[llvm] [VPlan] Iterate over header phis to determine FORs that need EVL fixup. NFCI (PR #147032)

[Florian Hahn via llvm-commits]

================
@@ -2187,42 +2187,48 @@ static void transformRecipestoEVLRecipes(VPlan &Plan, VPValue &EVL) {
   // VPTypeAnalysis cache.
   SmallVector<VPRecipeBase *> ToErase;
 
-  // Create a scalar phi to track the previous EVL if fixed-order recurrence is
-  // contained.
-  bool ContainsFORs =
-      any_of(Header->phis(), IsaPred<VPFirstOrderRecurrencePHIRecipe>);
-  if (ContainsFORs) {
-    // TODO: Use VPInstruction::ExplicitVectorLength to get maximum EVL.
-    VPValue *MaxEVL = &Plan.getVF();
-    // Emit VPScalarCastRecipe in preheader if VF is not a 32 bits integer.
-    VPBuilder Builder(LoopRegion->getPreheaderVPBB());
-    MaxEVL = Builder.createScalarZExtOrTrunc(MaxEVL, Type::getInt32Ty(Ctx),
-                                             TypeInfo.inferScalarType(MaxEVL),
-                                             DebugLoc());
-
-    Builder.setInsertPoint(Header, Header->getFirstNonPhi());
-    VPValue *PrevEVL =
-        Builder.createScalarPhi({MaxEVL, &EVL}, DebugLoc(), "prev.evl");
-
-    for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(
-             vp_depth_first_deep(Plan.getVectorLoopRegion()->getEntry()))) {
-      for (VPRecipeBase &R : *VPBB) {
-        using namespace VPlanPatternMatch;
-        VPValue *V1, *V2;
-        if (!match(&R,
-                   m_VPInstruction<VPInstruction::FirstOrderRecurrenceSplice>(
-                       m_VPValue(V1), m_VPValue(V2))))
-          continue;
-        VPValue *Imm = Plan.getOrAddLiveIn(
-            ConstantInt::getSigned(Type::getInt32Ty(Ctx), -1));
-        VPWidenIntrinsicRecipe *VPSplice = new VPWidenIntrinsicRecipe(
-            Intrinsic::experimental_vp_splice,
-            {V1, V2, Imm, AllOneMask, PrevEVL, &EVL},
-            TypeInfo.inferScalarType(R.getVPSingleValue()), R.getDebugLoc());
-        VPSplice->insertBefore(&R);
-        R.getVPSingleValue()->replaceAllUsesWith(VPSplice);
-        ToErase.push_back(&R);
-      }
+  // Fix-up first-order recurrences
+  VPValue *PrevEVL = nullptr;
+  for (VPRecipeBase &PhiR : Header->phis()) {
+    auto *FOR = dyn_cast<VPFirstOrderRecurrencePHIRecipe>(&PhiR);
+    if (!FOR)
+      continue;
+
+    // Create a scalar phi to track the previous EVL if fixed-order recurrence
+    // is contained.
+    if (!PrevEVL) {
+      // TODO: Use VPInstruction::ExplicitVectorLength to get maximum EVL.
+      VPValue *MaxEVL = &Plan.getVF();
+      // Emit VPScalarCastRecipe in preheader if VF is not a 32 bits integer.
+      VPBuilder Builder(LoopRegion->getPreheaderVPBB());
+      MaxEVL = Builder.createScalarZExtOrTrunc(MaxEVL, Type::getInt32Ty(Ctx),
+                                               TypeInfo.inferScalarType(MaxEVL),
+                                               DebugLoc());
+
+      Builder.setInsertPoint(Header, Header->getFirstNonPhi());
+      PrevEVL = Builder.createScalarPhi({MaxEVL, &EVL}, DebugLoc(), "prev.evl");
+    }
+
+    assert(!Plan.isUnrolled() && "When unrolled splices might not use "
+                                 "VPFirstOrederRecurrencePHIRecipe!");
+
+    for (VPUser *User : PhiR.getVPSingleValue()->users()) {
----------------
fhahn wrote:

```suggestion
    for (VPUser *User : FOR->users()) {
```

https://github.com/llvm/llvm-project/pull/147032