef
// CHECK-LABEL: @fully_uninit
@ -27,7 +34,15 @@ pub const fn fully_uninit() -> MaybeUninit<[u8; 10]> {
#[no_mangle]
pub const fn partially_uninit() -> PartiallyUninit {
const X: PartiallyUninit = PartiallyUninit { x: 0xdeadbeef, y: MaybeUninit::uninit() };
// CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [16 x i8] }>, <{ [16 x i8] }>* [[PARTIALLY_UNINIT]], i32 0, i32 0, i32 0), i{{(32|64)}} 16, i1 false)
// CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [4 x i8], [12 x i8] }>, <{ [4 x i8], [12 x i8] }>* [[PARTIALLY_UNINIT]], i32 0, i32 0, i32 0), i{{(32|64)}} 16, i1 false)
X
}
// CHECK-LABEL: @uninit_padding_huge
#[no_mangle]
pub const fn uninit_padding_huge() -> [(u32, u8); 4096] {
const X: [(u32, u8); 4096] = [(123, 45); 4096];
// CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [32768 x i8] }>, <{ [32768 x i8] }>* [[UNINIT_PADDING_HUGE]], i32 0, i32 0, i32 0), i{{(32|64)}} 32768, i1 false)
X
}