C++: Replace 'Argument -1 indirection' with 'This indirection'

[MathiasVP]

Now that arguments are present in IR path explanations (since #5361), this PR gets rid of the Argument -1 indirection string on indirections for this.

(Part of https://github.com/github/codeql-c-analysis-team/issues/242.)

[jbj]

This indirection is a case of this causing grammatical confusion because this might be mistaken for an English word rather than the this pointer. (sorry)

How about 'this-indirection' or 'this-object' instead? Then it's in lower case, and the hyphen prevents confusion with the English word.

[jbj]

I also liked *this for its brevity, but that style seems to have fallen out of favour after #5361.

[MathiasVP]

This indirection is a case of this causing grammatical confusion because this might be mistaken for an English word rather than the this pointer. (sorry)

How about 'this-indirection' or 'this-object' instead? Then it's in lower case, and the hyphen prevents confusion with the English word.

I like this-indirection. I picked This indirection since it matched with what we have for ArgumentNodes (which are currently shown as This argument). Whatever we end up showing in the path explanations, I think they should follow the same grammatical style.

[MathiasVP]

I also liked *this for its brevity, but that style seems to have fallen out of favour after #5361.

I'm not sure I understand what you mean. The *this string should still be present for the parameter indirection. So after merging this PR (argh, too many this!) and #5361 we should have flow from This indirection to *this in path explanations.

[MathiasVP]

0f6c56a changes the names to better match the AST dataflow library. The number of strings generated appears to be mostly unchanged. On main with Wireshark we get:

Tuple counts for DataFlowUtil::Node::toString_dispred#ff/2@f564a8:
    17746    ~1%     {2} r1 = SCAN DataFlowUtil::ThisParameterNode#class#ff OUTPUT In.0 'this', "this"
    17746    ~1%     {2} r2 = STREAM DEDUP r1
    
    477155   ~0%     {2} r3 = JOIN DataFlowUtil::ParameterNode::isParameterOf_dispred#fff#shared WITH Element::ElementBase::toString_dispred#ff@staged_ext ON FIRST 1 OUTPUT Lhs.1 'this', Rhs.1 'result'
    
    494901   ~2%     {2} r4 = r2 UNION r3
    
    5520951  ~3%     {2} r5 = SCAN DataFlowUtil::ExprNode#class#ff OUTPUT In.1, In.0 'this'
    5520951  ~2%     {2} r6 = JOIN r5 WITH Instruction::Instruction::getConvertedResultExpression_dispred#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    5520950  ~0%     {2} r7 = JOIN r6 WITH Element::ElementBase::toString_dispred#ff@staged_ext ON FIRST 1 OUTPUT Lhs.1 'this', Rhs.1 'result'
    
    2317701  ~0%     {2} r8 = SCAN DataFlowPrivate::PrimaryArgumentNode#class#ff OUTPUT In.1, In.0 'this'
    
    2241169  ~0%     {2} r9 = JOIN r8 WITH Operand::PositionalArgumentOperand::getIndex_dispred#3#ff ON FIRST 1 OUTPUT Lhs.1 'this', ("Argument " ++ toString(Rhs.1))
    
    76532    ~1%     {2} r10 = JOIN r8 WITH Operand::ThisArgumentOperand#class#3#ffff ON FIRST 1 OUTPUT Lhs.1 'this', "This argument"
    
    2317701  ~0%     {2} r11 = r9 UNION r10
    7838651  ~0%     {2} r12 = r7 UNION r11
    8333552  ~0%     {2} r13 = r4 UNION r12
    
    20517434 ~4%     {2} r14 = DataFlowUtil::TOperandNode#ff@staged_ext AND NOT DataFlowPrivate::PrimaryArgumentNode#class#ff_0#antijoin_rhs(Lhs.1 'this')
    19269033 ~4%     {2} r15 = r14 AND NOT DataFlowPrivate::SideEffectArgumentNode#class#fff_0#antijoin_rhs(Lhs.1 'this')
    19269033 ~0%     {2} r16 = JOIN r15 WITH Operand::Operand::toString_dispred#ff ON FIRST 1 OUTPUT Lhs.1 'this', Rhs.1 'result'
    
    2392     ~2%     {2} r17 = DataFlowUtil::DefinitionByReferenceNode#class#ff AND NOT DataFlowUtil::Node::toString_dispred#ff#antijoin_rhs(Lhs.0 'this', Lhs.1)
    2392     ~3%     {2} r18 = SCAN r17 OUTPUT In.0 'this', "output argument"
    2392     ~3%     {2} r19 = STREAM DEDUP r18
    
    339416   ~0%     {2} r20 = SCAN DataFlowUtil::ParameterIndirectionNode#class#ff OUTPUT In.1, In.0 'this'
    340658   ~0%     {2} r21 = JOIN r20 WITH Instruction::VariableInstruction#3#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    340658   ~4%     {2} r22 = JOIN r21 WITH IRVariable::IRVariable::toString_dispred#2#ff ON FIRST 1 OUTPUT Lhs.1 'this', ("*" ++ Rhs.1)
    
    343050   ~4%     {2} r23 = r19 UNION r22
    19612083 ~0%     {2} r24 = r16 UNION r23
    
    10514309 ~2%     {2} r25 = JOIN DataFlowUtil::InstructionNode_not_DefinitionByReferenceNode_ExplicitParameterNode_ExprNode_ParameterIndirectionNode_ThisParameterNode#f WITH DataFlowUtil::TInstructionNode#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Rhs.0
    10514309 ~0%     {2} r26 = JOIN r25 WITH SSAConstruction::Cached::getInstructionOpcode#2#ff@staged_ext ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    10514309 ~3%     {2} r27 = JOIN r26 WITH Opcode::Opcode::toString_dispred#ff ON FIRST 1 OUTPUT Lhs.1 'this', Rhs.1 'result'
    
    1248401  ~0%     {2} r28 = SCAN DataFlowPrivate::SideEffectArgumentNode#class#fff OUTPUT In.2, In.0 'this'
    1248401  ~1%     {2} r29 = JOIN r28 WITH Instruction::IndexedInstruction#ff ON FIRST 1 OUTPUT Lhs.1 'this', ("Argument " ++ toString(Rhs.1) ++ " indirection")
    
    1252520  ~2%     {2} r30 = SCAN DataFlowUtil::DefinitionByReferenceNode#class#ff OUTPUT In.1, In.0 'this'
    1252520  ~3%     {2} r31 = JOIN r30 WITH Instruction::SideEffectInstruction::getPrimaryInstruction_dispred#3#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    1250513  ~5%     {2} r32 = JOIN r31 WITH Instruction::CallInstruction::getStaticCallTarget_dispred#3#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    1250509  ~0%     {2} r33 = JOIN r32 WITH Declaration::Declaration::getName_dispred#ff ON FIRST 1 OUTPUT Lhs.1 'this', (Rhs.1 ++ " output argument")
    
    2498910  ~2%     {2} r34 = r29 UNION r33
    13013219 ~4%     {2} r35 = r27 UNION r34
    32625302 ~4%     {2} r36 = r24 UNION r35
    40958854 ~2%     {2} r37 = r13 UNION r36
                     return r37
...
>>> Created relation DataFlowUtil::Node::toString_dispred#ff/2@f564a8 with 40957227 rows.

and with this PR:

(1403s) Tuple counts for DataFlowUtil::Node::toString_dispred#ff/2@b88dff:
    17746    ~1%     {2} r1 = SCAN DataFlowUtil::ThisParameterNode#class#ff OUTPUT In.0 'this', "this"
    17746    ~1%     {2} r2 = STREAM DEDUP r1
    
    477155   ~0%     {2} r3 = JOIN DataFlowUtil::ParameterNode::isParameterOf_dispred#fff#shared WITH Element::ElementBase::toString_dispred#ff@staged_ext ON FIRST 1 OUTPUT Lhs.1 'this', Rhs.1 'result'
    
    5520951  ~3%     {2} r4 = SCAN DataFlowUtil::ExprNode#class#ff OUTPUT In.1, In.0 'this'
    5520951  ~2%     {2} r5 = JOIN r4 WITH Instruction::Instruction::getConvertedResultExpression_dispred#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    5520950  ~0%     {2} r6 = JOIN r5 WITH Element::ElementBase::toString_dispred#ff@staged_ext ON FIRST 1 OUTPUT Lhs.1 'this', Rhs.1 'result'
    
    5998105  ~0%     {2} r7 = r3 UNION r6
    6015851  ~0%     {2} r8 = r2 UNION r7
    
    20517434 ~4%     {2} r9 = DataFlowUtil::TOperandNode#ff@staged_ext AND NOT DataFlowPrivate::PrimaryArgumentNode#class#ff_0#antijoin_rhs(Lhs.1 'this')
    19269033 ~4%     {2} r10 = r9 AND NOT DataFlowPrivate::SideEffectArgumentNode#class#fff_0#antijoin_rhs(Lhs.1 'this')
    19269033 ~6%     {2} r11 = JOIN r10 WITH Operand::Operand::toString_dispred#ff ON FIRST 1 OUTPUT Lhs.1 'this', Rhs.1 'result'
    
    2392     ~2%     {2} r12 = DataFlowUtil::DefinitionByReferenceNode#class#ff AND NOT DataFlowUtil::Node::toString_dispred#ff#antijoin_rhs(Lhs.0 'this', Lhs.1)
    2392     ~1%     {2} r13 = SCAN r12 OUTPUT In.0 'this', "output argument"
    2392     ~1%     {2} r14 = STREAM DEDUP r13
    
    19271425 ~6%     {2} r15 = r11 UNION r14
    
    339416   ~0%     {2} r16 = SCAN DataFlowUtil::ParameterIndirectionNode#class#ff OUTPUT In.1, In.0 'this'
    340658   ~0%     {2} r17 = JOIN r16 WITH Instruction::VariableInstruction#3#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    340658   ~0%     {2} r18 = JOIN r17 WITH IRVariable::IRVariable::toString_dispred#2#ff ON FIRST 1 OUTPUT Lhs.1 'this', ("*" ++ Rhs.1)
    
    10514309 ~2%     {2} r19 = JOIN DataFlowUtil::InstructionNode_not_DefinitionByReferenceNode_ExplicitParameterNode_ExprNode_ParameterIndirectionNode_ThisParameterNode#f WITH DataFlowUtil::TInstructionNode#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Rhs.0
    10514309 ~0%     {2} r20 = JOIN r19 WITH SSAConstruction::Cached::getInstructionOpcode#2#ff@staged_ext ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    10514309 ~0%     {2} r21 = JOIN r20 WITH Opcode::Opcode::toString_dispred#ff ON FIRST 1 OUTPUT Lhs.1 'this', Rhs.1 'result'
    
    10854967 ~0%     {2} r22 = r18 UNION r21
    30126392 ~3%     {2} r23 = r15 UNION r22
    36142243 ~0%     {2} r24 = r8 UNION r23
    
    11997    ~0%     {2} r25 = DataFlowPrivate::PrimaryArgumentNode#class#ff AND NOT DataFlowUtil::Node::toString_dispred#ff#antijoin_rhs#1(Lhs.0 'this', Lhs.1)
    
    11997    ~0%     {2} r26 = SCAN r25 OUTPUT In.1, In.0 'this'
    
    3196     ~0%     {2} r27 = JOIN r26 WITH Operand::PositionalArgumentOperand::getIndex_dispred#3#ff ON FIRST 1 OUTPUT Lhs.1 'this', ("Argument " ++ toString(Rhs.1))
    
    2317701  ~0%     {2} r28 = SCAN DataFlowPrivate::PrimaryArgumentNode#class#ff OUTPUT In.1, In.0 'this'
    2317701  ~4%     {2} r29 = JOIN r28 WITH Operand::Operand::getDef_dispred#3#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    2305704  ~2%     {2} r30 = JOIN r29 WITH Instruction::Instruction::getUnconvertedResultExpression_dispred#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    2305704  ~2%     {2} r31 = JOIN r30 WITH Element::ElementBase::toString_dispred#ff@staged_ext ON FIRST 1 OUTPUT Lhs.1 'this', Rhs.1 'result'
    
    8801     ~0%     {2} r32 = JOIN r26 WITH Operand::ThisArgumentOperand#class#3#ffff ON FIRST 1 OUTPUT Lhs.1 'this', "Argument this"
    
    2314505  ~1%     {2} r33 = r31 UNION r32
    2317701  ~1%     {2} r34 = r27 UNION r33
    
    4        ~0%     {3} r35 = SCAN DataFlowUtil::Node::toString_dispred#ff#shared OUTPUT In.1, -1, In.0 'this'
    0        ~0%     {2} r36 = JOIN r35 WITH Instruction::IndexedInstruction#ff ON FIRST 2 OUTPUT Lhs.2 'this', "Argument this indirection"
    
    4        ~0%     {2} r37 = DataFlowUtil::Node::toString_dispred#ff#shared AND NOT DataFlowUtil::Node::toString_dispred#ff#antijoin_rhs#3(Lhs.0 'this', Lhs.1)
    4        ~0%     {2} r38 = SCAN r37 OUTPUT In.1, In.0 'this'
    4        ~0%     {2} r39 = JOIN r38 WITH Instruction::IndexedInstruction#ff ON FIRST 1 OUTPUT Lhs.1 'this', ("Argument " ++ toString(Rhs.1) ++ " indirection")
    
    4        ~0%     {2} r40 = r36 UNION r39
    
    1248401  ~0%     {2} r41 = SCAN DataFlowPrivate::SideEffectArgumentNode#class#fff OUTPUT In.2, In.0 'this'
    1248397  ~2%     {2} r42 = JOIN r41 WITH Instruction::ReadSideEffectInstruction::getArgumentDef_dispred#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    1248397  ~0%     {2} r43 = JOIN r42 WITH Instruction::Instruction::getUnconvertedResultExpression_dispred#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    1248397  ~7%     {2} r44 = JOIN r43 WITH Element::ElementBase::toString_dispred#ff@staged_ext ON FIRST 1 OUTPUT Lhs.1 'this', (Rhs.1 'result' ++ " indirection")
    
    1252520  ~2%     {2} r45 = SCAN DataFlowUtil::DefinitionByReferenceNode#class#ff OUTPUT In.1, In.0 'this'
    1252520  ~3%     {2} r46 = JOIN r45 WITH Instruction::SideEffectInstruction::getPrimaryInstruction_dispred#3#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    1250513  ~5%     {2} r47 = JOIN r46 WITH Instruction::CallInstruction::getStaticCallTarget_dispred#3#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'this'
    1250509  ~7%     {2} r48 = JOIN r47 WITH Declaration::Declaration::getName_dispred#ff ON FIRST 1 OUTPUT Lhs.1 'this', (Rhs.1 ++ " output argument")
    
    2498906  ~4%     {2} r49 = r44 UNION r48
    2498910  ~4%     {2} r50 = r40 UNION r49
    4816611  ~2%     {2} r51 = r34 UNION r50
    40958854 ~0%     {2} r52 = r24 UNION r51
                     return r52
...
>>> Created relation DataFlowUtil::Node::toString_dispred#ff/2@b88dff with 40957227 rows.