| Issue |
184729
|
| Summary |
Invalid min/max behavior with -O2 following #170223
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
rkirsling
|
As of https://github.com/llvm/llvm-project/pull/170223, finding the min and max positions of an array, as in [CppPerformanceBenchmark's minmax_sequence.cpp](https://gitlab.com/chriscox/CppPerformanceBenchmarks/-/blob/master/minmax_sequence.cpp), can produce invalid results with `-O2`.
In the context of that benchmark, we see numerous lines of the following sort...
```
test int8_t minmax position sequence2 failed (got 4346 instead of 45)
```
...in which an invalid position has been found for the minimum element.
---
Here is a reduced repro case:
https://godbolt.org/z/xeE3PxoqY
It shouldn't be architecture-specific, but repro is quite sensitive:
- we must calculate the min and max positions together in a single loop, and use both of these
- we must _not_ use the actual min and max values
- we must not hard-code the array
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