| Issue |
208221
|
| Summary |
Performance regression from defining signed int overflow in -fms-compatibility mode
|
| Labels |
clang:codegen,
llvm:optimizations,
regression:23
|
| Assignees |
|
| Reporter |
AaronBallman
|
From https://github.com/llvm/llvm-project/pull/198538#issuecomment-4909059362
Our downstream testing at Intel ran into some performance differences that seem to come from these changes. For example, some code can no longer be vectorized (https://godbolt.org/z/7oeETzfY6) because compiler is unable to form the trip count of the loop due to the -fwrapv behavior:
```cpp
int x[40];
void doit1(int l, int u) {
int i;
#pragma clang loop vectorize(assume_safety)
for (i = l; i < u; i+= 3) x[i] += 1;
}
```
We also saw an 18% performance regression in SPEC2026 benchmarks such as cpu2026ref 772.marian_r.
CC @pankaj-chawla
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