https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115636
Bug ID: 115636
Summary: Missing optimzation: fold ` (w << (unsigned int)((flag
? a : b) - 32768))` to ` flag ? w << (unsigned int)(a
- 32768) : 0 `
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: zhiwuyazhe154 at gmail dot com
Target Milestone: ---
godbolt example: https://godbolt.org/z/W5hr6G8oK
code example:
```cpp
short b, n;
void func(signed char w, signed char flag, unsigned long long int a) {
n = 0 >= (w << (unsigned int)((flag ? a : b) - 32768));
}
```
In this case, when flag != 0, no matter what the value of b is, the value of
(unsigned int)(b - 32768) is much greater than 8, which means that w will be
shifted left more than 8 times. According to the behavior of gcc, the value of
w will be assigned to 0, that is, as long as flag != 0, then w will be 0,
regardless of the value of b.
