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C++: Add isLiveAtEndOfBlock predicate to Ssa::Definition #21202

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MathiasVP merged 2 commits into from
Jan 21, 2026
+19 −1
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C++: Add isLiveAtEndOfBlock predicate to Ssa::Definition #21202

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d89967c
C++: Add ''isLiveAtEndOfBlock' predicate to 'Definition'.
MathiasVP Jan 21, 2026
60ee92d
C++: Drive-by fix: Don't use the uncached ''getAPhiInputOrPriorDefini…
MathiasVP Jan 21, 2026
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20 changes: 19 additions & 1 deletion cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/SsaImpl.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -940,6 +940,16 @@ module SsaCached {
SsaImpl::phiHasInputFromBlock(phi, inp, bb)
}

cached
predicate uncertainWriteDefinitionInput(Definition uncertain, Definition inp) {
SsaImpl::uncertainWriteDefinitionInput(uncertain, inp)
}

cached
predicate ssaDefReachesEndOfBlock(IRBlock bb, Definition def) {
SsaImpl::ssaDefReachesEndOfBlock(bb, def, _)
}

predicate variableRead = SsaInput::variableRead/4;

predicate variableWrite = SsaInput::variableWrite/4;
Expand Down Expand Up @@ -1173,9 +1183,17 @@ class Definition extends SsaImpl::Definition {
private Definition getAPhiInputOrPriorDefinition() {
result = this.(PhiNode).getAnInput()
or
SsaImpl::uncertainWriteDefinitionInput(this, result)
uncertainWriteDefinitionInput(this, result)
}

/**
* Holds if this SSA definition is live at the end of basic block `bb`.
* That is, this definition reaches the end of basic block `bb`, at which
* point it is still live, without crossing another SSA definition of the
* same source variable.
*/
predicate isLiveAtEndOfBlock(IRBlock bb) { ssaDefReachesEndOfBlock(bb, this) }

/**
* Gets a definition that ultimately defines this SSA definition and is
* not itself a phi node.
Expand Down
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