[lworld] RFR: 8359370: [lworld] allow instance fields of identity classes to be readable in the prologue phase [v13]

[Maurizio Cimadamore]

On Thu, 28 Aug 2025 12:55:05 GMT, Vicente Romero <vromero at openjdk.org> wrote:

>> Before this fix only strict fields were readable in the prologue phase. The proposed fix should allow any instance fields of identity classes to be readable in the prologue phase. This implies changes in flow analysis as before we were only tracking final and strict fields. There is also some "cooperation" needed in the code to detect cases when reading a field is not allowed in the prologue phase. For example some methods in Resolve don't have all the needed information at the moment they are dealing with some ASTs and part of the processing needs to be done in Attr
>> 
>> TIA
>> 
>> This PR is a remake of https://github.com/openjdk/valhalla/pull/1490
>
> Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:
> 
>   minor diff

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java line 1309:

> 1307:                 Symbol sym = symAndTree.symbol();
> 1308:                 JCTree tree = TreeInfo.skipParens(symAndTree.tree());
> 1309:                 if (sym.kind == VAR &&

Why doesn't this call analyze symbol?

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java line 1420:

> 1418:             Symbol sym = TreeInfo.symbolFor(tree);
> 1419:             if (sym != null) {
> 1420:                 if (!sym.isStatic() && !isMethodArgument(tree)) {

if you have a `sym`, in order to understand if something is a method parameter (not argument?) don't you need to check if `sym.owner == MTH` ?

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java line 1423:

> 1421:                     if (sym.name == names._this || sym.name == names._super) {
> 1422:                         // are we seeing something like `this` or `CurrentClass.this` or `SuperClass.super::foo`?
> 1423:                         if (TreeInfo.isExplicitThisReference(

Do we always report an error when seeing `Foo.this` ? What if we're not inside the prologue of `Foo` ?

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java line 1564:

> 1562:                         if (v.owner.kind == TYP && !v.isStatic() && v.isStrict()) {
> 1563:                             // strict field initializers are inlined in constructor's prologues
> 1564:                             CtorPrologueVisitor ctorPrologueVisitor = new CtorPrologueVisitor(initEnv);

Nice reuse

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1523#discussion_r2307950873
PR Review Comment: https://git.openjdk.org/valhalla/pull/1523#discussion_r2307957523
PR Review Comment: https://git.openjdk.org/valhalla/pull/1523#discussion_r2307959699
PR Review Comment: https://git.openjdk.org/valhalla/pull/1523#discussion_r2307961723