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

[Tobias Hartmann]

On Tue, 15 Mar 2022 15:45:08 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.

Good catch! The fix looks good to me.

test/hotspot/jtreg/compiler/c2/irTests/TestSuperwordFailsUnrolling.java line 49:

> 47:         }
> 48:         TestFramework.run();
> 49: 

Suggestion:

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

Marked as reviewed by thartmann (Reviewer).

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