diff --git a/lib/Transforms/Scalar/Reassociate.cpp b/lib/Transforms/Scalar/Reassociate.cpp
index b572f4eb077..69cdc0f7991 100644
--- a/lib/Transforms/Scalar/Reassociate.cpp
+++ b/lib/Transforms/Scalar/Reassociate.cpp
@@ -673,16 +673,10 @@ void Reassociate::RewriteExprTree(BinaryOperator *I,
   // original in some non-trivial way, requiring the clearing of optional flags.
   // Flags are cleared from the operator in ExpressionChanged up to I inclusive.
   BinaryOperator *ExpressionChanged = 0;
-  BinaryOperator *Previous;
-  BinaryOperator *Op = 0;
-  for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
+  for (unsigned i = 0; ; ++i) {
     assert(!NodesToRewrite.empty() &&
            "Optimized expressions has more nodes than original!");
-    Previous = Op; Op = NodesToRewrite.pop_back_val();
-    if (ExpressionChanged)
-      // Compactify the tree instructions together with each other to guarantee
-      // that the expression tree is dominated by all of Ops.
-      Op->moveBefore(Previous);
+    BinaryOperator *Op = NodesToRewrite.pop_back_val();
 
     // The last operation (which comes earliest in the IR) is special as both
     // operands will come from Ops, rather than just one with the other being
@@ -771,15 +765,17 @@ void Reassociate::RewriteExprTree(BinaryOperator *I,
   }
 
   // If the expression changed non-trivially then clear out all subclass data
-  // starting from the operator specified in ExpressionChanged.
-  if (ExpressionChanged) {
+  // starting from the operator specified in ExpressionChanged, and compactify
+  // the operators to just before the expression root to guarantee that the
+  // expression tree is dominated by all of Ops.
+  if (ExpressionChanged)
     do {
       ExpressionChanged->clearSubclassOptionalData();
       if (ExpressionChanged == I)
         break;
+      ExpressionChanged->moveBefore(I);
       ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->use_begin());
     } while (1);
-  }
 
   // Throw away any left over nodes from the original expression.
   for (unsigned i = 0, e = NodesToRewrite.size(); i != e; ++i)
diff --git a/test/Transforms/Reassociate/crash.ll b/test/Transforms/Reassociate/crash.ll
index e2ebcddf6b1..a99c844f01a 100644
--- a/test/Transforms/Reassociate/crash.ll
+++ b/test/Transforms/Reassociate/crash.ll
@@ -119,3 +119,17 @@ for.cond:                                         ; preds = %for.cond, %entry
   %conv = zext i16 %p to i32
   br label %for.cond
 }
+
+; PR12963
+@a = external global i8
+define i8 @f0(i8 %x) {
+  %t0 = load i8* @a
+  %t1 = mul i8 %x, %x
+  %t2 = mul i8 %t1, %t1
+  %t3 = mul i8 %t2, %t2
+  %t4 = mul i8 %t3, %x
+  %t5 = mul i8 %t4, %t4
+  %t6 = mul i8 %t5, %x
+  %t7 = mul i8 %t6, %t0
+  ret i8 %t7
+}