[llvm] [VPlan] Split out optimizeEVLMasks. NFC (PR #174925)

[Florian Hahn via llvm-commits]

================
@@ -2979,8 +2979,43 @@ static VPRecipeBase *optimizeMaskToEVL(VPValue *HeaderMask,
   return nullptr;
 }
 
-/// Replace recipes with their EVL variants.
-static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
+/// Optimize away any EVL-based header masks to VP intrinsic based recipes.
+/// The transforms here need to preserve the original semantics.
+void VPlanTransforms::optimizeEVLMasks(VPlan &Plan) {
+  // Find the EVL-based header mask if it exists: icmp ult step-vector, EVL
+  VPValue *HeaderMask = nullptr, *EVL = nullptr;
+  for (VPRecipeBase &R : *Plan.getVectorLoopRegion()->getEntryBasicBlock()) {
+    if (match(&R, m_SpecificICmp(CmpInst::ICMP_ULT, m_StepVector(),
+                                 m_VPValue(EVL))) &&
+        match(EVL, m_EVL(m_VPValue()))) {
+      HeaderMask = R.getVPSingleValue();
+      break;
+    }
+  }
+  if (!HeaderMask)
+    return;
+
+  VPTypeAnalysis TypeInfo(Plan);
+  SmallVector<VPRecipeBase *> OldRecipes;
+  for (VPUser *U : collectUsersRecursively(HeaderMask)) {
+    VPRecipeBase *R = cast<VPRecipeBase>(U);
+    if (auto *NewR = optimizeMaskToEVL(HeaderMask, *R, TypeInfo, *EVL)) {
+      NewR->insertBefore(R);
+      for (auto [Old, New] :
+           zip_equal(R->definedValues(), NewR->definedValues()))
+        Old->replaceAllUsesWith(New);
+      OldRecipes.push_back(R);
+    }
+  }
+  // Erase recipes at the end so we don't invalidate TypeInfo.
+  for (VPRecipeBase *OldR : OldRecipes)
+    OldR->eraseFromParent();
+  removeDeadRecipes(Plan);
+}
+
+/// After replacing the IV with a EVL-based IV, fixup recipes that use VF to use
----------------
fhahn wrote:

```suggestion
/// After replacing the canonical IV with a EVL-based IV, fixup recipes that use VF to use
```

https://github.com/llvm/llvm-project/pull/174925