[lworld] RFR: 8359370: [lworld] allow instance fields of identity classes to be readable in the prologue phase [v21]

[Maurizio Cimadamore]

On Mon, 1 Sep 2025 22:01:49 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 refactoring

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java line 1387:

> 1385:         void analyzeSymbol(JCTree tree) {
> 1386:             Symbol sym = TreeInfo.symbolFor(tree);
> 1387:             if (isInLHS && !insideLambdaOrClassDef) {

Question: for stuff that is NOT in LHS -- shouldn't we check that preview features are enabled? E.g. we don't want to allow reads in prologue unless `--enable-preview` is present, right?

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java line 1465:

> 1463:                     sym.isMemberOf(env.enclClass.sym, types)) {
> 1464:                 // Allow "Foo.this.x" when "Foo" is (also) an outer class, as this refers to the outer instance
> 1465:                 if (base != null) {

(optional) style only -- instead of setting `base` and then checking `base != null`, we could just rewrite the `if` as `if (tree.hasTag(SELECT))` ?

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1523#discussion_r2318981814
PR Review Comment: https://git.openjdk.org/valhalla/pull/1523#discussion_r2318977499