https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122385
Bug ID: 122385
Summary: (x == 0 || y == 0) can optimize to (x * y == 0) for
small integers in -Oz mode
Product: gcc
Version: 15.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: Explorer09 at gmail dot com
Target Milestone: ---
This is an optimization feature request.
If the integers a and b are so small that (a * b) (the multiplication) cannot
overflow, then (a == 0 || b == 0) can convert to (a * b == 0) for smaller code
size.
Because it's significantly slower to use multiplication in place of logical
checks, I expect this optimization be performed only in -Oz mode.
Architectures that I know can benefit from this optimization include: x86-64
and RISCV64.
```c
#include <stdbool.h>
#include <stdint.h>
bool func1(uint8_t a, uint8_t b, uint8_t c, uint8_t d) {
return a == 0 || b == 0 || c == 0 || d == 0;
}
bool func2(uint8_t a, uint8_t b, uint8_t c, uint8_t d) {
if (a == 0)
return true;
if (b == 0)
return true;
if (c == 0)
return true;
return d == 0;
}
bool func3(uint8_t a, uint8_t b, uint8_t c, uint8_t d) {
return ((uint32_t)a * b * c * d) == 0;
}
```
https://godbolt.org/z/sWYK89W1W
(This feature request was originally reported in Clang, but I think GCC could
also implement this feature.)
