| Issue |
162717
|
| Summary |
Failure to match signed sub overflow test idiom
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
sh1boot
|
Checking for signed integer overflow after an addItion seems to work fine, but this subtraction test gives bad code on multiple architectures (every one I tried, both 32-bit and 64-bit):
```c++
bool idiomatic_check_sub(int x, int y) {
int64_t result = int64_t(x) - int64_t(y);
return !(INT_MIN <= result && result <= INT_MAX);
}
bool expected_check_sub(int x, int y) {
int result;
return __builtin_ssub_overflow(x, y, &result);
}
```
https://godbolt.org/z/a91sjPzGz
I haven't checked but this issue may generalise across overflow tests for multiple destination data types. And presumably there's another pattern which people would use when there's no larger temporary type, but I have tested any of those yet.
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