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/**
* @name Useless comparison test
* @description A comparison that always evaluates to true or always evaluates to false may
* indicate faulty logic and dead code.
* @kind problem
* @problem.severity warning
* @id js/useless-comparison-test
* @tags quality
* reliability
* correctness
* @precision high
*/
import javascript
/**
* Holds if there are any contradictory guard nodes in `container`.
*
* We use this to restrict reachability analysis to a small set of containers.
*/
predicate hasContradictoryGuardNodes(StmtContainer container) {
exists(ConditionGuardNode guard |
RangeAnalysis::isContradictoryGuardNode(guard) and
container = guard.getContainer()
)
}
/**
* Holds if `block` is reachable and is in a container with contradictory guard nodes.
*/
predicate isReachable(BasicBlock block) {
exists(StmtContainer container |
hasContradictoryGuardNodes(container) and
block = container.getEntryBB()
)
or
isReachable(block.getAPredecessor()) and
not RangeAnalysis::isContradictoryGuardNode(block.getANode())
}
/**
* Holds if `block` is unreachable, but could be reached if `guard` was not contradictory.
*/
predicate isBlockedByContradictoryGuardNodes(BasicBlock block, ConditionGuardNode guard) {
RangeAnalysis::isContradictoryGuardNode(guard) and
isReachable(block.getAPredecessor()) and // the guard itself is reachable
block = guard.getBasicBlock()
or
isBlockedByContradictoryGuardNodes(block.getAPredecessor(), guard) and
not isReachable(block)
}
/**
* Holds if the given guard node is contradictory and causes an expression or statement to be unreachable.
*/
predicate isGuardNodeWithDeadCode(ConditionGuardNode guard) {
exists(BasicBlock block |
isBlockedByContradictoryGuardNodes(block, guard) and
block.getANode() instanceof ExprOrStmt
)
}
from ConditionGuardNode guard
where isGuardNodeWithDeadCode(guard)
select guard.getTest(),
"The condition '" + guard.getTest() + "' is always " + guard.getOutcome().booleanNot() + "."