[llvm] [VPlan] Move addExplicitVectorLength to tryToBuildVPlanWithVPRecipes (PR #166164)

[Luke Lau via llvm-commits]

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@@ -2617,8 +2621,40 @@ static VPRecipeBase *optimizeMaskToEVL(VPValue *HeaderMask,
   return nullptr;
 }
 
-/// Replace recipes with their EVL variants.
-static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
+void VPlanTransforms::optimizeMasksToEVL(VPlan &Plan) {
+  // Find the EVL-based header mask if it exists: icmp ult step-vector, EVL
+  VPInstruction *HeaderMask = nullptr;
+  for (VPRecipeBase &R : *Plan.getVectorLoopRegion()->getEntryBasicBlock()) {
+    if (match(&R, m_ICmp(m_VPInstruction<VPInstruction::StepVector>(),
+                         m_EVL(m_VPValue())))) {
+      HeaderMask = cast<VPInstruction>(&R);
+      break;
+    }
+  }
+  if (!HeaderMask)
+    return;
+
+  VPValue *EVL = HeaderMask->getOperand(1);
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lukel97 wrote:

I wasn't planning on creating a helper function. I think the change you suggested matches the AVL though, not the EVL. I think we need something like `bind_and_match_ty` from PatternMatch.h where we can both match and capture a value

https://github.com/llvm/llvm-project/pull/166164