| Issue |
131056
|
| Summary |
[Clang] Missed optimization within bitshift on bools
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
BreadTom
|
C code:
func1 only differs by using another bool from comparison of (ptr[n] == '_').
Otherwise, they should behave exactly the same.
```
#include <stdbool.h>
#include <stddef.h>
unsigned long func0(unsigned char * restrict ptr){
unsigned long ret_val = 0;
bool tmp_bool = false;
for(size_t n = 0; n < 64; n++){
tmp_bool = (ptr[n] == '_') || (ptr[n] >= 'a' && ptr[n] <= 'z') || (ptr[n] >= 'A' && ptr[n] <= 'Z') || (ptr[n] >= '0' && ptr[n] <= '9');
ret_val |= ((unsigned long)tmp_bool << n);
tmp_bool = false;
}
return ret_val;
}
unsigned long func1(unsigned char * restrict ptr){
unsigned long ret_val = 0;
bool tmp_bool = false;
bool tmp_bool1 = false;
for(size_t n = 0; n < 64; n++){
tmp_bool1 = ptr[n] == '_';
tmp_bool = tmp_bool || (ptr[n] >= 'a' && ptr[n] <= 'z') || (ptr[n] >= 'A' && ptr[n] <= 'Z') || (ptr[n] >= '0' && ptr[n] <= '9');
ret_val |= ((unsigned long)(tmp_bool || tmp_bool1) << n);
tmp_bool = false;
tmp_bool1 = false;
}
return ret_val;
}
```
[Godbolt](https://godbolt.org/z/xx6q4abjs) show that func1 reduces instructions by 101 compared to func0.
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