[all-commits] [llvm/llvm-project] 0dddf0: [LV] Don't optimize exit cond during epilogue vect...

[Florian Hahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0dddf04caba55a64f8534518d65311bdac05cf39
      https://github.com/llvm/llvm-project/commit/0dddf04caba55a64f8534518d65311bdac05cf39
  Author: Florian Hahn <flo at fhahn.com>
  Date:   2022-07-01 (Fri, 01 Jul 2022)

  Changed paths:
    M llvm/lib/Transforms/Vectorize/LoopVectorizationPlanner.h
    M llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
    M llvm/lib/Transforms/Vectorize/VPlan.cpp
    M llvm/lib/Transforms/Vectorize/VPlan.h
    M llvm/test/Transforms/LoopVectorize/X86/pr42674.ll
    M llvm/test/Transforms/LoopVectorize/X86/pr56319-vector-exit-cond-optimization-epilogue-vectorization.ll

  Log Message:
  -----------
  [LV] Don't optimize exit cond during epilogue vectorization.

At the moment, the same VPlan can be used code generation of both the
main vector and epilogue vector loop. This can lead to wrong results, if
the plan is optimized based on the VF of the main vector loop and then
re-used for the epilogue loop.

One example where this is problematic is if the scalar loops need to
execute at least one iteration, e.g. due to interleave groups.

To prevent mis-compiles in the short-term, disable optimizing exit
conditions for VPlans when using epilogue vectorization. The proper fix
is to avoid re-using the same plan for both loops, which will require
support for cloning plans first.

Fixes #56319.