[SubZero] Branch optimization

src/IceInstMIPS32.h

 //===- subzero/src/IceInstMIPS32.h - MIPS32 machine instrs --*- C++ -*-===    //
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 183 matching lines @@
     Trunc_l_d,
     Trunc_l_s,
     Trunc_w_d,
     Trunc_w_s,
     Xor,
     Xori
   };
 
   static const char *getWidthString(Type Ty);
 
+  CondMIPS32::Cond getOppositeCondition(CondMIPS32::Cond Cond);
+
   void dump(const Cfg *Func) const override;
 
   void dumpOpcode(Ostream &Str, const char *Opcode, Type Ty) const {
     Str << Opcode << "." << Ty;
   }
 
   // TODO(rkotler): while branching is not implemented
   bool repointEdges(CfgNode *, CfgNode *) override { return true; }
 
   /// Shared emit routines for common forms of instructions.
@@ skipping 448 matching lines @@
   static InstMIPS32Br *create(Cfg *Func, CfgNode *TargetTrue,
                               CfgNode *TargetFalse, Operand *Src0,
                               CondMIPS32::Cond Cond) {
     constexpr InstMIPS32Label *NoLabel = nullptr;
     return new (Func->allocate<InstMIPS32Br>())
         InstMIPS32Br(Func, TargetTrue, TargetFalse, Src0, NoLabel, Cond);
   }
 
   const CfgNode *getTargetTrue() const { return TargetTrue; }
   const CfgNode *getTargetFalse() const { return TargetFalse; }
-
+  CondMIPS32::Cond getPredicate() const { return Predicate; }
+  void setPredicate(CondMIPS32::Cond Pred) { Predicate = Pred; }
+  bool optimizeBranch(const CfgNode *NextNode);
   bool isUnconditionalBranch() const override {
     return Predicate == CondMIPS32::AL;
   }
   bool repointEdges(CfgNode *OldNode, CfgNode *NewNode) override;
   void emit(const Cfg *Func) const override;
   void emitIAS(const Cfg *Func) const override { (void)Func; };
   void dump(const Cfg *Func) const override;
   static bool classof(const Inst *Instr) { return isClassof(Instr, Br); }
 
 private:
   InstMIPS32Br(Cfg *Func, const CfgNode *TargetTrue, const CfgNode *TargetFalse,
                const InstMIPS32Label *Label, const CondMIPS32::Cond Cond);
 
   InstMIPS32Br(Cfg *Func, const CfgNode *TargetTrue, const CfgNode *TargetFalse,
                Operand *Src0, const InstMIPS32Label *Label,
                const CondMIPS32::Cond Cond);
 
   InstMIPS32Br(Cfg *Func, const CfgNode *TargetTrue, const CfgNode *TargetFalse,
                Operand *Src0, Operand *Src1, const InstMIPS32Label *Label,
                const CondMIPS32::Cond Cond);
 
   const CfgNode *TargetTrue;
   const CfgNode *TargetFalse;
   const InstMIPS32Label *Label; // Intra-block branch target
-  const CondMIPS32::Cond Predicate;
+  CondMIPS32::Cond Predicate;
 };
 
 class InstMIPS32Call : public InstMIPS32 {
   InstMIPS32Call() = delete;
   InstMIPS32Call(const InstMIPS32Call &) = delete;
   InstMIPS32Call &operator=(const InstMIPS32Call &) = delete;
 
 public:
   static InstMIPS32Call *create(Cfg *Func, Variable *Dest,
                                 Operand *CallTarget) {
@@ skipping 192 matching lines @@
 template <> void InstMIPS32Mtlo::emit(const Cfg *Func) const;
 template <> void InstMIPS32Mthi::emit(const Cfg *Func) const;
 template <> void InstMIPS32Mult::emit(const Cfg *Func) const;
 template <> void InstMIPS32Multu::emit(const Cfg *Func) const;
 template <> void InstMIPS32Lui::emit(const Cfg *Func) const;
 
 } // end of namespace MIPS32
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEINSTMIPS32_H