Index: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp
@@ -2288,9 +2288,12 @@
       PHINode::Create(CurInst->getType(), predMap.size(),
                       CurInst->getName() + ".pre-phi", &CurrentBlock->front());
   for (unsigned i = 0, e = predMap.size(); i != e; ++i) {
-    if (Value *V = predMap[i].first)
+    if (Value *V = predMap[i].first) {
+      // If we use an existing value in this phi, we have to patch the original
+      // value because the phi will be used to replace a later value.
+      patchReplacementInstruction(CurInst, V);
       Phi->addIncoming(V, predMap[i].second);
-    else
+    } else
       Phi->addIncoming(PREInstr, PREPred);
   }
 
Index: llvm/trunk/test/Transforms/GVN/PRE/pre-jt-add.ll
===================================================================
--- llvm/trunk/test/Transforms/GVN/PRE/pre-jt-add.ll
+++ llvm/trunk/test/Transforms/GVN/PRE/pre-jt-add.ll
@@ -0,0 +1,36 @@
+; RUN: opt < %s -gvn -enable-pre -jump-threading -S | FileCheck %s
+
+@H = common global i32 0
+@G = common global i32 0
+
+define i32 @test(i1 %cond, i32 %v) nounwind {
+; CHECK-LABEL: @test
+entry:
+  br i1 %cond, label %bb, label %bb1
+
+bb:
+; CHECK: store
+; CHECK-NOT: br label %return
+  %add.1 = add nuw nsw i32 %v, -1
+  store i32 %add.1, i32* @G, align 4
+  br label %merge
+
+bb1:
+  br label %merge
+
+merge:
+  %add.2 = add i32 %v, -1
+  %cmp = icmp sgt i32 %add.2, 0
+  br i1 %cmp, label %action, label %return
+
+action:
+; CHECK: store
+; CHECK-NEXT: br label %return
+  store i32 %add.2, i32* @H, align 4
+  br label %return
+
+return:
+  %p = phi i32 [0, %merge], [1, %action]
+  ret i32 %p
+}
+
Index: llvm/trunk/test/Transforms/GVN/PRE/pre-poison-add.ll
===================================================================
--- llvm/trunk/test/Transforms/GVN/PRE/pre-poison-add.ll
+++ llvm/trunk/test/Transforms/GVN/PRE/pre-poison-add.ll
@@ -0,0 +1,52 @@
+; RUN: opt < %s -gvn -enable-pre -S | FileCheck %s
+
+@H = common global i32 0
+@G = common global i32 0
+
+define i32 @test1(i1 %cond, i32 %v) nounwind {
+; CHECK-LABEL: @test1
+entry:
+    br i1 %cond, label %bb, label %bb1
+
+bb:
+    %add.1 = add nuw nsw i32 %v, 42
+; CHECK: %add.1 = add i32 %v, 42
+    store i32 %add.1, i32* @G, align 4
+    br label %return
+
+bb1:
+; CHECK: %.pre = add i32 %v, 42
+    br label %return
+
+return:
+; CHECK: %add.2.pre-phi = phi i32 [ %.pre, %bb1 ], [ %add.1, %bb ]
+; CHECK-NEXT: store i32 %add.2.pre-phi, i32* @H, align 4
+; CHECK-NEXT: ret i32 0
+    %add.2 = add i32 %v, 42
+    store i32 %add.2, i32* @H, align 4
+    ret i32 0
+}
+
+define i32 @test2(i1 %cond, i32 %v) nounwind {
+; CHECK-LABEL: @test2
+entry:
+    br i1 %cond, label %bb, label %bb1
+
+bb:
+    %add.1 = add i32 %v, 42
+; CHECK: %add.1 = add i32 %v, 42
+    store i32 %add.1, i32* @G, align 4
+    br label %return
+
+bb1:
+; CHECK: %.pre = add nuw nsw i32 %v, 42
+    br label %return
+
+return:
+; CHECK: %add.2.pre-phi = phi i32 [ %.pre, %bb1 ], [ %add.1, %bb ]
+; CHECK-NEXT: store i32 %add.2.pre-phi, i32* @H, align 4
+; CHECK-NEXT: ret i32 0
+    %add.2 = add nuw nsw i32 %v, 42
+    store i32 %add.2, i32* @H, align 4
+    ret i32 0
+}