[llvm] [LV] Allow VPWidenPHI in non-native path and copy DebugLoc (PR #118662)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-vectorizers

Author: Luke Lau (lukel97)

<details>
<summary>Changes</summary>

We can reuse VPWidenPHI in #<!-- -->118638, but it requires us to allow it in the non-native path. We also need to propagate the DebugLoc and use a different name in the generated PHI, so this splits these parts off in case we want it.

We lose some debug info in dbg-outer-loop-vect.ll, but I think this is because the underlying phi node didn't have a DebugLoc to begin with. I think the current version is just carrying over the DebugLoc from the previous state.


---
Full diff: https://github.com/llvm/llvm-project/pull/118662.diff


4 Files Affected:

- (modified) llvm/lib/Transforms/Vectorize/LoopVectorize.cpp (+4-5) 
- (modified) llvm/lib/Transforms/Vectorize/VPlan.h (+8-2) 
- (modified) llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp (+2-4) 
- (modified) llvm/test/Transforms/LoopVectorize/dbg-outer-loop-vect.ll (+2-2) 


``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 3c7c044a042719..33d50de947aa61 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -511,7 +511,7 @@ class InnerLoopVectorizer {
                             VPTransformState &State);
 
   /// Fix the non-induction PHIs in \p Plan.
-  void fixNonInductionPHIs(VPTransformState &State);
+  void fixWidenedPHIs(VPTransformState &State);
 
   /// Create a new phi node for the induction variable \p OrigPhi to resume
   /// iteration count in the scalar epilogue, from where the vectorized loop
@@ -2931,9 +2931,8 @@ LoopVectorizationCostModel::getVectorIntrinsicCost(CallInst *CI,
 }
 
 void InnerLoopVectorizer::fixVectorizedLoop(VPTransformState &State) {
-  // Fix widened non-induction PHIs by setting up the PHI operands.
-  if (EnableVPlanNativePath)
-    fixNonInductionPHIs(State);
+  // Fix widened PHIs by setting up the PHI operands.
+  fixWidenedPHIs(State);
 
   // Forget the original basic block.
   PSE.getSE()->forgetLoop(OrigLoop);
@@ -3070,7 +3069,7 @@ void InnerLoopVectorizer::sinkScalarOperands(Instruction *PredInst) {
   } while (Changed);
 }
 
-void InnerLoopVectorizer::fixNonInductionPHIs(VPTransformState &State) {
+void InnerLoopVectorizer::fixWidenedPHIs(VPTransformState &State) {
   auto Iter = vp_depth_first_deep(Plan.getEntry());
   for (VPBasicBlock *VPBB : VPBlockUtils::blocksOnly<VPBasicBlock>(Iter)) {
     for (VPRecipeBase &P : VPBB->phis()) {
diff --git a/llvm/lib/Transforms/Vectorize/VPlan.h b/llvm/lib/Transforms/Vectorize/VPlan.h
index e1d828f038f9a2..e759cafb391b7c 100644
--- a/llvm/lib/Transforms/Vectorize/VPlan.h
+++ b/llvm/lib/Transforms/Vectorize/VPlan.h
@@ -2285,10 +2285,16 @@ class VPWidenPHIRecipe : public VPSingleDefRecipe {
   /// List of incoming blocks. Only used in the VPlan native path.
   SmallVector<VPBasicBlock *, 2> IncomingBlocks;
 
+  /// Name to use for the generated IR instruction for the widened IV.
+  std::string Name;
+
 public:
   /// Create a new VPWidenPHIRecipe for \p Phi with start value \p Start.
-  VPWidenPHIRecipe(PHINode *Phi, VPValue *Start = nullptr)
-      : VPSingleDefRecipe(VPDef::VPWidenPHISC, ArrayRef<VPValue *>(), Phi) {
+  VPWidenPHIRecipe(PHINode *Phi, VPValue *Start = nullptr,
+                   const Twine &Name = "vec.phi")
+      : VPSingleDefRecipe(VPDef::VPWidenPHISC, ArrayRef<VPValue *>(), Phi,
+                          Phi->getDebugLoc()),
+        Name(Name.str()) {
     if (Start)
       addOperand(Start);
   }
diff --git a/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp b/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
index ef5f6e22f82206..829ae7c80e0578 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp
@@ -3417,12 +3417,10 @@ void VPReductionPHIRecipe::print(raw_ostream &O, const Twine &Indent,
 #endif
 
 void VPWidenPHIRecipe::execute(VPTransformState &State) {
-  assert(EnableVPlanNativePath &&
-         "Non-native vplans are not expected to have VPWidenPHIRecipes.");
-
+  State.setDebugLocFrom(getDebugLoc());
   Value *Op0 = State.get(getOperand(0));
   Type *VecTy = Op0->getType();
-  Value *VecPhi = State.Builder.CreatePHI(VecTy, 2, "vec.phi");
+  Value *VecPhi = State.Builder.CreatePHI(VecTy, 2, Name);
   State.set(this, VecPhi);
 }
 
diff --git a/llvm/test/Transforms/LoopVectorize/dbg-outer-loop-vect.ll b/llvm/test/Transforms/LoopVectorize/dbg-outer-loop-vect.ll
index 66aceab9fb27c8..44afa34100c299 100644
--- a/llvm/test/Transforms/LoopVectorize/dbg-outer-loop-vect.ll
+++ b/llvm/test/Transforms/LoopVectorize/dbg-outer-loop-vect.ll
@@ -15,8 +15,8 @@ define void @foo(ptr %h) !dbg !4 {
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[FOR_COND_CLEANUP32:%.*]] ]
 ; CHECK-NEXT:    br label [[FOR_COND5_PREHEADER1:%.*]], !dbg [[DBG21]]
 ; CHECK:       for.cond5.preheader1:
-; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x i64> [ zeroinitializer, [[VECTOR_BODY]] ], [ [[TMP4:%.*]], [[FOR_COND5_PREHEADER1]] ], !dbg [[DBG21]]
-; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr i32, ptr [[H]], <4 x i64> [[VEC_PHI]], !dbg [[DBG21]]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <4 x i64> [ zeroinitializer, [[VECTOR_BODY]] ], [ [[TMP4:%.*]], [[FOR_COND5_PREHEADER1]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr i32, ptr [[H]], <4 x i64> [[VEC_PHI]]
 ; CHECK-NEXT:    call void @llvm.masked.scatter.v4i32.v4p0(<4 x i32> zeroinitializer, <4 x ptr> [[TMP0]], i32 4, <4 x i1> splat (i1 true)), !dbg [[DBG22:![0-9]+]]
 ; CHECK-NEXT:    [[TMP1:%.*]] = getelementptr i32, <4 x ptr> [[TMP0]], i64 1, !dbg [[DBG22]]
 ; CHECK-NEXT:    call void @llvm.masked.scatter.v4i32.v4p0(<4 x i32> splat (i32 1), <4 x ptr> [[TMP1]], i32 4, <4 x i1> splat (i1 true)), !dbg [[DBG22]]

``````````

</details>


https://github.com/llvm/llvm-project/pull/118662