[llvm] [VPlan][Predicator] Simplify block mask by using PostDomFrontier (PR #186478)

[Luke Lau via llvm-commits]

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@@ -148,22 +151,25 @@ void VPPredicator::createBlockInMask(VPBasicBlock *VPBB) {
   // All-one mask is modelled as no-mask following the convention for masked
   // load/store/gather/scatter. Initialize BlockMask to no-mask.
   VPValue *BlockMask = nullptr;
-  // This is the block mask. We OR all unique incoming edges.
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lukel97 wrote:

Keep this comment and update it to say "This is the block mask. We OR all unique edges from the post-dominance frontier to successors that post-dominate VPBB."?

https://github.com/llvm/llvm-project/pull/186478