8334484: [lworld] new translation strategy for instance field initializers

Reviewed-by: mcimadamore

Author: Vicente Romero

src/jdk.compiler/share/classes/com/sun/tools/javac/code/Symbol.java

@@ -407,6 +407,10 @@ public boolean isStrict() {
         return (flags() & STRICT) != 0;
     }
 
+    public boolean isStrictInstance() {
+        return (flags() & STRICT) != 0 && (flags() & STATIC) == 0;
+    }
+
     public boolean hasStrict() {
         return (flags() & HAS_STRICT) != 0;
     }

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/CompileStates.java

@@ -63,7 +63,8 @@ public enum CompileState {
         TRANSPATTERNS(8),
         LOWER(9),
         UNLAMBDA(10),
-        GENERATE(11);
+        STRICT_FIELDS_PROXIES(11),
+        GENERATE(12);
 
         CompileState(int value) {
             this.value = value;

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/LocalProxyVarsGen.java

@@ -0,0 +1,266 @@
+/*
+ * Copyright (c) 2024, 2025, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package com.sun.tools.javac.comp;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.Set;
+
+import com.sun.tools.javac.code.Symbol;
+import com.sun.tools.javac.code.Symbol.ClassSymbol;
+import com.sun.tools.javac.code.Symbol.VarSymbol;
+import com.sun.tools.javac.code.Types;
+import com.sun.tools.javac.tree.JCTree.JCAssign;
+import com.sun.tools.javac.tree.JCTree.JCExpression;
+import com.sun.tools.javac.tree.JCTree.JCMethodDecl;
+import com.sun.tools.javac.tree.JCTree.JCVariableDecl;
+import com.sun.tools.javac.tree.TreeMaker;
+import com.sun.tools.javac.tree.TreeTranslator;
+import com.sun.tools.javac.util.Context;
+import com.sun.tools.javac.util.ListBuffer;
+import com.sun.tools.javac.util.Name;
+import com.sun.tools.javac.util.Names;
+
+import static com.sun.tools.javac.code.Flags.FINAL;
+import static com.sun.tools.javac.code.Flags.SYNTHETIC;
+import static com.sun.tools.javac.tree.JCTree.Tag.VARDEF;
+
+import com.sun.tools.javac.jvm.Target;
+import com.sun.tools.javac.tree.JCTree;
+import com.sun.tools.javac.tree.JCTree.JCClassDecl;
+import com.sun.tools.javac.tree.JCTree.JCStatement;
+import com.sun.tools.javac.tree.TreeInfo;
+import com.sun.tools.javac.util.List;
+import com.sun.tools.javac.util.Options;
+
+/** This phase adds local variable proxies for strict fields that are read during the
+ *  early construction phase (prologue)
+ *
+ *  Assignments to the affected instance fields will be rewritten as assignments to a
+ *  local proxy variable. Fields will be assigned to with its corresponding local variable
+ *  proxy just before the super invocation and after its arguments, if any, have been evaluated.
+ *
+ *  <p><b>This is NOT part of any supported API.
+ *  If you write code that depends on this, you do so at your own risk.
+ *  This code and its internal interfaces are subject to change or
+ *  deletion without notice.</b>
+ */
+public class LocalProxyVarsGen extends TreeTranslator {
+
+    protected static final Context.Key<LocalProxyVarsGen> valueInitializersKey = new Context.Key<>();
+
+    public static LocalProxyVarsGen instance(Context context) {
+        LocalProxyVarsGen instance = context.get(valueInitializersKey);
+        if (instance == null)
+            instance = new LocalProxyVarsGen(context);
+        return instance;
+    }
+
+    private final Types types;
+    private final Names names;
+    private final Target target;
+    private TreeMaker make;
+    private final UnsetFieldsInfo unsetFieldsInfo;
+    private ClassSymbol currentClass = null;
+    private java.util.List<JCVariableDecl> strictInstanceFields;
+    private Map<JCMethodDecl, Set<Symbol>> strictFieldsReadInPrologue = new HashMap<>();
+
+    private final boolean noLocalProxyVars;
+
+    @SuppressWarnings("this-escape")
+    protected LocalProxyVarsGen(Context context) {
+        context.put(valueInitializersKey, this);
+        make = TreeMaker.instance(context);
+        types = Types.instance(context);
+        names = Names.instance(context);
+        target = Target.instance(context);
+        unsetFieldsInfo = UnsetFieldsInfo.instance(context);
+        Options options = Options.instance(context);
+        noLocalProxyVars = options.isSet("noLocalProxyVars");
+    }
+
+    public void addStrictFieldReadInPrologue(JCMethodDecl constructor, Symbol sym) {
+        Set<Symbol> fieldSet = strictFieldsReadInPrologue.getOrDefault(constructor, new HashSet<>());
+        fieldSet.add(sym);
+        strictFieldsReadInPrologue.put(constructor, fieldSet);
+    }
+
+    public JCTree translateTopLevelClass(JCTree cdef, TreeMaker make) {
+        if (!noLocalProxyVars) {
+            try {
+                this.make = make;
+                return translate(cdef);
+            } finally {
+                // note that recursive invocations of this method fail hard
+                this.make = null;
+            }
+        } else {
+            return cdef;
+        }
+    }
+
+    @Override
+    public void visitClassDef(JCClassDecl tree) {
+        ClassSymbol prevCurrentClass = currentClass;
+        java.util.List<JCVariableDecl> prevStrictInstanceFields = strictInstanceFields;
+        try {
+            currentClass = tree.sym;
+            strictInstanceFields = tree.defs.stream()
+                    .filter(t -> t.hasTag(VARDEF))
+                    .map(t -> (JCVariableDecl)t)
+                    .filter(vd -> vd.sym.isStrict() && !vd.sym.isStatic())
+                    .collect(List.collector());
+            super.visitClassDef(tree);
+        } finally {
+            currentClass = prevCurrentClass;
+            strictInstanceFields = prevStrictInstanceFields;
+        }
+    }
+
+    public void visitMethodDef(JCMethodDecl tree) {
+        if (strictFieldsReadInPrologue.get(tree) != null) {
+            Set<Symbol> fieldSet = strictFieldsReadInPrologue.get(tree);
+            java.util.List<JCVariableDecl> strictFieldsRead = new ArrayList<>();
+            for (JCVariableDecl sfield : strictInstanceFields) {
+                if (fieldSet.contains(sfield.sym)) {
+                    strictFieldsRead.add(sfield);
+                }
+            }
+            addLocalProxiesFor(tree, strictFieldsRead);
+            strictFieldsReadInPrologue.remove(tree);
+        }
+        super.visitMethodDef(tree);
+    }
+
+    void addLocalProxiesFor(JCMethodDecl constructor, java.util.List<JCVariableDecl> multiAssignedStrictFields) {
+        ListBuffer<JCStatement> localDeclarations = new ListBuffer<>();
+        Map<Symbol, Symbol> fieldToLocalMap = new LinkedHashMap<>();
+
+        for (JCVariableDecl fieldDecl : multiAssignedStrictFields) {
+            long flags = SYNTHETIC;
+            VarSymbol proxy = new VarSymbol(flags, newLocalName(fieldDecl.name.toString()), fieldDecl.sym.erasure(types), constructor.sym);
+            fieldToLocalMap.put(fieldDecl.sym, proxy);
+            JCVariableDecl localDecl = make.at(constructor.pos).VarDef(proxy, fieldDecl.init);
+            localDecl.vartype = fieldDecl.vartype;
+            localDeclarations = localDeclarations.append(localDecl);
+        }
+
+        FieldRewriter fieldRewriter = new FieldRewriter(constructor, fieldToLocalMap);
+        ListBuffer<JCStatement> newBody = new ListBuffer<>();
+        for (JCStatement st : constructor.body.stats) {
+            newBody = newBody.append(fieldRewriter.translate(st));
+        }
+        localDeclarations.addAll(newBody);
+        ListBuffer<JCStatement> assigmentsBeforeSuper = new ListBuffer<>();
+        for (Symbol vsym : fieldToLocalMap.keySet()) {
+            Symbol local = fieldToLocalMap.get(vsym);
+            assigmentsBeforeSuper.append(make.at(constructor.pos()).Assignment(vsym, make.at(constructor.pos()).Ident(local)));
+        }
+        constructor.body.stats = localDeclarations.toList();
+        JCTree.JCMethodInvocation constructorCall = TreeInfo.findConstructorCall(constructor);
+        if (constructorCall.args.isEmpty()) {
+            // this is just a super invocation with no arguments we can set the fields just before the invocation
+            // and let Gen do the rest
+            TreeInfo.mapSuperCalls(constructor.body, supercall -> make.Block(0, assigmentsBeforeSuper.toList().append(supercall)));
+        } else {
+            // we need to generate fresh local variables to catch the values of the arguments, then
+            // assign the proxy locals to the fields and finally invoke the super with the fresh local variables
+            int argPosition = 0;
+            ListBuffer<JCStatement> superArgsProxies = new ListBuffer<>();
+            for (JCExpression arg : constructorCall.args) {
+                long flags = SYNTHETIC | FINAL;
+                VarSymbol proxyForArgSym = new VarSymbol(flags, newLocalName("" + argPosition), types.erasure(arg.type), constructor.sym);
+                JCVariableDecl proxyForArgDecl = make.at(constructor.pos).VarDef(proxyForArgSym, arg);
+                superArgsProxies = superArgsProxies.append(proxyForArgDecl);
+                argPosition++;
+            }
+            List<JCStatement> superArgsProxiesList = superArgsProxies.toList();
+            ListBuffer<JCExpression> newArgs = new ListBuffer<>();
+            for (JCStatement argProxy : superArgsProxies) {
+                newArgs.add(make.at(argProxy.pos).Ident((JCVariableDecl) argProxy));
+            }
+            constructorCall.args = newArgs.toList();
+            TreeInfo.mapSuperCalls(constructor.body,
+                    supercall -> make.Block(0, superArgsProxiesList.appendList(assigmentsBeforeSuper.toList()).append(supercall)));
+        }
+    }
+
+    Name newLocalName(String name) {
+        return names.fromString("local" + target.syntheticNameChar() + name);
+    }
+
+    class FieldRewriter extends TreeTranslator {
+        JCMethodDecl md;
+        Map<Symbol, Symbol> fieldToLocalMap;
+        boolean ctorPrologue = true;
+
+        public FieldRewriter(JCMethodDecl md, Map<Symbol, Symbol> fieldToLocalMap) {
+            this.md = md;
+            this.fieldToLocalMap = fieldToLocalMap;
+        }
+
+        @Override
+        public void visitIdent(JCTree.JCIdent tree) {
+            if (ctorPrologue && fieldToLocalMap.get(tree.sym) != null) {
+                result = make.at(md).Ident(fieldToLocalMap.get(tree.sym));
+            } else {
+                result = tree;
+            }
+        }
+
+        @Override
+        public void visitSelect(JCTree.JCFieldAccess tree) {
+            super.visitSelect(tree);
+            if (ctorPrologue && fieldToLocalMap.get(tree.sym) != null) {
+                result = make.at(md).Ident(fieldToLocalMap.get(tree.sym));
+            } else {
+                result = tree;
+            }
+        }
+
+        @Override
+        public void visitAssign(JCAssign tree) {
+            JCExpression previousLHS = tree.lhs;
+            super.visitAssign(tree);
+            if (ctorPrologue && previousLHS != tree.lhs) {
+                unsetFieldsInfo.removeUnsetFieldInfo(currentClass, tree);
+            }
+        }
+
+        @Override
+        public void visitApply(JCTree.JCMethodInvocation tree) {
+            Name methName = TreeInfo.name(tree.meth);
+            boolean isConstructorCall = methName == names._this || methName == names._super;
+            super.visitApply(tree);
+            if (isConstructorCall) {
+                ctorPrologue = false;
+            }
+        }
+    }
+}

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Resolve.java

@@ -115,6 +115,7 @@ public class Resolve {
     final EnumSet<VerboseResolutionMode> verboseResolutionMode;
     final boolean dumpMethodReferenceSearchResults;
     final boolean dumpStacktraceOnError;
+    private final LocalProxyVarsGen localProxyVarsGen;
 
     WriteableScope polymorphicSignatureScope;
 
@@ -154,6 +155,7 @@ protected Resolve(Context context) {
         allowRecords = Feature.RECORDS.allowedInSource(source);
         dumpMethodReferenceSearchResults = options.isSet("debug.dumpMethodReferenceSearchResults");
         dumpStacktraceOnError = options.isSet("dev") || options.isSet(DOE);
+        localProxyVarsGen = LocalProxyVarsGen.instance(context);
     }
 
     /** error symbols, which are returned when resolution fails
@@ -1537,7 +1539,12 @@ Symbol findVar(DiagnosticPosition pos, Env<AttrContext> env, Name name) {
                         return new StaticError(sym);
                     if (env1.info.ctorPrologue && !isAllowedEarlyReference(pos, env1, (VarSymbol)sym)) {
                         if (!env.tree.hasTag(ASSIGN) || !TreeInfo.isIdentOrThisDotIdent(((JCAssign)env.tree).lhs)) {
-                            return new RefBeforeCtorCalledError(sym);
+                            if (!sym.isStrictInstance()) {
+                                return new RefBeforeCtorCalledError(sym);
+                            } else {
+                                localProxyVarsGen.addStrictFieldReadInPrologue(env.enclMethod, sym);
+                                return sym;
+                            }
                         }
                     }
                 }

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/UnsetFieldsInfo.java

@@ -88,4 +88,11 @@ public Set<VarSymbol> getUnsetFields(ClassSymbol csym, JCTree tree) {
         }
         return null;
     }
+
+    public void removeUnsetFieldInfo(ClassSymbol csym, JCTree tree) {
+        Map<JCTree, Set<VarSymbol>> treeToFieldsMap = unsetFieldsMap.get(csym);
+        if (treeToFieldsMap != null) {
+            treeToFieldsMap.remove(tree);
+        }
+    }
 }

src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/Code.java

@@ -190,6 +190,8 @@ public boolean checkLimits(DiagnosticPosition pos, Log log) {
 
     private Map<Integer, Set<VarSymbol>> cpToUnsetFieldsMap = new HashMap<>();
 
+    public Set<VarSymbol> initialUnsetFields;
+
     public Set<VarSymbol> currentUnsetFields;
 
     boolean generateAssertUnsetFieldsFrame;
@@ -1355,7 +1357,7 @@ void emitStackMapFrame(int pc, int localsSize) {
         }
 
         Set<VarSymbol> unsetFieldsAtPC = cpToUnsetFieldsMap.get(pc);
-        boolean generateAssertUnsetFieldsEntry = unsetFieldsAtPC != null && generateAssertUnsetFieldsFrame;
+        boolean generateAssertUnsetFieldsEntry = unsetFieldsAtPC != null && generateAssertUnsetFieldsFrame && !lastFrame.unsetFields.equals(unsetFieldsAtPC) ;
 
         if (stackMapTableBuffer == null) {
             stackMapTableBuffer = new StackMapTableEntry[20];
@@ -1366,10 +1368,10 @@ void emitStackMapFrame(int pc, int localsSize) {
         }
 
         if (generateAssertUnsetFieldsEntry) {
-            if (lastFrame.unsetFields == null || !lastFrame.unsetFields.equals(unsetFieldsAtPC)) {
-                stackMapTableBuffer[stackMapBufferSize++] = new StackMapTableEntry.AssertUnsetFields(pc, unsetFieldsAtPC);
-                frame.unsetFields = unsetFieldsAtPC;
-            }
+            stackMapTableBuffer[stackMapBufferSize++] = new StackMapTableEntry.AssertUnsetFields(pc, unsetFieldsAtPC);
+            frame.unsetFields = unsetFieldsAtPC;
+        } else {
+            frame.unsetFields = lastFrame.unsetFields;
         }
         stackMapTableBuffer[stackMapBufferSize++] =
                 StackMapTableEntry.getInstance(frame, lastFrame, types, pc);
@@ -1403,6 +1405,7 @@ StackMapFrame getInitialFrame() {
         }
         frame.pc = -1;
         frame.stack = null;
+        frame.unsetFields = initialUnsetFields;
         return frame;
     }
 

src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/Gen.java

@@ -586,11 +586,11 @@ void rewriteInitializersIfNeeded(JCMethodDecl md, List<JCStatement> initCode) {
         }
     }
 
-    class InitializerVisitor extends TreeScanner {
+    public static class InitializerVisitor extends TreeScanner {
         JCMethodDecl md;
         Set<JCExpression> exprSet;
 
-        InitializerVisitor(JCMethodDecl md, Set<JCExpression> exprSet) {
+        public InitializerVisitor(JCMethodDecl md, Set<JCExpression> exprSet) {
             this.md = md;
             this.exprSet = exprSet;
         }
@@ -998,6 +998,7 @@ else if (tree.body != null) {
                 Set<VarSymbol> prevUnsetFields = code.currentUnsetFields;
                 if (meth.isConstructor()) {
                     code.currentUnsetFields = unsetFieldsInfo.getUnsetFields(env.enclClass.sym, tree.body);
+                    code.initialUnsetFields = unsetFieldsInfo.getUnsetFields(env.enclClass.sym, tree.body);
                 }
 
                 try {