C++: add RelationalOpcode and RelationalInstruction

cpp/ql/src/semmle/code/cpp/ir/implementation/Opcode.qll

@@ -76,6 +76,8 @@ abstract class PointerOffsetOpcode extends PointerArithmeticOpcode {}
 
 abstract class CompareOpcode extends BinaryOpcode {}
 
+abstract class RelationalOpcode extends CompareOpcode {}
+
 abstract class CopyOpcode extends Opcode {}
 
 abstract class MemoryAccessOpcode extends Opcode {}
@@ -117,10 +119,10 @@ module Opcode {
   class LogicalNot extends UnaryOpcode, TLogicalNot { override final string toString() { result = "LogicalNot" } }
   class CompareEQ extends CompareOpcode, TCompareEQ { override final string toString() { result = "CompareEQ" } }
   class CompareNE extends CompareOpcode, TCompareNE { override final string toString() { result = "CompareNE" } }
-  class CompareLT extends CompareOpcode, TCompareLT { override final string toString() { result = "CompareLT" } }
-  class CompareGT extends CompareOpcode, TCompareGT { override final string toString() { result = "CompareGT" } }
-  class CompareLE extends CompareOpcode, TCompareLE { override final string toString() { result = "CompareLE" } }
-  class CompareGE extends CompareOpcode, TCompareGE { override final string toString() { result = "CompareGE" } }
+  class CompareLT extends RelationalOpcode, TCompareLT { override final string toString() { result = "CompareLT" } }
+  class CompareGT extends RelationalOpcode, TCompareGT { override final string toString() { result = "CompareGT" } }
+  class CompareLE extends RelationalOpcode, TCompareLE { override final string toString() { result = "CompareLE" } }
+  class CompareGE extends RelationalOpcode, TCompareGE { override final string toString() { result = "CompareGE" } }
   class PointerAdd extends PointerOffsetOpcode, TPointerAdd { override final string toString() { result = "PointerAdd" } }
   class PointerSub extends PointerOffsetOpcode, TPointerSub { override final string toString() { result = "PointerSub" } }
   class PointerDiff extends PointerArithmeticOpcode, TPointerDiff { override final string toString() { result = "PointerDiff" } }

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/Instruction.qll

@@ -967,28 +967,69 @@ class CompareNEInstruction extends CompareInstruction {
   }
 }
 
-class CompareLTInstruction extends CompareInstruction {
+class RelationalInstruction extends CompareInstruction {
+  RelationalInstruction() {
+    opcode instanceof RelationalOpcode
+  }
+
+  abstract Instruction getGreaterOperand();
+  abstract Instruction getLesserOperand();
+}
+
+class CompareLTInstruction extends RelationalInstruction {
   CompareLTInstruction() {
     opcode instanceof Opcode::CompareLT
   }
+
+  override Instruction getLesserOperand() {
+    result = getLeftOperand()
+  }
+
+  override Instruction getGreaterOperand() {
+    result = getRightOperand()
+  }
 }
 
-class CompareGTInstruction extends CompareInstruction {
+class CompareGTInstruction extends RelationalInstruction {
   CompareGTInstruction() {
     opcode instanceof Opcode::CompareGT
   }
-}
 
-class CompareLEInstruction extends CompareInstruction {
-  CompareLEInstruction() {
-    opcode instanceof Opcode::CompareLE
+  override Instruction getLesserOperand() {
+    result = getRightOperand()
+  }
+
+  override Instruction getGreaterOperand() {
+    result = getLeftOperand()
   }
 }
 
-class CompareGEInstruction extends CompareInstruction {
+class CompareLEInstruction extends RelationalInstruction {
+  CompareLEInstruction() {
+    opcode instanceof Opcode::CompareLE
+  }
+
+  override Instruction getLesserOperand() {
+    result = getLeftOperand()
+  }
+
+  override Instruction getGreaterOperand() {
+    result = getRightOperand()
+  }
+}
+
+class CompareGEInstruction extends RelationalInstruction {
   CompareGEInstruction() {
     opcode instanceof Opcode::CompareGE
   }
+
+  override Instruction getLesserOperand() {
+    result = getRightOperand()
+  }
+
+  override Instruction getGreaterOperand() {
+    result = getLeftOperand()
+  }
 }
 
 class SwitchInstruction extends Instruction {