| Issue |
91619
|
| Summary |
Missed optimization in bounds analysis in unsigned arithmetic that cannot underflow
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
davidben
|
Clang doesn't seem to be able to optimize the following out:
```
bool f(size_t a, size_t b) {
__builtin_assume(a <= b);
__builtin_assume(b <= PTRDIFF_MAX);
// This can be deleted, because:
// 1. 0 <= a <= b implies that b - a <= b
// 2. b - a <= b <= PTRDIFF_MAX
return b - a <= PTRDIFF_MAX;
}
```
https://godbolt.org/z/vzE7qb7Gb
I ran into this while exploring what combination of `__builtin_assume`s would dispatch some unnecessary assertions in `std::string_view`. (A separate bug while I'll file after this.)
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