com.google.javascript.jscomp.AggressiveInlineAliases Maven / Gradle / Ivy
Show all versions of closure-compiler-linter Show documentation
/*
* Copyright 2016 The Closure Compiler Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.javascript.jscomp;
import com.google.common.base.Preconditions;
import com.google.common.base.Predicates;
import com.google.javascript.jscomp.GlobalNamespace.AstChange;
import com.google.javascript.jscomp.GlobalNamespace.Name;
import com.google.javascript.jscomp.GlobalNamespace.Ref;
import com.google.javascript.jscomp.GlobalNamespace.Ref.Type;
import com.google.javascript.jscomp.ReferenceCollectingCallback.Reference;
import com.google.javascript.jscomp.ReferenceCollectingCallback.ReferenceCollection;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
/**
* Inlines type aliases if they are explicitly or effectively const.
*
* This frees subsequent optimization passes from the responsibility of having to reason about
* alias chains and is a requirement for correct behavior in at least CollapseProperties and
* J2clPropertyInlinerPass.
*/
class AggressiveInlineAliases implements CompilerPass {
static final DiagnosticType UNSAFE_CTOR_ALIASING =
DiagnosticType.warning(
"JSC_UNSAFE_CTOR_ALIASING",
"Variable {0} aliases a constructor, " + "so it cannot be assigned multiple times");
/**
* @param name The Name whose properties references should be updated.
* @param value The value to use when rewriting.
* @param depth The chain depth.
* @param newNodes Expression nodes that have been updated.
*/
private void rewriteAliasProps(Name name, Node value, int depth, Set newNodes) {
if (name.props == null) {
return;
}
Preconditions.checkState(
!value.matchesQualifiedName(name.getFullName()),
"%s should not match name %s",
value,
name.getFullName());
for (Name prop : name.props) {
rewriteAliasProps(prop, value, depth + 1, newNodes);
List refs = new ArrayList<>(prop.getRefs());
for (Ref ref : refs) {
Node target = ref.node;
for (int i = 0; i <= depth; i++) {
if (target.isGetProp()) {
target = target.getFirstChild();
} else if (NodeUtil.isObjectLitKey(target)) {
// Object literal key definitions are a little trickier, as we
// need to find the assignment target
Node gparent = target.getGrandparent();
if (gparent.isAssign()) {
target = gparent.getFirstChild();
} else {
Preconditions.checkState(NodeUtil.isObjectLitKey(gparent));
target = gparent;
}
} else {
throw new IllegalStateException("unexpected: " + target);
}
}
Preconditions.checkState(target.isGetProp() || target.isName());
Node newValue = value.cloneTree();
target.replaceWith(newValue);
compiler.reportChangeToEnclosingScope(newValue);
prop.removeRef(ref);
// Rescan the expression root.
newNodes.add(new AstChange(ref.module, ref.scope, ref.node));
}
}
}
private AbstractCompiler compiler;
private boolean codeChanged;
AggressiveInlineAliases(AbstractCompiler compiler) {
this.compiler = compiler;
this.codeChanged = true;
}
@Override
public void process(Node externs, Node root) {
while (this.codeChanged) {
this.codeChanged = false;
GlobalNamespace namespace = new GlobalNamespace(compiler, root);
inlineAliases(namespace);
}
}
private JSModule getRefModule(ReferenceCollectingCallback.Reference ref) {
CompilerInput input = compiler.getInput(ref.getInputId());
return input == null ? null : input.getModule();
}
/**
* For each qualified name N in the global scope, we check if: (a) No ancestor of N is ever
* aliased or assigned an unknown value type. (If N = "a.b.c", "a" and "a.b" are never aliased).
* (b) N has exactly one write, and it lives in the global scope. (c) N is aliased in a local
* scope. (d) N is aliased in global scope
*
* If (a) is true, then GlobalNamespace must know all the writes to N. If (a) and (b) are true,
* then N cannot change during the execution of a local scope. If (a) and (b) and (c) are true,
* then the alias can be inlined if the alias obeys the usual rules for how we decide whether a
* variable is inlineable. If (a) and (b) and (d) are true, then inline the alias if possible (if
* it is assigned exactly once unconditionally).
*
* @see InlineVariables
*/
private void inlineAliases(GlobalNamespace namespace) {
// Invariant: All the names in the worklist meet condition (a).
Deque workList = new ArrayDeque<>(namespace.getNameForest());
while (!workList.isEmpty()) {
Name name = workList.pop();
// Don't attempt to inline a getter or setter property as a variable.
if (name.type == Name.Type.GET || name.type == Name.Type.SET) {
continue;
}
if (!name.inExterns && name.globalSets == 1 && name.localSets == 0 && name.aliasingGets > 0) {
// {@code name} meets condition (b). Find all of its local aliases
// and try to inline them.
List refs = new ArrayList<>(name.getRefs());
for (Ref ref : refs) {
if (ref.type == Type.ALIASING_GET && ref.scope.isLocal()) {
// {@code name} meets condition (c). Try to inline it.
// TODO(johnlenz): consider picking up new aliases at the end
// of the pass instead of immediately like we do for global
// inlines.
if (inlineAliasIfPossible(name, ref, namespace)) {
name.removeRef(ref);
}
} else if (ref.type == Type.ALIASING_GET
&& ref.scope.isGlobal()
&& ref.getTwin() == null) { // ignore aliases in chained assignments
if (inlineGlobalAliasIfPossible(name, ref, namespace)) {
name.removeRef(ref);
}
}
}
}
// Check if {@code name} has any aliases left after the
// local-alias-inlining above.
if ((name.type == Name.Type.OBJECTLIT || name.type == Name.Type.FUNCTION)
&& name.aliasingGets == 0
&& name.props != null) {
// All of {@code name}'s children meet condition (a), so they can be
// added to the worklist.
workList.addAll(name.props);
}
}
}
private boolean inlineAliasIfPossible(Name name, Ref alias, GlobalNamespace namespace) {
// Ensure that the alias is assigned to a local variable at that
// variable's declaration. If the alias's parent is a NAME,
// then the NAME must be the child of a VAR node, and we must
// be in a VAR assignment.
Node aliasParent = alias.node.getParent();
if (aliasParent.isName()) {
// Ensure that the local variable is well defined and never reassigned.
Scope scope = alias.scope;
String aliasVarName = aliasParent.getString();
Var aliasVar = scope.getVar(aliasVarName);
ReferenceCollectingCallback collector =
new ReferenceCollectingCallback(
compiler,
ReferenceCollectingCallback.DO_NOTHING_BEHAVIOR,
new Es6SyntacticScopeCreator(compiler),
Predicates.equalTo(aliasVar));
collector.processScope(scope);
ReferenceCollection aliasRefs = collector.getReferences(aliasVar);
Set newNodes = new LinkedHashSet<>();
if (aliasRefs.isWellDefined() && aliasRefs.firstReferenceIsAssigningDeclaration()) {
if (!aliasRefs.isAssignedOnceInLifetime()) {
// Static properties of constructors are always collapsed.
// So, if a constructor is aliased and its properties are accessed from
// the alias, we would like to inline the alias here to access the
// properties correctly.
// But if the aliased variable is assigned more than once, we can't
// inline, so we warn.
if (name.isConstructor()) {
boolean accessPropsAfterAliasing = false;
for (Reference ref : aliasRefs.references) {
if (ref.getNode().getParent().isGetProp()) {
accessPropsAfterAliasing = true;
break;
}
}
if (accessPropsAfterAliasing) {
compiler.report(JSError.make(aliasParent, UNSAFE_CTOR_ALIASING, aliasVarName));
}
}
return false;
}
// The alias is well-formed, so do the inlining now.
int size = aliasRefs.references.size();
for (int i = 1; i < size; i++) {
ReferenceCollectingCallback.Reference aliasRef = aliasRefs.references.get(i);
Node newNode = alias.node.cloneTree();
aliasRef.getParent().replaceChild(aliasRef.getNode(), newNode);
newNodes.add(new AstChange(getRefModule(aliasRef), aliasRef.getScope(), newNode));
}
// just set the original alias to null.
aliasParent.replaceChild(alias.node, IR.nullNode());
codeChanged = true;
compiler.reportChangeToEnclosingScope(aliasParent);
// Inlining the variable may have introduced new references
// to descendants of {@code name}. So those need to be collected now.
namespace.scanNewNodes(newNodes);
return true;
}
}
return false;
}
/**
* Attempt to inline an global alias of a global name. This requires that the name is well
* defined: assigned unconditionally, assigned exactly once. It is assumed that, the name for
* which it is an alias must already meet these same requirements.
*
* @param alias The alias to inline
* @return Whether the alias was inlined.
*/
private boolean inlineGlobalAliasIfPossible(Name name, Ref alias, GlobalNamespace namespace) {
// Ensure that the alias is assigned to global name at that the
// declaration.
Node aliasParent = alias.node.getParent();
if ((aliasParent.isAssign() || aliasParent.isName())
&& NodeUtil.isExecutedExactlyOnce(aliasParent)
// We special-case for constructors here, to inline constructor aliases
// more aggressively in global scope.
// We do this because constructor properties are always collapsed,
// so we want to inline the aliases also to avoid breakages.
// TODO(tbreisacher): Do we still need this special case?
|| aliasParent.isName() && name.isConstructor()) {
Node lvalue = aliasParent.isName() ? aliasParent : aliasParent.getFirstChild();
if (!lvalue.isQualifiedName()) {
return false;
}
if (lvalue.isName()
&& compiler.getCodingConvention().isExported(lvalue.getString(), /* local */ false)) {
return false;
}
name = namespace.getSlot(lvalue.getQualifiedName());
if (name != null && name.isInlinableGlobalAlias()) {
Set newNodes = new LinkedHashSet<>();
List refs = new ArrayList<>(name.getRefs());
for (Ref ref : refs) {
switch (ref.type) {
case SET_FROM_GLOBAL:
continue;
case DIRECT_GET:
case ALIASING_GET:
case PROTOTYPE_GET:
case CALL_GET:
Node newNode = alias.node.cloneTree();
Node node = ref.node;
node.getParent().replaceChild(node, newNode);
newNodes.add(new AstChange(ref.module, ref.scope, newNode));
name.removeRef(ref);
break;
default:
throw new IllegalStateException();
}
}
rewriteAliasProps(name, alias.node, 0, newNodes);
// just set the original alias to null.
aliasParent.replaceChild(alias.node, IR.nullNode());
codeChanged = true;
compiler.reportChangeToEnclosingScope(aliasParent);
// Inlining the variable may have introduced new references
// to descendants of {@code name}. So those need to be collected now.
namespace.scanNewNodes(newNodes);
return true;
}
}
return false;
}
}