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JavaScript: Refactor UselessConditional for performance.

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This commit is contained in:
Max Schaefer
2018-11-30 12:28:01 +00:00
parent 8b8b352439
commit 627583fffa
1 changed files with 14 additions and 5 deletions
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19
javascript/ql/src/Statements/UselessConditional.ql
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@@ -17,6 +17,17 @@ import semmle.javascript.RestrictedLocations
import semmle.javascript.dataflow.Refinements
import semmle.javascript.DefensiveProgramming
/**
* Gets the unique definition of `v`.
*
* If `v` has no definitions or more than one, or if its single definition
* is a destructuring assignment, this predicate is undefined.
*/
VarDef getSingleDef(Variable v) {
strictcount(VarDef vd | vd.getAVariable() = v) = 1 and
result.getTarget() = v.getAReference()
}
/**
* Holds if variable `v` looks like a symbolic constant, that is, it is assigned
* exactly once, either in a `const` declaration or with a constant initializer.
@@ -24,11 +35,9 @@ import semmle.javascript.DefensiveProgramming
* We do not consider conditionals to be useless if they check a symbolic constant.
*/
predicate isSymbolicConstant(Variable v) {
// defined exactly once
count(VarDef vd | vd.getAVariable() = v) = 1 and
// the definition is either a `const` declaration or it assigns a constant to it
exists(VarDef vd | vd.getAVariable() = v and count(vd.getAVariable()) = 1 |
vd.(VariableDeclarator).getDeclStmt() instanceof ConstDeclStmt or
exists(VarDef vd | vd = getSingleDef(v) |
vd.(VariableDeclarator).getDeclStmt() instanceof ConstDeclStmt
or
isConstant(vd.getSource())
)
}