8295020: javac emits incorrect code for for-each on an intersection type.

[sadayapalam]

Eliminate needless casts and ensure invoked method is looked up against the appropriate receiver type

---

Progress

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Issue

• JDK-8295020: javac emits incorrect code for for-each on an intersection type.

Reviewers

• Maurizio Cimadamore (@mcimadamore - Reviewer)

Reviewing

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[bridgekeeper[bot]]

:wave: Welcome back sadayapalam! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[sadayapalam]

Notes for the reviewer:

The loop from the test case viz:

for (Object s : (MyIterable & Serializable) null) {}

gets transformed by Lower into:

for (Iterator i$ = ((Iterable)(Main$MyIterable & Serializable)null).iterator(); i$.hasNext(); ) {
    Object s = (Object)i$.next();
    {
    }
}

This transformation is problematic in a couple of ways:

The cast of the expression (Main$MyIterable & Serializable)null into (Iterable) is not
required at all. After erasure the type of the intersection cast node is actually
Main$MyIterable which is already an Iterable. As a matter of Gen#visitTypeCast correctly
deduces this to be a redundant cast and does not emit a checkcast in the class file.

The iterator() method to be invoked is looked up against the JCEnhancedForLoop#expr.type
i.e from Main$MyIterable while the type of the receiver expression for the iterator()
method invocation is the casted type of (Iterable)(Main$MyIterable & Serializable)null).
As a result, the method
com.sun.tools.javac.jvm.Gen#binaryQualifier((Symbol sym, Type site)
attempts to coalesce the method iterator() (sym) as owned by Iterator (site) by calling
com.sun.tools.javac.code.Symbol.MethodSymbol#clone which simply changes ownership of
the method symbol iterator() without accommodating for descriptor difference that arises
due to covariant return type.

The fix comes in two parts: (a) Ensuring that a cast is inserted only when absolutely necessary and not just because JCEnhancedForLoop#expr.type happens to be an intersection type (b) Ensuring that where a type cast is inserted, the iterator() method is looked up against the modified receiver type.

(An open question is whether MethodSymbol#clone should be fixed to not just rewire ownership, but also account for differences in descriptor - if deemed needed this can be followed up in a separate ticket.)

[openjdk[bot]]

@sadayapalam The following label will be automatically applied to this pull request:

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[mlbridge[bot]]

Webrevs

• 02: Full - Incremental (f3319aa8)
• 01: Full - Incremental (2ee16e16)
• 00: Full (ea162848)

[openjdk[bot]]

@sadayapalam This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8295020: javac emits incorrect code for for-each on an intersection type.

Reviewed-by: mcimadamore

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 1 new commit pushed to the master branch:

• 74a51ccc86525eb4b1eb2e5cb11e605ca9e9fc5d: 8292698: Improve performance of DataInputStream

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch. As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[sadayapalam]

/integrate

[openjdk[bot]]

Going to push as commit cf07eaeb9291da725181832b8bb1dc54957ba886. Since your change was applied there have been 3 commits pushed to the master branch:

• b3bb3e6ed89f3abcaae584fcbe75688141e886cb: 8295325: tools/jlink/plugins/SaveJlinkArgfilesPluginTest.java fails on Linux ppc64le
• 9005af3b90fbd3607aeb83efe1c4a6ffa5d104f0: 8295110: RISC-V: Mark out relocations as incompressible
• 74a51ccc86525eb4b1eb2e5cb11e605ca9e9fc5d: 8292698: Improve performance of DataInputStream

Your commit was automatically rebased without conflicts.

[openjdk[bot]]

@sadayapalam Pushed as commit cf07eaeb9291da725181832b8bb1dc54957ba886.

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