| Issue |
140100
|
| Summary |
Missed VRP with __builtin_popcount() when bitshift with __builtin_{ctzg, clzg}
|
| Labels |
|
| Assignees |
|
| Reporter |
BreadTom
|
[Godbolt](https://godbolt.org/z/Ybco775zT)
[GCC bug](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120296)
```
extern void f0_unreachable(void);
void f0(unsigned int arg0, unsigned char arg1){
int tmp0;
unsigned int tmp1;
int tmp2[2];
if(arg1){
tmp0 = __builtin_ctzg(arg0, 0);
tmp1 = arg0 >> tmp0;
} else {
tmp0 = __builtin_clzg(arg0, 0);
tmp1 = arg0 << tmp0;
}
tmp2[0] = __builtin_popcount(arg0);
tmp2[1] = __builtin_popcount(tmp1);
if(tmp2[0] != tmp2[1])
f0_unreachable();
}
```
When bitshifting ARG0 till it reaches one (or zero if it is zero), popcount should remain same and should not execute f0_unreachable() with flags -O3 -march=icelake-client.
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