[llvm] [VPlan] Simplify the computation of the block entry mask. (PR #173265)

[Luke Lau via llvm-commits]

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@@ -127,15 +133,33 @@ VPValue *VPPredicator::createEdgeMask(VPBasicBlock *Src, VPBasicBlock *Dst) {
 }
 
 void VPPredicator::createBlockInMask(VPBasicBlock *VPBB) {
-  // Start inserting after the block's phis, which be replaced by blends later.
+  // Compute the edge masks for all incoming edges to VPBB. Insert after the
+  // block's phis, which will be replaced by blends later.
+  // TODO: Skip creating edge masks for blocks that are control-flow equivalent
+  // to header and have no phis.
   Builder.setInsertPoint(VPBB, VPBB->getFirstNonPhi());
+  for (auto *Predecessor : SetVector<VPBlockBase *>(
+           VPBB->getPredecessors().begin(), VPBB->getPredecessors().end()))
+    createEdgeMask(cast<VPBasicBlock>(Predecessor), VPBB);
+
+  // Reuse the mask of header block if VPBB is control-flow equivalent to
+  // header.
+  // TODO: Generalize to reuse mask of immediate dominator.
+  VPBasicBlock *Header =
+      VPBB->getPlan()->getVectorLoopRegion()->getEntryBasicBlock();
+  if (VPPDT.properlyDominates(VPBB, Header)) {
+    setBlockInMask(VPBB, getBlockInMask(Header));
+    return;
+  }
+
   // 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;
+
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lukel97 wrote:

Nit stray whitespace change

https://github.com/llvm/llvm-project/pull/173265