[PATCH] D67366: [CGP] Ensure sinking multiple instructions does not invalidate dominance checks

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: fhahn, samparker, samtebbs, efriedma.
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In MVE, as of rL371218 <https://reviews.llvm.org/rL371218>, we are attempting to sink chains of instructions such as:

  %l1 = insertelement <8 x i8> undef, i8 %l0, i32 0
  %broadcast.splat26 = shufflevector <8 x i8> %l1, <8 x i8> undef, <8 x i32> zeroinitializer

In certain situations though, we can end up breaking the dominance relations of instructions. This happens when we sink the instruction into a loop, but cannot remove the originals. The Use is updated, which might in fact be a Use from the second instruction to the first.

This attempts to fix that by reversing the order of instruction that are sunk, and ensuring that we update the uses on new instructions if they have already been sunk, not the old ones.


https://reviews.llvm.org/D67366

Files:
  llvm/lib/CodeGen/CodeGenPrepare.cpp
  llvm/test/Transforms/CodeGenPrepare/ARM/sink-add-mul-shufflevector.ll
  llvm/test/Transforms/CodeGenPrepare/ARM/sinkchain.ll

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