Index: llvm/trunk/include/llvm/Transforms/Scalar/GVN.h
===================================================================
--- llvm/trunk/include/llvm/Transforms/Scalar/GVN.h
+++ llvm/trunk/include/llvm/Transforms/Scalar/GVN.h
@@ -111,6 +111,7 @@
                             Value *LHS, Value *RHS);
     uint32_t phiTranslate(const BasicBlock *BB, const BasicBlock *PhiBlock,
                           uint32_t Num, GVN &Gvn);
+    void eraseTranslateCacheEntry(uint32_t Num, const BasicBlock &CurrBlock);
     bool exists(Value *V) const;
     void add(Value *V, uint32_t num);
     void clear();
Index: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp
@@ -1558,6 +1558,17 @@
   return Num;
 }
 
+/// Erase stale entry from phiTranslate cache so phiTranslate can be computed
+/// again.
+void GVN::ValueTable::eraseTranslateCacheEntry(uint32_t Num,
+                                               const BasicBlock &CurrBlock) {
+  for (const BasicBlock *Pred : predecessors(&CurrBlock)) {
+    auto FindRes = PhiTranslateTable.find({Num, Pred});
+    if (FindRes != PhiTranslateTable.end())
+      PhiTranslateTable.erase(FindRes);
+  }
+}
+
 // In order to find a leader for a given value number at a
 // specific basic block, we first obtain the list of all Values for that number,
 // and then scan the list to find one whose block dominates the block in
@@ -2210,6 +2221,9 @@
   }
 
   VN.add(Phi, ValNo);
+  // After creating a new PHI for ValNo, the phi translate result for ValNo will
+  // be changed, so erase the related stale entries in phi translate cache.
+  VN.eraseTranslateCacheEntry(ValNo, *CurrentBlock);
   addToLeaderTable(ValNo, Phi, CurrentBlock);
   Phi->setDebugLoc(CurInst->getDebugLoc());
   CurInst->replaceAllUsesWith(Phi);
Index: llvm/trunk/test/Transforms/GVN/PRE/phi-translate-2.ll
===================================================================
--- llvm/trunk/test/Transforms/GVN/PRE/phi-translate-2.ll
+++ llvm/trunk/test/Transforms/GVN/PRE/phi-translate-2.ll
@@ -129,3 +129,48 @@
 critedge.loopexit:
   unreachable
 }
+
+; Check sub expression will be pre transformed.
+; CHECK-LABEL: @test5(
+; CHECK: entry:
+; CHECK: %sub.ptr.sub = sub i64 %sub.ptr.lhs.cast, %sub.ptr.rhs.cast
+; CHECK: br i1 %cmp
+; CHECK: if.then2:
+; CHECK: %[[PTRTOINT:.*]] = ptrtoint i32* %add.ptr to i64
+; CHECK: %[[SUB:.*]] = sub i64 %sub.ptr.lhs.cast, %[[PTRTOINT]]
+; CHECK: br label %if.end3
+; CHECK: if.end3:
+; CHECK: %[[PREPHI:.*]] = phi i64 [ %sub.ptr.sub, %if.else ], [ %[[SUB]], %if.then2 ], [ %sub.ptr.sub, %entry ]
+; CHECK: %[[DIV:.*]] = ashr exact i64 %[[PREPHI]], 2
+; CHECK: ret i64 %[[DIV]]
+
+declare void @bar(...) local_unnamed_addr #1
+
+; Function Attrs: nounwind uwtable
+define i64 @test5(i32* %start, i32* %e, i32 %n1, i32 %n2) local_unnamed_addr #0 {
+entry:
+  %sub.ptr.lhs.cast = ptrtoint i32* %e to i64
+  %sub.ptr.rhs.cast = ptrtoint i32* %start to i64
+  %sub.ptr.sub = sub i64 %sub.ptr.lhs.cast, %sub.ptr.rhs.cast
+  %cmp = icmp sgt i64 %sub.ptr.sub, 4000
+  br i1 %cmp, label %if.then, label %if.end3
+
+if.then:                                          ; preds = %entry
+  %cmp1 = icmp sgt i32 %n1, %n2
+  br i1 %cmp1, label %if.then2, label %if.else
+
+if.then2:                                         ; preds = %if.then
+  %add.ptr = getelementptr inbounds i32, i32* %start, i64 800
+  br label %if.end3
+
+if.else:                                          ; preds = %if.then
+  tail call void (...) @bar() #2
+  br label %if.end3
+
+if.end3:                                          ; preds = %if.then2, %if.else, %entry
+  %p.0 = phi i32* [ %add.ptr, %if.then2 ], [ %start, %if.else ], [ %start, %entry ]
+  %sub.ptr.rhs.cast5 = ptrtoint i32* %p.0 to i64
+  %sub.ptr.sub6 = sub i64 %sub.ptr.lhs.cast, %sub.ptr.rhs.cast5
+  %sub.ptr.div7 = ashr exact i64 %sub.ptr.sub6, 2
+  ret i64 %sub.ptr.div7
+}