[llvm] [LV] Add support for partial alias masking with tail folding (PR #182457)

[Florian Hahn via llvm-commits]

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@@ -78,8 +79,15 @@ bool vputils::isHeaderMask(const VPValue *V, const VPlan &Plan) {
     return true;
   }
 
-  return match(V, m_ICmp(m_VPValue(A), m_VPValue(B))) && IsWideCanonicalIV(A) &&
-         B == Plan.getBackedgeTakenCount();
+  if (match(V, m_ICmp(m_VPValue(A), m_VPValue(B))) && IsWideCanonicalIV(A))
+    return B == Plan.getBackedgeTakenCount();
+
+  if (VPValue *AliasMask = findIncomingAliasMask(Plan)) {
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fhahn wrote:

do we need to find the alias mask or can we just check if it is an alias mask VPInstruction?

https://github.com/llvm/llvm-project/pull/182457