Subzero: Allow delaying Phi lowering until after register allocation.

src/IceInst.h

Index: src/IceInst.h
diff --git a/src/IceInst.h b/src/IceInst.h
index 0a47e1a50821880994e1c52fc139221abc612973..aba4ce02b44cb04de1a18f6f3baa5e0df921ce05 100644
--- a/src/IceInst.h
+++ b/src/IceInst.h
@@ -100,11 +100,21 @@ public:
         "getTerminatorEdges() called on a non-terminator instruction");
     return NodeList();
   }
+  virtual bool isUnconditionalBranch() const { return false; }
+  // If the instruction is a branch-type instruction with OldNode as a
+  // target, repoint it to NewNode and return true, otherwise return
+  // false.  Only repoint one instance, even if the instruction has
+  // multiple instances of OldNode as a target.
+  virtual bool repointEdge(CfgNode *OldNode, CfgNode *NewNode) {
+    (void)OldNode;
+    (void)NewNode;
+    return false;
+  }
 
   virtual bool isSimpleAssign() const { return false; }
 
   void livenessLightweight(Cfg *Func, LivenessBV &Live);
-  void liveness(InstNumberT InstNumber, LivenessBV &Live, Liveness *Liveness,
+  bool liveness(InstNumberT InstNumber, LivenessBV &Live, Liveness *Liveness,

[jvoung (off chromium), 2014/10/27 22:12:21]

document the meaning of the "bool" return value of liveness()?

[Jim Stichnoth, 2014/10/28 01:20:14]

I had documented it in the .cpp file, so I moved that comment over here.

(It looks like I am very inconsistent about .h versus .cpp documentation, so
that should be fixed at some point.)

                 LiveBeginEndMap *LiveBegin, LiveBeginEndMap *LiveEnd);
 
   // Get the number of native instructions that this instruction
@@ -304,6 +314,8 @@ public:
     return getTargetFalse();
   }
   NodeList getTerminatorEdges() const override;
+  bool isUnconditionalBranch() const override { return isUnconditional(); }
+  bool repointEdge(CfgNode *OldNode, CfgNode *NewNode) override;
   void dump(const Cfg *Func) const override;
   static bool classof(const Inst *Inst) { return Inst->getKind() == Br; }
 
@@ -314,8 +326,8 @@ private:
   InstBr(Cfg *Func, CfgNode *Target);
   ~InstBr() override {}
 
-  CfgNode *const TargetFalse; // Doubles as unconditional branch target
-  CfgNode *const TargetTrue;  // NULL if unconditional branch
+  CfgNode *TargetFalse; // Doubles as unconditional branch target
+  CfgNode *TargetTrue;  // NULL if unconditional branch
 };
 
 // Call instruction.  The call target is captured as getSrc(0), and
@@ -671,6 +683,7 @@ public:
   }
   void addBranch(SizeT CaseIndex, uint64_t Value, CfgNode *Label);
   NodeList getTerminatorEdges() const override;
+  bool repointEdge(CfgNode *OldNode, CfgNode *NewNode) override;
   void dump(const Cfg *Func) const override;
   static bool classof(const Inst *Inst) { return Inst->getKind() == Switch; }