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Rollup merge of #115096 - kadiwa4:no_memcpy_padding, r=cjgillot

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Add regression test for not `memcpy`ing padding bytes

Closes #56297

See this comparison: https://rust.godbolt.org/z/jjzfonfcE

I don't have any experience with codegen tests, I hope this is correct
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Dylan DPC 2023-08-23 05:35:17 +00:00 • committed by GitHub
commit 391cbdaa7c
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14
tests/codegen/box-maybe-uninit.rs → tests/codegen/box-uninit-bytes.rs
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@ -25,6 +25,20 @@ pub fn box_uninitialized2() -> Box<MaybeUninit<[usize; 1024 * 1024]>> {
Box::new(MaybeUninit::uninit())
}
#[repr(align(1024))]
pub struct LotsaPadding(usize);
// Boxing a value with padding should not copy junk from the stack
#[no_mangle]
pub fn box_lotsa_padding() -> Box<LotsaPadding> {
// CHECK-LABEL: @box_lotsa_padding
// CHECK-NOT: alloca
// CHECK-NOT: getelementptr
// CHECK-NOT: memcpy
// CHECK-NOT: memset
Box::new(LotsaPadding(42))
}
// Hide the `allocalign` attribute in the declaration of __rust_alloc
// from the CHECK-NOT above, and also verify the attributes got set reasonably.
// CHECK: declare {{(dso_local )?}}noalias noundef ptr @__rust_alloc(i{{[0-9]+}} noundef, i{{[0-9]+}} allocalign noundef) unnamed_addr [[RUST_ALLOC_ATTRS:#[0-9]+]]