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C++: Add more comments to describe the constant expression hack.

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Mathias Vorreiter Pedersen
2025-09-25 12:43:57 +01:00
parent 5b5c1de05b
commit 04ce4057e1
1 changed files with 6 additions and 1 deletions
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7
cpp/ql/lib/semmle/code/cpp/controlflow/IRGuards.qll
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@@ -97,9 +97,14 @@ module GuardsInput implements SharedGuards::InputSig<Cpp::Location, Instruction,
this.(ConstantInstruction).getValue().toInt() = value and this.(ConstantInstruction).getValue().toInt() = value and
this.getResultIRType() instanceof IRIntegerType this.getResultIRType() instanceof IRIntegerType
or or
// In order to have an "integer constant" for a switch case // In order to have an integer constant for a switch case
// we misuse the first instruction (which is always a NoOp instruction) // we misuse the first instruction (which is always a NoOp instruction)
// as a constant with the switch case's value. // as a constant with the switch case's value.
// Even worse, since we need a case range to generate an `TIntRange`
// guard value we must ensure that there exists `ConstantExpr`s whose
// integer value is the end-points. So we let this constant expression
// have both end-point values. Luckily, these `NoOp` instructions do not
// interact with SSA in any way. So this should not break anything.
exists(CaseEdge edge | this = any(SwitchInstruction switch).getSuccessor(edge) | exists(CaseEdge edge | this = any(SwitchInstruction switch).getSuccessor(edge) |
value = edge.getMaxValue().toInt() value = edge.getMaxValue().toInt()
or or