| Issue |
115252
|
| Summary |
Missed strict aliasing optimization between structs with similar layouts
|
| Labels |
enhancement,
c,
TBAA
|
| Assignees |
|
| Reporter |
PiJoules
|
Given this example:
```
typedef struct {
int i1;
} s1;
typedef struct {
int i1;
} s2_alt;
int f2(s1 *s1p, s2_alt *s2p) {
s1p->i1 = 2;
s2p->i1 = 3;
return s1p->i1 * 3;
}
```
I *think* strict aliasing rules in C should indicate that pointers to `s1` and `s2` shouldn't alias and `f2` can just directly return 6. ToT clang doesn't seem to be doing that (compiling with `-O3 -fstrict-aliasing`):
```
f2:
mov dword ptr [rdi], 2
mov dword ptr [rsi], 3
mov eax, dword ptr [rdi]
lea eax, [rax + 2*rax]
ret
```
whereas ToT gcc seems to give
```
f2:
mov DWORD PTR [rdi], 2
mov eax, 6
mov DWORD PTR [rsi], 3
ret
```
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