| Issue |
204074
|
| Summary |
Possible Missed Optimization at O3
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
Apochens
|
Reproducer: https://godbolt.org/z/TbTMr1Tnx
Description: LLVM (trunk -O3) cannot optimize the following C function annotated with value range information, while GCC (trunk -O3) can.
```c
int src(unsigned v1_u8, int v3_i8) {
if (!((1 <= v1_u8) && (v1_u8 <= 2))) __builtin_unreachable();
if (!((6 <= v3_i8) && (v3_i8 <= 7))) __builtin_unreachable();
int i0_i8 = v3_i8 >> v1_u8;
int i1_i8 = v3_i8 | i0_i8;
return i1_i8;
}
```
Clang at O3:
```assembly
src:
mov ecx, edi
mov eax, esi
shr eax, cl
or eax, esi
ret
```
GCC at O3:
```assembly
"src":
mov eax, 7
ret
```
![]()
_______________________________________________
llvm-bugs mailing list
[email protected]
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
