3 files changed, 21 insertions, 2 deletions
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 9d9fe7d376d..0cd24633499 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -3397,8 +3397,14 @@ void Verifier::verifyDominatesUse(Instruction &I, unsigned i) {
       return;
   }
 
+  // Quick check whether the def has already been encountered in the same block.
+  // PHI nodes are not checked to prevent accepting preceeding PHIs, because PHI
+  // uses are defined to happen on the incoming edge, not at the instruction.
+  if (!isa<PHINode>(I) && InstsInThisBlock.count(Op))
+    return;
+
   const Use &U = I.getOperandUse(i);
-  Assert(InstsInThisBlock.count(Op) || DT.dominates(Op, U),
+  Assert(DT.dominates(Op, U),
          "Instruction does not dominate all uses!", Op, &I);
 }
 
diff --git a/llvm/test/Transforms/LoopVectorize/phi-hang.ll b/llvm/test/Transforms/LoopVectorize/phi-hang.ll
index bbce239afa7..eb1aaeffde8 100644
--- a/llvm/test/Transforms/LoopVectorize/phi-hang.ll
+++ b/llvm/test/Transforms/LoopVectorize/phi-hang.ll
@@ -18,7 +18,7 @@ bb4:                                              ; preds = %bb3
 
 bb5:                                              ; preds = %bb4, %bb1
   %tmp6 = phi i32 [ 0, %bb4 ], [ %tmp, %bb1 ]
-  %tmp7 = phi i32 [ 0, %bb4 ], [ %tmp6, %bb1 ]
+  %tmp7 = phi i32 [ 0, %bb4 ], [ %tmp, %bb1 ]
   %tmp8 = phi i32 [ 0, %bb4 ], [ %tmp, %bb1 ]
   %tmp9 = add nsw i32 %tmp2, 1
   %tmp10 = icmp eq i32 %tmp9, 0
diff --git a/llvm/test/Verifier/dominates.ll b/llvm/test/Verifier/dominates.ll
index c5424bbede3..6b0c67f7a2b 100644
--- a/llvm/test/Verifier/dominates.ll
+++ b/llvm/test/Verifier/dominates.ll
@@ -55,3 +55,16 @@ bb1:
 ; CHECK-NEXT:  %y1 = add i32 %x, 1
 ; CHECK-NEXT:  %y3 = phi i32 [ %y1, %bb0 ]
 }
+
+define void @f5() {
+entry:
+  br label %next
+
+next:
+  %y = phi i32 [ 0, %entry ]
+  %x = phi i32 [ %y, %entry ]
+  ret void
+; CHECK: Instruction does not dominate all uses!
+; CHECK-NEXT:  %y = phi i32 [ 0, %entry ]
+; CHECK-NEXT:  %x = phi i32 [ %y, %entry ]
+}