Subzero: Allow delaying Phi lowering until after register allocation.

src/IceInstX8632.h

Index: src/IceInstX8632.h
diff --git a/src/IceInstX8632.h b/src/IceInstX8632.h
index 177843705355b9660a574fb233a0255d22929705..f9761051a63db5a870610526493b4e91051434a5 100644
--- a/src/IceInstX8632.h
+++ b/src/IceInstX8632.h
@@ -387,6 +387,10 @@ public:
       ++Sum;
     return Sum;
   }
+  bool isUnconditionalBranch() const override {
+    return !Label && Condition == CondX86::Br_None;
+  }
+  bool repointEdge(CfgNode *OldNode, CfgNode *NewNode) override;
   void emit(const Cfg *Func) const override;
   void emitIAS(const Cfg *Func) const override;
   void dump(const Cfg *Func) const override;