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

src/IceOperand.h

Index: src/IceOperand.h
diff --git a/src/IceOperand.h b/src/IceOperand.h
index 26630dfb7584c929b10730a5cd9d5545c04a411f..b3e0f5f027a8a80c8a84f094d4a2d20f4b98d3df 100644
--- a/src/IceOperand.h
+++ b/src/IceOperand.h
@@ -51,6 +51,7 @@ public:
     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
@@ -95,6 +96,8 @@ public:
 
   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
@@ -984,6 +987,35 @@ private:
   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