use undef for uninitialized bytes in constants

2 files changed, 53 insertions, 2 deletions

diff --git a/src/test/codegen/consts.rs b/src/test/codegen/consts.rs
index 7f945299c22..e47a9f9ee20 100644
--- a/src/test/codegen/consts.rs
+++ b/src/test/codegen/consts.rs
@@ -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.rs b/src/test/codegen/uninit-consts.rs
new file mode 100644
index 00000000000..518bf7f451f
--- /dev/null
+++ b/src/test/codegen/uninit-consts.rs
@@ -0,0 +1,51 @@
+// compile-flags: -C no-prepopulate-passes
+
+// Check that we use undef (and not zero) for uninitialized bytes in constants.
+
+#![crate_type = "lib"]
+
+use std::mem::MaybeUninit;
+
+pub struct PartiallyUninit {
+    x: u32,
+    y: MaybeUninit<[u8; 10]>
+}
+
+// CHECK: [[FULLY_UNINIT:@[0-9]+]] = private unnamed_addr constant <{ [10 x i8] }> 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
+// CHECK: [[FULLY_UNINIT_HUGE:@[0-9]+]] = private unnamed_addr constant <{ [16384 x i8] }> undef
+
+// This shouldn't contain undef, since generating huge partially undef constants is expensive.
+// CHECK: [[UNINIT_PADDING_HUGE:@[0-9]+]] = private unnamed_addr constant <{ [32768 x i8] }> <{ [32768 x i8] c"{{.+}}" }>, align 4
+
+// CHECK-LABEL: @fully_uninit
+#[no_mangle]
+pub const fn fully_uninit() -> MaybeUninit<[u8; 10]> {
+    const M: MaybeUninit<[u8; 10]> = MaybeUninit::uninit();
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 1 %1, i8* align 1 getelementptr inbounds (<{ [10 x i8] }>, <{ [10 x i8] }>* [[FULLY_UNINIT]], i32 0, i32 0, i32 0), i{{(32|64)}} 10, i1 false)
+    M
+}
+
+// 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: @fully_uninit_huge
+#[no_mangle]
+pub const fn fully_uninit_huge() -> MaybeUninit<[u32; 4096]> {
+    const F: MaybeUninit<[u32; 4096]> = MaybeUninit::uninit();
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [16384 x i8] }>, <{ [16384 x i8] }>* [[FULLY_UNINIT_HUGE]], i32 0, i32 0, i32 0), i{{(32|64)}} 16384, i1 false)
+    F
+}
+
+// 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
+}