[llvm] [VPlan] Fold common edges away in convertPhisToBlends (PR #150368)

[Ramkumar Ramachandra via llvm-commits]

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@@ -227,6 +232,20 @@ void VPPredicator::createSwitchEdgeMasks(VPInstruction *SI) {
   setEdgeMask(Src, DefaultDst, DefaultMask);
 }
 
+VPValue *VPPredicator::findCommonEdgeMask(const VPWidenPHIRecipe *PhiR) const {
+  using namespace llvm::VPlanPatternMatch;
+  VPValue *EdgeMask = getEdgeMask(PhiR->getIncomingBlock(0), PhiR->getParent());
+  VPValue *CommonEdgeMask;
+  if (!EdgeMask ||
+      !match(EdgeMask, m_LogicalAnd(m_VPValue(CommonEdgeMask), m_VPValue())))
+    return nullptr;
+  for (unsigned In = 1; In < PhiR->getNumIncoming(); In++)
+    if (!match(getEdgeMask(PhiR->getIncomingBlock(In), PhiR->getParent()),
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artagnon wrote:

If getEdgeMask of PhiR's 0'th incoming block isn't nullptr (can it be nullptr?), are we guaranteed that all the other incoming blocks' edge masks aren't nullptr? Isn't getEdgeMask simply a lookup that may fail?

https://github.com/llvm/llvm-project/pull/150368