| Issue |
143267
|
| Summary |
Missing optimization: loop invariant memset should be hoisted if it's the only memory access in loop
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
WanderingAura
|
Currently memset is unrolled and optimized within the body of the loop instead of being hoisted, which is suboptimal when the unrolling is less than the iteration number: https://godbolt.org/z/dK3a7xjPW.
This also means -fno-unroll-loops causes the memsets to not be optimized at all.
Previously discussed in https://github.com/llvm/llvm-project/issues/143015:
> The optimization happens as a result of unrolling, so it is affected by target-dependent heuristics. It would be legal to do it independently of unrolling by hoisting the memset out of the loop, it's just not implemented. It does work for a plain store, implemented here I believe: https://github.com/llvm/llvm-project/blob/470f456567fb6c6ee8b6e51c06a64536ca076d74/llvm/lib/Transforms/Scalar/LICM.cpp#L1269 It could be extended to the memset case.
_Originally posted by @nikic in [#143015](https://github.com/llvm/llvm-project/issues/143015#issuecomment-2948480418)_
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