Cache common constants before lowering.

src/IceTargetLoweringX8632.h

Index: src/IceTargetLoweringX8632.h
diff --git a/src/IceTargetLoweringX8632.h b/src/IceTargetLoweringX8632.h
index 8a0db78c49bbb119ee457bca4f1a737d13586c6e..9e27a54e9546877f42665d306f7589200d58706d 100644
--- a/src/IceTargetLoweringX8632.h
+++ b/src/IceTargetLoweringX8632.h
@@ -70,7 +70,7 @@ private:
   explicit TargetX8632(Cfg *Func) : TargetX86Base(Func) {}
 
   Operand *createNaClReadTPSrcOperand() {
-    Constant *Zero = Ctx->getConstantZero(IceType_i32);
+    Constant *Zero = getConstantZero(IceType_i32);
     return Traits::X86OperandMem::create(Func, IceType_i32, nullptr, Zero,
                                          nullptr, 0,
                                          Traits::X86OperandMem::SegReg_GS);