C++: Create a common base class for 'FieldContent' and 'UnionContent'#20862
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MathiasVP merged 6 commits intogithub:mainfrom Nov 20, 2025
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…t supposed to have abstract public stuff. Oops ...
…nt' called 'FieldContent'.
```
Evaluated relational algebra for predicate DataFlowPrivate::storeStepImpl/4#b2c79f9a@13be12rc with tuple counts:
9 ~0% {3} r1 = JOIN `FlowSummaryImpl::Private::Steps::summaryStoreStep/3#5c2d4899` WITH DataFlowUtil::TFlowSummaryNode#40da8361 ON FIRST 1 OUTPUT Lhs.2, Lhs.1, Rhs.1
9 ~0% {4} | JOIN WITH DataFlowUtil::TFlowSummaryNode#40da8361 ON FIRST 1 OUTPUT Lhs.2, Lhs.1, Rhs.1, _
9 ~12% {4} | REWRITE WITH Out.3 := true
1853420 ~0% {3} r2 = SCAN `DataFlowPrivate::nodeHasInstruction/3#f469bb06` OUTPUT In.1, In.0, In.2
100282 ~0% {3} | JOIN WITH `Instruction::StoreInstruction.getDestinationAddressOperand/0#dispred#596a4aba` ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2
127910 ~0% {6} | JOIN WITH `DataFlowPrivate::numberOfLoadsFromOperand/4#7e555666_1023#join_rhs` ON FIRST 1 OUTPUT _, Lhs.1, Rhs.1, Rhs.3, Lhs.2, Rhs.2
127910 ~0% {4} | REWRITE WITH Tmp.0 := 1, Out.0 := (Tmp.0 + In.4 + In.5) KEEPING 4
4178182721 ~1% {4} | JOIN WITH `DataFlowUtil::FieldContent.getIndirectionIndex/0#dispred#cc69866f_10#join_rhs` ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2, Lhs.3
4290552803 ~0% {5} | JOIN WITH `DataFlowUtil::FieldContent.getAField/0#dispred#ba1c91e5` ON FIRST 1 OUTPUT Lhs.2, Lhs.1, Lhs.3, Lhs.0, Rhs.1
3033745816 ~5% {7} | JOIN WITH DataFlowUtil::PostFieldUpdateNode#b86f3a84_1023#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.2, Lhs.3, Lhs.4, Rhs.2, Rhs.3
3033745816 ~3% {9} | JOIN WITH DataFlowUtil::TPostUpdateNodeImpl#f5e76b7a_21#join_rhs ON FIRST 1 OUTPUT Lhs.1, Lhs.2, Lhs.3, Lhs.4, Lhs.0, Lhs.5, Lhs.6, Rhs.1, _
{8} | REWRITE WITH Tmp.8 := 1, TEST InOut.7 = Tmp.8 KEEPING 8
1516872908 ~0% {7} | SCAN OUTPUT In.4, In.5, In.6, In.0, In.1, In.2, In.3
2409090286 ~1% {6} | JOIN WITH DataFlowUtil::PostFieldUpdateNode#b86f3a84_0231#join_rhs ON FIRST 3 OUTPUT Rhs.3, Lhs.6, Lhs.3, Lhs.4, Lhs.5, Lhs.0
66016 ~45% {4} | JOIN WITH `DataFlowUtil::FieldAddress.getField/0#dispred#bdd01c1a` ON FIRST 2 OUTPUT Lhs.2, Lhs.4, Lhs.5, Lhs.3
66025 ~45% {4} r3 = r1 UNION r2
return r3
```
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Pull Request Overview
This PR refactors the dataflow content hierarchy by introducing a common base class FieldContent that unifies handling of both union and non-union field accesses. This simplifies querying for field accesses since callers no longer need to check whether they're dealing with a union or struct field.
Key changes:
- Introduced
FieldContentas a common base class withgetAField()andgetField()methods - Renamed the original
FieldContenttoNonUnionFieldContent - Made
UnionContentextend the newFieldContentbase class
Reviewed Changes
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| File | Description |
|---|---|
| cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowUtil.qll | Introduces the new type hierarchy with FieldContent as base class, renames FieldContent to NonUnionFieldContent, and makes UnionContent extend FieldContent |
| cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowPrivate.qll | Updates store and read steps to use unified FieldContent type, simplifying the logic by using getAField() method; adds helper function for late-binding indirection index |
| cpp/ql/src/utils/modelgenerator/internal/CaptureModels.qll | Updates references to use NonUnionFieldContent where specific type is needed and simplifies isField predicate to use the new base class |
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I was writing a Microsoft query and was once again bitten by the fact that, when you look at a field access such as:
The read step from
xtofis probably a step that reads aDataFlow::FieldContent... but it may also be reading aDataFlow::UnionContent. And in order to know which one to use you have to check the type ofx.This PR improves this experience by making
FieldContentwork for both union and non-union fields. It even simplifies some of the internal dataflow code as well 🎉There should be no observable changes as a result of this (other than
FieldContentnow magically starts working for unions as well).Commit-by-commit review recommended.