Integrated: 8273277: C2: Move conditional negation into rc_predicate

[Nils Eliasson]

On Mon, 18 Oct 2021 13:24:19 GMT, Nils Eliasson <neliasso at openjdk.org> wrote:

> Hi,
> 
> I need some feedback on this patch. This was reported from Tencent and found in internal testing about the same time. This patch is based on a a patch provided by Tencent.
> 
> In some very specific circumstances we need to negate the range checks that we create in PhaseIdealLoop::loop_predication_impl_helper. This is done in three places, but that method also calls insert_initial_skeleton_predicate where this isn't taken into account. 
> 
> To simplify things I have moved the negation logic into rc_predicate. This should prevent us from missing this check again.
> 
> I do have a concern that negating the condition of the rangecheck in the skeleton predicate, since the skeleton predicate will be used as a clone template, and some rangechecks optimizations seems to assume that range checks always have LT as the condidtion. On the other hand - it is a really uncommon scenario since we haven't failed here before.
> 
> Feedback appreciated.
> 
> Best regards,
> Nils

This pull request has now been integrated.

Changeset: 710f4964
Author:    Nils Eliasson <neliasso at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/710f496456d642c3e98d230270598f0b2dc75aba
Stats:     96 lines in 5 files changed: 71 ins; 12 del; 13 mod

8273277: C2: Move conditional negation into rc_predicate

Reviewed-by: thartmann, chagedorn, kvn

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

PR: https://git.openjdk.java.net/jdk/pull/5987