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[Draft] Allow constant folding to fold equals operator #821

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[Draft] Allow constant folding to fold equals operator #821

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29 changes: 29 additions & 0 deletions optimizer/src/main/java/dev/cel/optimizer/optimizers/ConstantFoldingOptimizer.java
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Original file line number Diff line number Diff line change
Expand Up @@ -167,6 +167,10 @@ private boolean canFold(CelNavigableMutableExpr navigableExpr) {
&& cond.constant().getKind().equals(CelConstant.Kind.BOOLEAN_VALUE);
}

if (functionName.equals(Operator.EQUALS.getFunction())) {
return mutableCall.args().stream().anyMatch(x -> isExprConstantOfKind(x, CelConstant.Kind.BOOLEAN_VALUE));
}

if (functionName.equals(Operator.IN.getFunction())) {
return canFoldInOperator(navigableExpr);
}
Expand Down Expand Up @@ -393,6 +397,27 @@ private Optional<CelMutableAst> maybePruneBranches(
}
}
}
} else if (function.equals(Operator.EQUALS.getFunction())) {
CelMutableExpr lhs = call.args().get(0);
CelMutableExpr rhs = call.args().get(1);
boolean lhsIsBoolean = isExprConstantOfKind(lhs, CelConstant.Kind.BOOLEAN_VALUE);
boolean rhsIsBoolean = isExprConstantOfKind(rhs, CelConstant.Kind.BOOLEAN_VALUE);
Optional<CelMutableExpr> branchToRetain = Optional.empty();

if (lhsIsBoolean && rhsIsBoolean) {
boolean result = lhs.constant().booleanValue() == rhs.constant().booleanValue();
branchToRetain = Optional.of(CelMutableExpr.ofConstant(CelConstant.ofValue(result)));
} else if (lhsIsBoolean) {
branchToRetain = Optional.of(lhs.constant().booleanValue() ? rhs : lhs);
} else if (rhsIsBoolean) {
branchToRetain = Optional.of(rhs.constant().booleanValue() ? lhs : rhs);
}

return branchToRetain.map(node ->
astMutator.replaceSubtree(
mutableAst,
node,
expr.id()));
}

return Optional.empty();
Expand Down Expand Up @@ -663,6 +688,10 @@ public static Builder newBuilder() {
ConstantFoldingOptions() {}
}

private static boolean isExprConstantOfKind(CelMutableExpr expr, CelConstant.Kind constantKind) {
return expr.getKind().equals(Kind.CONSTANT) && expr.constant().getKind().equals(constantKind);
}

private ConstantFoldingOptimizer(ConstantFoldingOptions constantFoldingOptions) {
this.constantFoldingOptions = constantFoldingOptions;
this.astMutator = AstMutator.newInstance(constantFoldingOptions.maxIterationLimit());
Expand Down
8 changes: 8 additions & 0 deletions optimizer/src/test/java/dev/cel/optimizer/optimizers/ConstantFoldingOptimizerTest.java
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Expand Up @@ -189,6 +189,14 @@ public class ConstantFoldingOptimizerTest {
@TestParameters("{source: 'sets.contains([1], [1])', expected: 'true'}")
@TestParameters(
"{source: 'cel.bind(r0, [1, 2, 3], cel.bind(r1, 1 in r0, r1))', expected: 'true'}")
@TestParameters("{source: 'x == true', expected: 'x'}")
@TestParameters("{source: 'true == x', expected: 'x'}")
@TestParameters("{source: 'x == false', expected: 'false'}")
@TestParameters("{source: 'false == x', expected: 'false'}")
@TestParameters("{source: 'true == false', expected: 'false'}")
@TestParameters("{source: 'true == true', expected: 'true'}")
@TestParameters("{source: 'false == true', expected: 'false'}")
@TestParameters("{source: 'false == false', expected: 'true'}")
// TODO: Support folding lists with mixed types. This requires mutable lists.
// @TestParameters("{source: 'dyn([1]) + [1.0]'}")
public void constantFold_success(String source, String expected) throws Exception {
Expand Down
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