RFR: 8283187: C2: loop candidate for superword not always unrolled fully if superword fails [v2]

[Tobias Hartmann]

On Tue, 22 Mar 2022 12:18:22 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> IdealLoopTree::policy_unroll_slp_analysis() restricts unrolling of
>> loops that are found to be candidate for superword but if superword
>> then fails, unrolling doesn't always resume. SuperWord::output() has
>> logic for that in one of the failure paths but some other paths are
>> not covered (for instance in the case of the test case). I propose
>> that superword explictly returns whether it succeeded or not and that
>> in case of failure, for a main loop, unrolling be attempted again.
>
> Roland Westrelin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update test/hotspot/jtreg/compiler/c2/irTests/TestSuperwordFailsUnrolling.java
>   
>   Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>

I executed some testing and `compiler/c2/irTests/TestSuperwordFailsUnrolling.java` fails on Windows only with:

java.lang.Error: failed to install whitebox classes
	at compiler.lib.ir_framework.TestFramework.installWhiteBox(TestFramework.java:529)
	at compiler.lib.ir_framework.TestFramework.start(TestFramework.java:318)
	at compiler.lib.ir_framework.TestFramework.run(TestFramework.java:210)
	at compiler.lib.ir_framework.TestFramework.run(TestFramework.java:199)
	at compiler.c2.irTests.TestSuperwordFailsUnrolling.main(TestSuperwordFailsUnrolling.java:48)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104)
	at java.base/java.lang.reflect.Method.invoke(Method.java:577)
	at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:127)
	at java.base/java.lang.Thread.run(Thread.java:828)
Caused by: java.nio.file.FileSystemException: sun\\hotspot\\WhiteBox.class: The process cannot access the file because it is being used by another process
	at java.base/sun.nio.fs.WindowsException.translateToIOException(WindowsException.java:92)
	at java.base/sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:103)
	at java.base/sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:108)
	at java.base/sun.nio.fs.WindowsFileSystemProvider.implDelete(WindowsFileSystemProvider.java:275)
	at java.base/sun.nio.fs.AbstractFileSystemProvider.deleteIfExists(AbstractFileSystemProvider.java:110)
	at java.base/java.nio.file.Files.deleteIfExists(Files.java:1191)
	at java.base/java.nio.file.Files.copy(Files.java:3149)
	at jdk.test.lib.helpers.ClassFileInstaller.writeToDisk(ClassFileInstaller.java:296)
	at jdk.test.lib.helpers.ClassFileInstaller.writeClassToDisk(ClassFileInstaller.java:255)
	at jdk.test.lib.helpers.ClassFileInstaller.writeClassToDisk(ClassFileInstaller.java:237)
	at jdk.test.lib.helpers.ClassFileInstaller.writeClassToDisk(ClassFileInstaller.java:234)
	at jdk.test.lib.helpers.ClassFileInstaller.main(ClassFileInstaller.java:97)
	at compiler.lib.ir_framework.TestFramework.installWhiteBox(TestFramework.java:527)
	... 8 more



Weird but reproducible.

-------------

Changes requested by thartmann (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/7822