[VPlan] Verify dominance for incoming values of phi-like recipes. (#124838)

Update the verifier to verify dominance for incoming values for phi-like
recipes. The defining recipe must dominate the incoming block for the
incoming value.

Builds on top of #138472 to
retrieve incoming values & corresponding blocks for phi-like recipes.

PR: #124838

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -1135,7 +1135,9 @@ class VPPhiAccessors {
   const VPBasicBlock *getIncomingBlock(unsigned Idx) const;
 
   /// Returns the number of incoming values, also number of incoming blocks.
-  unsigned getNumIncoming() const { return getAsRecipe()->getNumOperands(); }
+  virtual unsigned getNumIncoming() const {
+    return getAsRecipe()->getNumOperands();
+  }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
   /// Print the recipe.
@@ -1234,7 +1236,7 @@ class VPIRInstruction : public VPRecipeBase {
 /// cast/dyn_cast/isa and execute() implementation. A single VPValue operand is
 /// allowed, and it is used to add a new incoming value for the single
 /// predecessor VPBB.
-struct VPIRPhi : public VPIRInstruction {
+struct VPIRPhi : public VPIRInstruction, public VPPhiAccessors {
   VPIRPhi(PHINode &PN) : VPIRInstruction(PN) {}
 
   static inline bool classof(const VPRecipeBase *U) {
@@ -1251,6 +1253,9 @@ struct VPIRPhi : public VPIRInstruction {
   void print(raw_ostream &O, const Twine &Indent,
              VPSlotTracker &SlotTracker) const override;
 #endif
+
+protected:
+  const VPRecipeBase *getAsRecipe() const override { return this; }
 };
 
 /// Helper to manage IR metadata for recipes. It filters out metadata that
@@ -1785,13 +1790,15 @@ class VPVectorPointerRecipe : public VPRecipeWithIRFlags,
 ///  * VPWidenPointerInductionRecipe: Generate vector and scalar values for a
 ///    pointer induction. Produces either a vector PHI per-part or scalar values
 ///    per-lane based on the canonical induction.
-class VPHeaderPHIRecipe : public VPSingleDefRecipe {
+class VPHeaderPHIRecipe : public VPSingleDefRecipe, public VPPhiAccessors {
 protected:
   VPHeaderPHIRecipe(unsigned char VPDefID, Instruction *UnderlyingInstr,
                     VPValue *Start, DebugLoc DL = {})
       : VPSingleDefRecipe(VPDefID, ArrayRef<VPValue *>({Start}), UnderlyingInstr, DL) {
   }
 
+  const VPRecipeBase *getAsRecipe() const override { return this; }
+
 public:
   ~VPHeaderPHIRecipe() override = default;
 
@@ -1980,6 +1987,11 @@ class VPWidenIntOrFpInductionRecipe : public VPWidenInductionRecipe {
     return isUnrolled() ? getOperand(getNumOperands() - 2) : nullptr;
   }
 
+  /// Returns the number of incoming values, also number of incoming blocks.
+  /// Note that at the moment, VPWidenIntOrFpInductionRecipes only have a single
+  /// incoming value, its start value.
+  unsigned getNumIncoming() const override { return 1; }
+
   /// Returns the first defined value as TruncInst, if it is one or nullptr
   /// otherwise.
   TruncInst *getTruncInst() { return Trunc; }
@@ -3283,6 +3295,46 @@ class VPScalarIVStepsRecipe : public VPRecipeWithIRFlags,
   }
 };
 
+/// Casting from VPRecipeBase -> VPPhiAccessors is supported for all recipe
+/// types implementing VPPhiAccessors. Used by isa<> & co.
+template <> struct CastIsPossible<VPPhiAccessors, const VPRecipeBase *> {
+  static inline bool isPossible(const VPRecipeBase *f) {
+    // TODO: include VPPredInstPHIRecipe too, once it implements VPPhiAccessors.
+    return isa<VPIRPhi, VPHeaderPHIRecipe, VPWidenPHIRecipe, VPPhi>(f);
+  }
+};
+/// Support casting from VPRecipeBase -> VPPhiAccessors, by down-casting to the
+/// recipe types implementing VPPhiAccessors. Used by cast<>, dyn_cast<> & co.
+template <>
+struct CastInfo<VPPhiAccessors, const VPRecipeBase *>
+    : public CastIsPossible<VPPhiAccessors, const VPRecipeBase *> {
+
+  using Self = CastInfo<VPPhiAccessors, const VPRecipeBase *>;
+
+  /// doCast is used by cast<>.
+  static inline VPPhiAccessors *doCast(const VPRecipeBase *R) {
+    return const_cast<VPPhiAccessors *>([R]() -> const VPPhiAccessors * {
+      switch (R->getVPDefID()) {
+      case VPDef::VPInstructionSC:
+        return cast<VPPhi>(R);
+      case VPDef::VPIRInstructionSC:
+        return cast<VPIRPhi>(R);
+      case VPDef::VPWidenPHISC:
+        return cast<VPWidenPHIRecipe>(R);
+      default:
+        return cast<VPHeaderPHIRecipe>(R);
+      }
+    }());
+  }
+
+  /// doCastIfPossible is used by dyn_cast<>.
+  static inline VPPhiAccessors *doCastIfPossible(const VPRecipeBase *f) {
+    if (!Self::isPossible(f))
+      return nullptr;
+    return doCast(f);
+  }
+};
+
 /// VPBasicBlock serves as the leaf of the Hierarchical Control-Flow Graph. It
 /// holds a sequence of zero or more VPRecipe's each representing a sequence of
 /// output IR instructions. All PHI-like recipes must come before any non-PHI recipes.

llvm/lib/Transforms/Vectorize/VPlanVerifier.cpp

@@ -192,8 +192,7 @@ bool VPlanVerifier::verifyVPBasicBlock(const VPBasicBlock *VPBB) {
   if (!verifyPhiRecipes(VPBB))
     return false;
 
-  // Verify that defs in VPBB dominate all their uses. The current
-  // implementation is still incomplete.
+  // Verify that defs in VPBB dominate all their uses.
   DenseMap<const VPRecipeBase *, unsigned> RecipeNumbering;
   unsigned Cnt = 0;
   for (const VPRecipeBase &R : *VPBB)
@@ -220,12 +219,31 @@ bool VPlanVerifier::verifyVPBasicBlock(const VPBasicBlock *VPBB) {
 
       for (const VPUser *U : V->users()) {
         auto *UI = cast<VPRecipeBase>(U);
-        // TODO: check dominance of incoming values for phis properly.
-        if (!UI ||
-            isa<VPHeaderPHIRecipe, VPWidenPHIRecipe, VPPredInstPHIRecipe,
-                VPIRPhi>(UI) ||
-            (isa<VPInstruction>(UI) &&
-             cast<VPInstruction>(UI)->getOpcode() == Instruction::PHI))
+        if (auto *Phi = dyn_cast<VPPhiAccessors>(UI)) {
+          for (unsigned Idx = 0; Idx != Phi->getNumIncoming(); ++Idx) {
+            VPValue *IncomingVPV = Phi->getIncomingValue(Idx);
+            if (IncomingVPV != V)
+              continue;
+
+            const VPBasicBlock *IncomingVPBB = Phi->getIncomingBlock(Idx);
+            if (VPDT.dominates(VPBB, IncomingVPBB))
+              continue;
+
+            errs() << "Incoming def at index " << Idx
+                   << " does not dominate incoming block!\n";
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+            VPSlotTracker Tracker(VPBB->getPlan());
+            IncomingVPV->getDefiningRecipe()->print(errs(), "  ", Tracker);
+            errs() << "\n  does not dominate " << IncomingVPBB->getName()
+                   << " for\n";
+            UI->print(errs(), "  ", Tracker);
+#endif
+            return false;
+          }
+          continue;
+        }
+        // TODO: Also verify VPPredInstPHIRecipe.
+        if (isa<VPPredInstPHIRecipe>(UI))
           continue;
 
         // If the user is in the same block, check it comes after R in the

llvm/unittests/Transforms/Vectorize/VPlanVerifierTest.cpp

@@ -143,6 +143,43 @@ TEST_F(VPVerifierTest, VPBlendUseBeforeDefDifferentBB) {
   delete Phi;
 }
 
+TEST_F(VPVerifierTest, VPPhiIncomingValueDoesntDominateIncomingBlock) {
+  VPlan &Plan = getPlan();
+  IntegerType *Int32 = IntegerType::get(C, 32);
+  VPValue *Zero = Plan.getOrAddLiveIn(ConstantInt::get(Int32, 0));
+
+  VPBasicBlock *VPBB1 = Plan.getEntry();
+  VPBasicBlock *VPBB2 = Plan.createVPBasicBlock("");
+  VPBasicBlock *VPBB3 = Plan.createVPBasicBlock("");
+
+  VPInstruction *DefI = new VPInstruction(Instruction::Add, {Zero});
+  VPPhi *Phi = new VPPhi({DefI}, {});
+  VPBB2->appendRecipe(Phi);
+  VPBB2->appendRecipe(DefI);
+  auto *CanIV = new VPCanonicalIVPHIRecipe(Zero, {});
+  VPBB3->appendRecipe(CanIV);
+
+  VPRegionBlock *R1 = Plan.createVPRegionBlock(VPBB3, VPBB3, "R1");
+  VPBlockUtils::connectBlocks(VPBB1, VPBB2);
+  VPBlockUtils::connectBlocks(VPBB2, R1);
+#if GTEST_HAS_STREAM_REDIRECTION
+  ::testing::internal::CaptureStderr();
+#endif
+  EXPECT_FALSE(verifyVPlanIsValid(Plan));
+#if GTEST_HAS_STREAM_REDIRECTION
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  EXPECT_STREQ("Incoming def at index 0 does not dominate incoming block!\n"
+               "  EMIT vp<%2> = add ir<0>\n"
+               "  does not dominate preheader for\n"
+               "  EMIT vp<%1> = phi [ vp<%2>, preheader ]",
+               ::testing::internal::GetCapturedStderr().c_str());
+#else
+  EXPECT_STREQ("Use before def!\n",
+               ::testing::internal::GetCapturedStderr().c_str());
+#endif
+#endif
+}
+
 TEST_F(VPVerifierTest, DuplicateSuccessorsOutsideRegion) {
   VPlan &Plan = getPlan();
   VPValue *Zero = Plan.getOrAddLiveIn(ConstantInt::get(Type::getInt32Ty(C), 0));