[VPlan] Create resume phis in scalar preheader early. (NFC)

[fhahn]

Create phi recipes for scalar resume value up front in addInitialSkeleton during initial construction. This will allow moving the remaining code dealing with resume values to VPlan transforms/construction.

[llvmbot]

@llvm/pr-subscribers-vectorizers

@llvm/pr-subscribers-llvm-transforms

Author: Florian Hahn (fhahn)

Changes

Create phi recipes for scalar resume value up front in addInitialSkeleton during initial construction. This will allow moving the remaining code dealing with resume values to VPlan transforms/construction.

---

Full diff: https://github.com/llvm/llvm-project/pull/166099.diff

3 Files Affected:

• (modified) llvm/lib/Transforms/Vectorize/VPlan.h (+3-1)
• (modified) llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp (+9)
• (modified) llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp (+15-21)

diff --git a/llvm/lib/Transforms/Vectorize/VPlan.h b/llvm/lib/Transforms/Vectorize/VPlan.h
index aba6d351a8e5d..1aa1d0f894495 100644
--- a/llvm/lib/Transforms/Vectorize/VPlan.h
+++ b/llvm/lib/Transforms/Vectorize/VPlan.h
@@ -1079,7 +1079,7 @@ class LLVM_ABI_FOR_TEST VPInstruction : public VPRecipeWithIRFlags,
   OpcodeTy Opcode;
 
   /// An optional name that can be used for the generated IR instruction.
-  const std::string Name;
+  std::string Name;
 
   /// Returns true if we can generate a scalar for the first lane only if
   /// needed.
@@ -1179,6 +1179,8 @@ class LLVM_ABI_FOR_TEST VPInstruction : public VPRecipeWithIRFlags,
 
   /// Returns the symbolic name assigned to the VPInstruction.
   StringRef getName() const { return Name; }
+
+  void setName(StringRef NewName) { Name = NewName.str(); }
 };
 
 /// A specialization of VPInstruction augmenting it with a dedicated result
diff --git a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
index 1a66d2049a8db..8c65f5e2c8b18 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanConstruction.cpp
@@ -527,6 +527,15 @@ static void addInitialSkeleton(VPlan &Plan, Type *InductionTy, DebugLoc IVDL,
   Plan.getEntry()->swapSuccessors();
 
   createExtractsForLiveOuts(Plan, MiddleVPBB);
+
+  VPBuilder ScalarPHBuilder(ScalarPH);
+  for (const auto &[PhiR, ScalarPhiR] : zip_equal(
+           drop_begin(HeaderVPBB->phis()), Plan.getScalarHeader()->phis())) {
+    auto *VectorPhiR = cast<VPPhi>(&PhiR);
+    auto *ResumePhiR = ScalarPHBuilder.createScalarPhi(
+        {VectorPhiR, VectorPhiR->getOperand(0)}, VectorPhiR->getDebugLoc());
+    cast<VPIRPhi>(&ScalarPhiR)->addOperand(ResumePhiR);
+  }
 }
 
 std::unique_ptr<VPlan>
diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index f50bf29970597..6987dab35a4f4 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -4376,9 +4376,10 @@ void VPlanTransforms::addBranchWeightToMiddleTerminator(
 /// Create and return a ResumePhi for \p WideIV, unless it is truncated. If the
 /// induction recipe is not canonical, creates a VPDerivedIVRecipe to compute
 /// the end value of the induction.
-static VPInstruction *addResumePhiRecipeForInduction(
-    VPWidenInductionRecipe *WideIV, VPBuilder &VectorPHBuilder,
-    VPBuilder &ScalarPHBuilder, VPTypeAnalysis &TypeInfo, VPValue *VectorTC) {
+static VPValue *addResumePhiRecipeForInduction(VPWidenInductionRecipe *WideIV,
+                                               VPBuilder &VectorPHBuilder,
+                                               VPTypeAnalysis &TypeInfo,
+                                               VPValue *VectorTC) {
   auto *WideIntOrFp = dyn_cast<VPWidenIntOrFpInductionRecipe>(WideIV);
   // Truncated wide inductions resume from the last lane of their vector value
   // in the last vector iteration which is handled elsewhere.
@@ -4404,9 +4405,7 @@ static VPInstruction *addResumePhiRecipeForInduction(
                                                 WideIV->getDebugLoc());
   }
 
-  auto *ResumePhiRecipe = ScalarPHBuilder.createScalarPhi(
-      {EndValue, Start}, WideIV->getDebugLoc(), "bc.resume.val");
-  return ResumePhiRecipe;
+  return EndValue;
 }
 
 void VPlanTransforms::addScalarResumePhis(
@@ -4419,21 +4418,18 @@ void VPlanTransforms::addScalarResumePhis(
   VPBuilder VectorPHBuilder(
       cast<VPBasicBlock>(VectorRegion->getSinglePredecessor()));
   VPBuilder MiddleBuilder(MiddleVPBB, MiddleVPBB->getFirstNonPhi());
-  VPBuilder ScalarPHBuilder(ScalarPH);
-  for (VPRecipeBase &ScalarPhiR : Plan.getScalarHeader()->phis()) {
-    auto *ScalarPhiIRI = cast<VPIRPhi>(&ScalarPhiR);
+  for (VPRecipeBase &PhiR : Plan.getScalarPreheader()->phis()) {
+    auto *ResumePhiR = cast<VPPhi>(&PhiR);
 
     // TODO: Extract final value from induction recipe initially, optimize to
     // pre-computed end value together in optimizeInductionExitUsers.
-    auto *VectorPhiR =
-        cast<VPHeaderPHIRecipe>(Builder.getRecipe(&ScalarPhiIRI->getIRPhi()));
+    auto *VectorPhiR = cast<VPHeaderPHIRecipe>(ResumePhiR->getOperand(0));
     if (auto *WideIVR = dyn_cast<VPWidenInductionRecipe>(VectorPhiR)) {
-      if (VPInstruction *ResumePhi = addResumePhiRecipeForInduction(
-              WideIVR, VectorPHBuilder, ScalarPHBuilder, TypeInfo,
-              &Plan.getVectorTripCount())) {
-        assert(isa<VPPhi>(ResumePhi) && "Expected a phi");
-        IVEndValues[WideIVR] = ResumePhi->getOperand(0);
-        ScalarPhiIRI->addOperand(ResumePhi);
+      if (VPValue *ResumeV = addResumePhiRecipeForInduction(
+              WideIVR, VectorPHBuilder, TypeInfo, &Plan.getVectorTripCount())) {
+        IVEndValues[WideIVR] = ResumeV;
+        ResumePhiR->setOperand(0, ResumeV);
+        ResumePhiR->setName("bc.resume.val");
         continue;
       }
       // TODO: Also handle truncated inductions here. Computing end-values
@@ -4455,10 +4451,8 @@ void VPlanTransforms::addScalarResumePhis(
       ResumeFromVectorLoop = MiddleBuilder.createNaryOp(
           VPInstruction::ExtractLastElement, {ResumeFromVectorLoop}, {},
           "vector.recur.extract");
-    StringRef Name = IsFOR ? "scalar.recur.init" : "bc.merge.rdx";
-    auto *ResumePhiR = ScalarPHBuilder.createScalarPhi(
-        {ResumeFromVectorLoop, VectorPhiR->getStartValue()}, {}, Name);
-    ScalarPhiIRI->addOperand(ResumePhiR);
+    ResumePhiR->setName(IsFOR ? "scalar.recur.init" : "bc.merge.rdx");
+    ResumePhiR->setOperand(0, ResumeFromVectorLoop);
   }
 }
 

[fhahn]

The initial plan now already has the operands of the scalar header phis set up correctly, so this change is not needed any more to fix them up.

[fhahn]

The initial plan now already has the operands of the scalar header phis set up correctly, so here we now add anothe operand to trigger a mismatch between #incoming values and #predecessors

[fhahn]

ping :)

[fhahn]

Removes one of the few remaining instances that retrieve recipes via IR referneces.