[all-commits] [llvm/llvm-project] c2c1e6: [VPlan] Replace disjoint or with add instead of dr...

[Florian Hahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c2c1e6ee4ce0df3d000ba880fa6cf58441da6462
      https://github.com/llvm/llvm-project/commit/c2c1e6ee4ce0df3d000ba880fa6cf58441da6462
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2024-03-19 (Tue, 19 Mar 2024)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h
    M llvm/lib/Transforms/Vectorize/VPlan.h
    M llvm/lib/Transforms/Vectorize/VPlanPatternMatch.h
    M llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
    M llvm/test/Transforms/LoopVectorize/X86/pr81872.ll

  Log Message:
  -----------
  [VPlan] Replace disjoint or with add instead of dropping disjoint. (#83821)

Dropping disjoint from an OR may yield incorrect results, as some
analysis may have converted it to an Add implicitly (e.g. SCEV used for
dependence analysis). Instead, replace it with an equivalent Add.

This is possible as all users of the disjoint OR only access lanes where
the operands are disjoint or poison otherwise.

Note that replacing all disjoint ORs with ADDs instead of dropping the
flags is not strictly necessary. It is only needed for disjoint ORs that
SCEV treated as ADDs, but those are not tracked.

There are other places that may drop poison-generating flags; those
likely need similar treatment.

Fixes https://github.com/llvm/llvm-project/issues/81872


PR: https://github.com/llvm/llvm-project/pull/83821



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