Subzero WASM: avoid needless comparisons, add bounds check flag option

src/IceOperand.h

 //===- subzero/src/IceOperand.h - High-level operands -----------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 33 matching lines @@
     kConstInteger32,
     kConstInteger64,
     kConstFloat,
     kConstDouble,
     kConstRelocatable,
     kConstUndef,
     kConst_Target, // leave space for target-specific constant kinds
     kConst_Max = kConst_Target + MaxTargetKinds,
     kVariable,
     kVariable64On32,
+    kVariableBoolean,
     kVariable_Target, // leave space for target-specific variable kinds
     kVariable_Max = kVariable_Target + MaxTargetKinds,
     // Target-specific operand classes use kTarget as the starting point for
     // their Kind enum space. Note that the value-spaces are shared across
     // targets. To avoid confusion over the definition of shared values, an
     // object specific to one target should never be passed to a different
     // target.
     kTarget,
     kTarget_Max = std::numeric_limits<uint8_t>::max(),
   };
@@ skipping 24 matching lines @@
     dump(Func, Func->getContext()->getStrDump());
   }
   void dump(Ostream &Str) const {
     if (BuildDefs::dump())
       dump(nullptr, Str);
   }
   /// @}
 
   virtual ~Operand() = default;
 
+  virtual Variable *asBoolean() { return nullptr; }
+
 protected:
   Operand(OperandKind Kind, Type Ty) : Ty(Ty), Kind(Kind) {
     // It is undefined behavior to have a larger value in the enum
     assert(Kind <= kTarget_Max);
   }
 
   const Type Ty;
   const OperandKind Kind;
   /// Vars and NumVars are initialized by the derived class.
   SizeT NumVars = 0;
@@ skipping 869 matching lines @@
   /// loop nest depth factor for each use.
   RegWeight getUseWeight(const Variable *Var) const;
 
 private:
   const Cfg *Func;
   MetadataKind Kind;
   CfgVector<VariableTracking> Metadata;
   const static InstDefList NoDefinitions;
 };
 
+/// BooleanVariable represents a variable that was the zero-extended result of a
+/// comparison. It maintains a pointer to its original i1 source so that the
+/// WASM frontend can avoid adding needless comparisons.
+class BooleanVariable : public Variable {
+  BooleanVariable() = delete;
+  BooleanVariable(const BooleanVariable &) = delete;
+  BooleanVariable &operator=(const BooleanVariable &) = delete;
+
+  BooleanVariable(const Cfg *Func, OperandKind K, Type Ty, SizeT Index)
+      : Variable(Func, K, Ty, Index) {}
+
+public:
+  static BooleanVariable *create(Cfg *Func, Type Ty, SizeT Index) {
+    return new (Func->allocate<BooleanVariable>())
+        BooleanVariable(Func, kVariable, Ty, Index);
+  }
+
+  virtual Variable *asBoolean() { return BoolSource; }
+
+  void setBoolSource(Variable *Src) { BoolSource = Src; }
+
+  static bool classof(const Operand *Operand) {
+    return Operand->getKind() == kVariableBoolean;
+  }
+
+private:
+  Variable *BoolSource = nullptr;
+};
+
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEOPERAND_H