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Auto merge of #121298 - nikic:writable, r=cuviper

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Set writable and dead_on_unwind attributes for sret arguments

Set the `writable` and `dead_on_unwind` attributes for `sret` arguments. This allows call slot optimization to remove more memcpy's.

See https://llvm.org/docs/LangRef.html#parameter-attributes for the specification of these attributes. In short, the statement we're making here is that:

 * The return slot is writable.
 * The return slot will not be read if the function unwinds.

Fixes https://github.com/rust-lang/rust/issues/90595.
This commit is contained in:
bors 2024-04-25 04:31:56 +00:00
commit 284f94f9c0
7 changed files with 33 additions and 4 deletions
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2
tests/codegen/function-arguments.rs
View file

@ -197,7 +197,7 @@ pub fn notunpin_box(x: Box<NotUnpin>) -> Box<NotUnpin> {
x
}
// CHECK: @struct_return(ptr noalias nocapture noundef sret([32 x i8]) align 4 dereferenceable(32){{( %_0)?}})
// CHECK: @struct_return(ptr{{( dead_on_unwind)?}} noalias nocapture noundef{{( writable)?}} sret([32 x i8]) align 4 dereferenceable(32){{( %_0)?}})
#[no_mangle]
pub fn struct_return() -> S {
S {

2
tests/codegen/loongarch-abi/loongarch64-lp64d-abi.rs
View file

@ -260,7 +260,7 @@ pub struct IntDoubleInt {
#[no_mangle]
pub extern "C" fn f_int_double_int_s_arg(a: IntDoubleInt) {}
// CHECK: define void @f_ret_int_double_int_s(ptr noalias nocapture noundef sret([24 x i8]) align 8 dereferenceable(24) %_0)
// CHECK: define void @f_ret_int_double_int_s(ptr{{( dead_on_unwind)?}} noalias nocapture noundef{{( writable)?}} sret([24 x i8]) align 8 dereferenceable(24) %_0)
#[no_mangle]
pub extern "C" fn f_ret_int_double_int_s() -> IntDoubleInt {
IntDoubleInt { a: 1, b: 2., c: 3 }

6
tests/codegen/maybeuninit-rvo.rs
View file

@ -1,4 +1,6 @@
//@ compile-flags: -O
//@ needs-unwind
//@ min-llvm-version: 18
#![feature(c_unwind)]
#![crate_type = "lib"]
@ -23,8 +25,8 @@ extern "C-unwind" {
}
pub fn new_from_uninit_unwind() -> Foo {
// CHECK-LABEL: new_from_uninit
// CHECK: call void @llvm.memcpy.
// CHECK-LABEL: new_from_uninit_unwind
// CHECK-NOT: call void @llvm.memcpy.
let mut x = std::mem::MaybeUninit::uninit();
unsafe {
init_unwind(x.as_mut_ptr());