!fxup improve verifier message, add verification test.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlanVerifier.cpp

@@ -219,15 +219,22 @@ bool VPlanVerifier::verifyVPBasicBlock(const VPBasicBlock *VPBB) {
 
       for (const VPUser *U : V->users()) {
         auto *UI = cast<VPRecipeBase>(U);
-        const VPBlockBase *UserVPBB = UI->getParent();
         if (auto *Phi = dyn_cast<VPPhiAccessors>(UI)) {
           for (unsigned Idx = 0; Idx != Phi->getNumIncoming(); ++Idx) {
             VPValue *IncVPV = Phi->getIncomingValue(Idx);
             const VPBasicBlock *IncVPBB = Phi->getIncomingBlock(Idx);
             if (IncVPV != V)
               continue;
             if (IncVPBB != VPBB && !VPDT.dominates(VPBB, IncVPBB)) {
-              errs() << "Use before def!\n";
+              errs() << "Incoming def at index " << Idx
+                     << " does not dominate incoming block!\n";
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+              VPSlotTracker Tracker(VPBB->getPlan());
+              IncVPV->getDefiningRecipe()->print(errs(), "  ", Tracker);
+              errs() << "\n  does not dominate " << IncVPBB->getName()
+                     << " for\n";
+              UI->print(errs(), "  ", Tracker);
+#endif
               return false;
             }
           }

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));