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212 changes: 193 additions & 19 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 @@ -38,6 +38,7 @@
import dev.cel.common.ast.CelMutableExpr.CelMutableCall;
import dev.cel.common.ast.CelMutableExpr.CelMutableList;
import dev.cel.common.ast.CelMutableExpr.CelMutableMap;
import dev.cel.common.ast.CelMutableExpr.CelMutableSelect;
import dev.cel.common.ast.CelMutableExpr.CelMutableStruct;
import dev.cel.common.ast.CelMutableExprConverter;
import dev.cel.common.internal.DateTimeHelpers;
Expand All @@ -55,7 +56,6 @@
import dev.cel.common.values.StructValue;
import dev.cel.extensions.CelOptionalLibrary.Function;
import dev.cel.optimizer.AstMutator;
import dev.cel.optimizer.AstMutator.SubtreeReplacement;
import dev.cel.optimizer.CelAstOptimizer;
import dev.cel.optimizer.CelOptimizationException;
import dev.cel.runtime.CelAttributePattern;
Expand All @@ -73,6 +73,7 @@
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import org.jspecify.annotations.Nullable;

/**
Expand Down Expand Up @@ -141,7 +142,7 @@ public OptimizationResult optimize(CelAbstractSyntaxTree ast, Cel cel)
ImmutableMap<String, CelType> identTypes = precomputeIdentTypes(initialMutableAst);

CelMutableAst mutableAst =
foldConstants(optimizerEnv, valueProvider, identTypes, initialMutableAst);
foldConstants(cel, optimizerEnv, valueProvider, identTypes, initialMutableAst);
mutableAst = pruneOptionalElements(mutableAst);

if (mutableAst == initialMutableAst) {
Expand Down Expand Up @@ -172,23 +173,25 @@ private static ImmutableMap<String, CelType> precomputeIdentTypes(CelMutableAst
}

private CelMutableAst foldConstants(
Cel cel,
Cel optimizerEnv,
@Nullable CelValueProvider valueProvider,
ImmutableMap<String, CelType> identTypes,
CelMutableAst mutableAst)
throws CelOptimizationException {
for (int iterCount = 0; iterCount < constantFoldingOptions.maxIterationLimit(); iterCount++) {
Optional<SubtreeReplacement> replacement =
findNextFoldableSubtree(optimizerEnv, valueProvider, identTypes, mutableAst);
if (!replacement.isPresent()) {
Optional<CelMutableAst> nextAst =
findNextFoldableSubtree(cel, optimizerEnv, valueProvider, identTypes, mutableAst);
if (!nextAst.isPresent()) {
return mutableAst;
}
mutableAst = astMutator.replaceSubtree(mutableAst, replacement.get());
mutableAst = nextAst.get();
}
throw new IllegalStateException("Max iteration count reached.");
}

private Optional<SubtreeReplacement> findNextFoldableSubtree(
private Optional<CelMutableAst> findNextFoldableSubtree(
Cel cel,
Cel optimizerEnv,
@Nullable CelValueProvider valueProvider,
ImmutableMap<String, CelType> identTypes,
Expand All @@ -199,19 +202,40 @@ private Optional<SubtreeReplacement> findNextFoldableSubtree(
navAst.getRoot().allNodes(TraversalOrder.PRE_ORDER).filter(this::canFold).iterator();
while (foldableExprs.hasNext()) {
CelNavigableMutableExpr foldableExpr = foldableExprs.next();
Optional<CelMutableExpr> pruned =
Optional<CelMutableExpr> candidate =
maybePruneBranches(mutableAst, identTypes, foldableExpr.expr());
if (pruned.isPresent()) {
return Optional.of(SubtreeReplacement.of(foldableExpr.id(), pruned.get()));
if (!candidate.isPresent()) {
candidate = maybeFold(optimizerEnv, valueProvider, foldableExpr);
}
Optional<CelMutableExpr> folded = maybeFold(optimizerEnv, valueProvider, foldableExpr);
if (folded.isPresent()) {
return Optional.of(SubtreeReplacement.of(foldableExpr.id(), folded.get()));
if (candidate.isPresent()) {
Optional<CelMutableAst> replacedAst =
tryReplaceSubtree(cel, optimizerEnv, mutableAst, foldableExpr, candidate.get());
if (replacedAst.isPresent()) {
return replacedAst;
}
}
}
return Optional.empty();
}

private Optional<CelMutableAst> tryReplaceSubtree(
Cel cel,
Cel optimizerEnv,
CelMutableAst mutableAst,
CelNavigableMutableExpr foldableExpr,
CelMutableExpr candidate) {
// Folding an expression containing a dynamic identifier can narrow its static type from dyn to
// a concrete type (e.g. `false || [3, x][0]` -> `false || 3`), which may cause the enclosing
// expression or expected result type to fail type-checking.
CelMutableAst candidateAst =
astMutator.replaceSubtree(
CelMutableAst.fromCelAst(mutableAst.toParsedAst()), candidate, foldableExpr.id());
Cel envToCheck = foldableExpr.parent().isPresent() ? optimizerEnv : cel;
return envToCheck.check(candidateAst.toParsedAst()).hasError()
? Optional.empty()
: Optional.of(candidateAst);
}

private boolean canFold(CelNavigableMutableExpr navigableExpr) {
switch (navigableExpr.getKind()) {
case CALL:
Expand Down Expand Up @@ -269,19 +293,61 @@ private boolean canFold(CelNavigableMutableExpr navigableExpr) {
return !CelNavigableExprUtil.hasComprehensionVariable(navigableExpr);
}

// Default case: all call arguments must be constants. If the argument is a container (ex:
// list, map), then its arguments must be a constant.
return areChildrenArgConstant(navigableExpr);
return areChildrenArgConstant(navigableExpr)
|| maybePruneContainerLookup(navigableExpr.expr()).isPresent()
|| maybePruneOptionalCall(mutableCall).isPresent();
case SELECT:
CelNavigableMutableExpr operand = navigableExpr.children().collect(onlyElement());
return areChildrenArgConstant(operand);
return areChildrenArgConstant(operand)
|| maybePruneContainerLookup(navigableExpr.expr()).isPresent();
case COMPREHENSION:
return !isNestedComprehension(navigableExpr) && containsFoldableFunctionOnly(navigableExpr);
default:
return false;
}
}

private static boolean isErrorFree(CelMutableExpr expr) {
switch (expr.getKind()) {
case CONSTANT:
case IDENT:
return true;
case CALL:
CelMutableCall call = expr.call();
return call.function().equals(Function.OPTIONAL_NONE.getFunction())
|| (call.function().equals(Function.OPTIONAL_OF.getFunction())
&& isErrorFree(call.args().get(0)));
case LIST:
CelMutableList list = expr.list();
return list.optionalIndices().isEmpty()
&& list.elements().stream().allMatch(ConstantFoldingOptimizer::isErrorFree);
case MAP:
return isErrorFreeMap(expr.map());
default:
return false;
}
}

private static boolean isErrorFreeMap(CelMutableMap map) {
Set<CelConstant> keysSeen = new HashSet<>();
for (CelMutableMap.Entry entry : map.entries()) {
if (entry.optionalEntry()
|| !entry.key().getKind().equals(Kind.CONSTANT)
|| !isErrorFree(entry.value())
|| !keysSeen.add(normalizeMapKey(entry.key().constant()))) {
return false;
}
}
return true;
}

private static CelConstant normalizeMapKey(CelConstant key) {
if (key.getKind().equals(CelConstant.Kind.UINT64_VALUE) && key.uint64Value().longValue() >= 0) {
return CelConstant.ofValue(key.uint64Value().longValue());
}
return key;
}

private boolean containsFoldableFunctionOnly(CelNavigableMutableExpr navigableExpr) {
return navigableExpr
.allNodes()
Expand Down Expand Up @@ -334,7 +400,13 @@ private Optional<CelMutableExpr> maybeFold(
Object result;
try {
result = evaluateExpr(cel, node);
} catch (CelEvaluationException | CelValidationException e) {
} catch (CelValidationException | CelEvaluationException e) {
if (node.getKind().equals(Kind.COMPREHENSION)) {
// Comprehension may fail to evaluate due to other unknowns the expression references. We'll
// simply opt to not fold the subtree and move on.
return Optional.empty();
}

throw new CelOptimizationException(
"Constant folding failure. Failed to evaluate subtree due to: " + e.getMessage(), e);
}
Expand Down Expand Up @@ -479,7 +551,7 @@ private static boolean isCallToFunction(CelMutableExpr expr, String functionName
private Optional<CelMutableExpr> maybePruneBranches(
CelMutableAst mutableAst, Map<String, CelType> identTypes, CelMutableExpr expr) {
if (!expr.getKind().equals(Kind.CALL)) {
return Optional.empty();
return maybePruneContainerLookup(expr);
}

CelMutableCall call = expr.call();
Expand Down Expand Up @@ -575,6 +647,108 @@ private Optional<CelMutableExpr> maybePruneBranches(
return replacementExpr;
}

Optional<CelMutableExpr> containerLookup = maybePruneContainerLookup(expr);
return containerLookup.isPresent() ? containerLookup : maybePruneOptionalCall(call);
}

private static Optional<CelMutableExpr> maybePruneOptionalCall(CelMutableCall call) {
if (!call.target().isPresent()) {
return Optional.empty();
}
String function = call.function();
CelMutableExpr target = call.target().get();
if (function.equals(Function.OR.getFunction())
|| function.equals(Function.OR_VALUE.getFunction())) {
CelMutableExpr arg = call.args().get(0);
if (isCallToFunction(target, Function.OPTIONAL_NONE.getFunction())) {
return Optional.of(arg);
}
if (isCallToFunction(target, Function.OPTIONAL_OF.getFunction())
&& isErrorFree(target)
&& isErrorFree(arg)) {
return Optional.of(
function.equals(Function.OR.getFunction()) ? target : target.call().args().get(0));
}
} else if (function.equals(Function.VALUE.getFunction())) {
if (isCallToFunction(target, Function.OPTIONAL_OF.getFunction()) && isErrorFree(target)) {
return Optional.of(target.call().args().get(0));
}
} else if (function.equals(Function.HAS_VALUE.getFunction())) {
if (isCallToFunction(target, Function.OPTIONAL_NONE.getFunction())) {
return Optional.of(CelMutableExpr.ofConstant(CelConstant.ofValue(false)));
}
if (isCallToFunction(target, Function.OPTIONAL_OF.getFunction()) && isErrorFree(target)) {
return Optional.of(CelMutableExpr.ofConstant(CelConstant.ofValue(true)));
}
}
return Optional.empty();
}

private static Optional<CelMutableExpr> maybePruneContainerLookup(CelMutableExpr expr) {
if (expr.getKind().equals(Kind.SELECT)) {
CelMutableSelect select = expr.select();
if (select.operand().getKind().equals(Kind.MAP) && isErrorFreeMap(select.operand().map())) {
Optional<CelMutableExpr> val =
findMapEntryByConstantKey(select.operand().map(), CelConstant.ofValue(select.field()));
return select.testOnly()
? Optional.of(CelMutableExpr.ofConstant(CelConstant.ofValue(val.isPresent())))
: val;
}
return Optional.empty();
}
if (!expr.getKind().equals(Kind.CALL)) {
return Optional.empty();
}
CelMutableCall call = expr.call();
String function = call.function();
if (function.equals(Operator.INDEX.getFunction())) {
return findContainerElement(call.args().get(0), call.args().get(1), /* optional= */ false);
}
if (function.equals(Operator.OPTIONAL_INDEX.getFunction())
|| function.equals(Operator.OPTIONAL_SELECT.getFunction())) {
return findContainerElement(call.args().get(0), call.args().get(1), /* optional= */ true);
}
return Optional.empty();
}

private static Optional<CelMutableExpr> findContainerElement(
CelMutableExpr target, CelMutableExpr key, boolean optional) {
Optional<CelMutableExpr> elem;
if (target.getKind().equals(Kind.LIST)
&& isErrorFree(target)
&& isExprConstantOfKind(key, CelConstant.Kind.INT64_VALUE)) {
long idx = key.constant().int64Value();
List<CelMutableExpr> elements = target.list().elements();
elem =
idx >= 0 && idx < elements.size()
? Optional.of(elements.get((int) idx))
: Optional.empty();
} else if (target.getKind().equals(Kind.MAP)
&& isErrorFreeMap(target.map())
&& key.getKind().equals(Kind.CONSTANT)) {
elem = findMapEntryByConstantKey(target.map(), key.constant());
} else {
return Optional.empty();
}
if (!optional) {
return elem;
}
return Optional.of(
elem.map(
val ->
CelMutableExpr.ofCall(
CelMutableCall.create(Function.OPTIONAL_OF.getFunction(), val)))
.orElseGet(ConstantFoldingOptimizer::newOptionalNoneExpr));
}

private static Optional<CelMutableExpr> findMapEntryByConstantKey(
CelMutableMap map, CelConstant targetKey) {
CelConstant normalizedTarget = normalizeMapKey(targetKey);
for (CelMutableMap.Entry entry : map.entries()) {
if (normalizeMapKey(entry.key().constant()).equals(normalizedTarget)) {
return Optional.of(entry.value());
}
}
return Optional.empty();
}

Expand Down
2 changes: 2 additions & 0 deletions optimizer/src/test/java/dev/cel/optimizer/optimizers/BUILD.bazel
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,8 @@ java_library(
"@maven//:com_google_testparameterinjector_test_parameter_injector",
"//:java_truth",
"@maven//:com_google_truth_extensions_truth_proto_extension",
"//verifier",
"//verifier:verifier_factory",
"@cel_spec//proto/cel/expr:syntax_java_proto",
"@cel_spec//proto/cel/expr/conformance/proto2:test_all_types_java_proto",
"@cel_spec//proto/cel/expr/conformance/proto3:test_all_types_java_proto",
Expand Down
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