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C#: Use Gvn comparison instead of StructuralComparisonConfiguration in UselessNullCoalescingExpression.

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This commit is contained in:
Michael Nebel
2022-03-10 12:45:48 +01:00
parent 4a1981edfd
commit 8e7c7d8259
1 changed files with 8 additions and 18 deletions
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26
csharp/ql/src/Language Abuse/UselessNullCoalescingExpression.ql
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@@ -14,24 +14,14 @@
import csharp
import semmle.code.csharp.commons.StructuralComparison
class StructuralComparisonConfig extends StructuralComparisonConfiguration {
StructuralComparisonConfig() { this = "UselessNullCoalescingExpression" }
override predicate candidate(ControlFlowElement x, ControlFlowElement y) {
exists(NullCoalescingExpr nce |
x.(Access) = nce.getLeftOperand() and
y.(Access) = nce.getRightOperand().getAChildExpr*()
)
}
NullCoalescingExpr getUselessNullCoalescingExpr() {
exists(AssignableAccess x |
result.getLeftOperand() = x and
forex(AssignableAccess y | same(x, y) | y instanceof AssignableRead and not y.isRefArgument())
)
}
private predicate uselessNullCoalescingExpr(NullCoalescingExpr nce) {
forex(AssignableAccess y |
y = nce.getRightOperand().getAChildExpr*() and sameGvn(nce.getLeftOperand(), y)
|
y instanceof AssignableRead and not y.isRefArgument()
)
}
from StructuralComparisonConfig c, NullCoalescingExpr nce
where nce = c.getUselessNullCoalescingExpr()
from NullCoalescingExpr nce
where uselessNullCoalescingExpr(nce)
select nce, "Both operands of this null-coalescing expression access the same variable or property."