Optimize DST field access #80200
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Optimize DST field access #80200
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For
struct X<T: ?Sized>(T)
struct Y<T: ?Sized>(u8, T)
the offset of the unsized field is
0
mem::align_of_val(&self.1)
respectively. This patch changes the expression used to compute these
offsets so that the optimizer can perform this optimization.
Consider
```rust
fn test(x: &X<dyn Any>) -> &dyn Any {
&x.0
}
```
Before:
```asm
test:
movq %rsi, %rdx
movq 16(%rsi), %rax
leaq -1(%rax), %rcx
negq %rax
andq %rcx, %rax
addq %rdi, %rax
retq
```
After:
```asm
test:
movq %rsi, %rdx
movq %rdi, %rax
retq
```
|
r? @davidtwco (rust-highfive has picked a reviewer for you, use r? to override) |
rust-highfive
added
the
S-waiting-on-review
|
r? @nagisa |
|
I'm sorry I missed this for so long – fell through cracks in my mail! Will take a look tomorrow. |
|
@bors r+ |
|
📌 Commit be15114 has been approved by |
bors
added
S-waiting-on-bors
|
@bors rollup=never |
|
☀️ Test successful - checks-actions |
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For
the offset of the unsized field is
respectively. This patch changes the expression used to compute these
offsets so that the optimizer can perform this optimization.
Consider
Before:
After: