| commit | 6e1d94708a0a4a35ca7e46c6cac98adf62fe800e | [log] [tgz] |
|---|---|---|
| author | bors <bors@rust-lang.org> | Fri May 10 20:17:22 2024 +0000 |
| committer | bors <bors@rust-lang.org> | Fri May 10 20:17:22 2024 +0000 |
| tree | 9a8282ea1f9f07b94dccc143c778483f4758e5a2 | |
| parent | 2cce0885840cd171cb3a8677af795d0abd2dc77c [diff] | |
| parent | c38f75c21f016bffbf841ed5abce338f94201bde [diff] |
Auto merge of #123886 - scottmcm:more-rvalue-operands, r=matthewjasper
Avoid `alloca`s in codegen for simple `mir::Aggregate` statements
The core idea here is to remove the abstraction penalty of simple newtypes in codegen.
Even something simple like constructing a
```rust
#[repr(transparent)] struct Foo(u32);
```
forces an `alloca` to be generated in nightly right now.
Certainly LLVM can optimize that away, but it would be nice if it didn't have to.
Quick example:
```rust
#[repr(transparent)]
pub struct Transparent32(u32);
#[no_mangle]
pub fn make_transparent(x: u32) -> Transparent32 {
let a = Transparent32(x);
a
}
```
on nightly we produce <https://rust.godbolt.org/z/zcvoM79ae>
```llvm
define noundef i32 `@make_transparent(i32` noundef %x) unnamed_addr #0 {
%a = alloca i32, align 4
store i32 %x, ptr %a, align 4
%0 = load i32, ptr %a, align 4, !noundef !3
ret i32 %0
}
```
but after this PR we produce
```llvm
define noundef i32 `@make_transparent(i32` noundef %x) unnamed_addr #0 {
start:
ret i32 %x
}
```
(even before the optimizer runs).
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