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

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

3 files changed, 20 insertions, 40 deletions

diff --git a/src/test/codegen/consts.rs b/src/test/codegen/consts.rs
index 7f945299c22..1a84f1a4479 100644
--- a/src/test/codegen/consts.rs
+++ b/src/test/codegen/consts.rs
@@ -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)
 }
diff --git a/src/test/codegen/uninit-consts-allow-partially-uninit.rs b/src/test/codegen/uninit-consts-allow-partially-uninit.rs
deleted file mode 100644
index f7420e4126e..00000000000
--- a/src/test/codegen/uninit-consts-allow-partially-uninit.rs
+++ /dev/null
@@ -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
-}
diff --git a/src/test/codegen/uninit-consts.rs b/src/test/codegen/uninit-consts.rs
index c4c21e03f16..3e370c7ba64 100644
--- a/src/test/codegen/uninit-consts.rs
+++ b/src/test/codegen/uninit-consts.rs
@@ -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
 }