[PATCH] D86460: [InstCombine] improve demanded element analysis for insert-of-extract

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: aqjune, lebedev.ri, RKSimon, efriedma.
Herald added subscribers: hiraditya, mcrosier.
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spatel requested review of this revision.

InstCombine currently has odd rules for folding insert-extract chains to shuffles, so we miss collapsing seemingly simple cases as shown in the tests here.

But poison makes this not quite as easy as we might have guessed. Alive2 tests to show the subtle difference (similar to the regression tests):
https://alive2.llvm.org/ce/z/hp4hv3 (this is ok)
https://alive2.llvm.org/ce/z/ehEWaN (poison leakage)

SLP tends to create these patterns (as shown in the SLP tests), and this could help with solving PR16739.


https://reviews.llvm.org/D86460

Files:
  llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
  llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
  llvm/test/Transforms/SLPVectorizer/AArch64/getelementptr.ll
  llvm/test/Transforms/SLPVectorizer/X86/operandorder.ll

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