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Merge pull request #4544 from tausbn/python-fix-bad-join-in-use-use-ssa

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Python: Fix bad join order in `adjacentUseUseSameVar`
This commit is contained in:
Rasmus Wriedt Larsen
2020-10-23 14:37:27 +02:00
committed by GitHub
parent bbda22c769 6d81ca12c4
commit 7993a83750
1 changed files with 27 additions and 3 deletions
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30
python/ql/src/semmle/python/essa/SsaCompute.qll
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@@ -431,6 +431,31 @@ private module SsaComputeImpl {
defSourceUseRank(v, b2, 1, i2)
}
/**
* Holds if `use1` is a use of the variable `v`, and there exists an adjacent reference to `v`
* in basic block `b1` at index `i1`.
*
* A helper predicate for `adjacentUseUseSameVar`, to prevent the first join from being between
* the two instances of `variableSourceUse` in
* ```ql
* exists(SsaSourceVariable v, BasicBlock b1, int i1, BasicBlock b2, int i2 |
* adjacentVarRefs(v, b1, i1, b2, i2) and
* variableSourceUse(v, use1, b1, i1) and
* variableSourceUse(v, use2, b2, i2)
* )
* ```
*/
pragma[nomagic]
cached
private predicate adjacentRefUse(
SsaSourceVariable v, BasicBlock b2, int i2, ControlFlowNode use1
) {
exists(BasicBlock b1, int i1 |
adjacentVarRefs(v, b1, i1, b2, i2) and
variableSourceUse(v, use1, b1, i1)
)
}
/**
* Holds if `use1` and `use2` form an adjacent use-use-pair of the same SSA
* variable, that is, the value read in `use1` can reach `use2` without passing
@@ -438,9 +463,8 @@ private module SsaComputeImpl {
*/
cached
predicate adjacentUseUseSameVar(ControlFlowNode use1, ControlFlowNode use2) {
exists(SsaSourceVariable v, BasicBlock b1, int i1, BasicBlock b2, int i2 |
adjacentVarRefs(v, b1, i1, b2, i2) and
variableSourceUse(v, use1, b1, i1) and
exists(SsaSourceVariable v, BasicBlock b2, int i2 |
adjacentRefUse(v, b2, i2, use1) and
variableSourceUse(v, use2, b2, i2)
)
}