Max Kazantsev comments

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                                            Max Kazantsev

[IndVars] Miscompile: UB introduced to a simple program by indvars

Please don't revert this patch, it's not guilty. I'll prepare a proper fix.

[IndVars] Miscompile: UB introduced to a simple program by indvars

The problematic instruction was hoisted from backedge to inside the loop by ``` NumElimIV += Rewriter.replaceCongruentIVs(L, DT, DeadInsts, TTI); ``` Guess this thing just doesn't take poison into account.

[IndVars] Miscompile: UB introduced to a simple program by indvars

On review: https://reviews.llvm.org/D132022

[IndVars] Miscompile: UB introduced to a simple program by indvars

``` commit 86d5586d78d813a6921d786f7ddb1a41c6fb56e0 (HEAD -> main, origin/main, origin/HEAD) Author: Max Kazantsev Date: Tue Sep 13 12:31:07 2022 +0700 [SCEVExpander] Recompute poison-generating flags on hoisting. PR57187 Instruction being hoisted could have...

[LoopVectorize] Clang fails to vectorize simple polynomial hash

Another (also pretty straightforward) version of same algorithm doesn't vectorize either: ``` unsigned rabin_karp_naive_v2(unsigned *s, unsigned len) { unsigned hash = 0; unsigned mul = 1; for (unsigned i =...