Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -461,6 +461,12 @@
     Value *V = PI == LHS ?
       SimplifyBinOp(Opcode, Incoming, RHS, Q, MaxRecurse) :
       SimplifyBinOp(Opcode, LHS, Incoming, Q, MaxRecurse);
+    // If the simplified operation is equal to the original operation on the
+    // PHI node, it can likewise be safely skipped.
+    if (BinaryOperator *Op = dyn_cast_or_null<BinaryOperator>(V))
+      if (Op->getOpcode() == Opcode &&
+          Op->getOperand(0) == LHS && Op->getOperand(1) == RHS)
+      continue;
     // If the operation failed to simplify, or simplified to a different value
     // to previously, then give up.
     if (!V || (CommonValue && V != CommonValue))
Index: test/Transforms/InstSimplify/phi.ll
===================================================================
--- test/Transforms/InstSimplify/phi.ll
+++ test/Transforms/InstSimplify/phi.ll
@@ -22,3 +22,25 @@
   %e = icmp eq i32 %d, 0
   ret i1 %e
 }
+
+define i32 @test2(i1 %c1, i1 %c2, i32 %x) {
+; CHECK-LABEL: @test2
+; CHECK-NEXT:    [[Y:%.*]] = and i32 %x, -256
+; CHECK:    ret i32 [[Y]]
+;
+  %y = and i32 %x, -256
+  br i1 %c1, label %true, label %false
+true:
+  %a = or i32 %y, 1
+  br label %loop
+false:
+  %b = or i32 %y, 2
+  br label %loop
+loop:
+  %p = phi i32 [ %a, %true ], [ %b, %false ], [ %r, %loop ]
+  %r = and i32 %p, -256
+  br i1 %c2, label %ret, label %loop
+ret:
+  ret i32 %r
+}
+