Re: [PATCH 0/2][IRA,LRA] Fix PR86939, IRA incorrectly creates an interference between a pseudo register and a hard register

[Peter Bergner <bergner at linux dot ibm dot com>]

On 9/28/18 4:34 PM, Vladimir Makarov wrote:
> I remember I experimented with value numbering and using it in building
> conflicts (that time it was global.c) but it did not improve the code as
> I expected and made RA much slower.

Yes, value numbering is not cheap to compute for catching special cases 
like this that probably don't happen too often.  Handling copies is fairly
cheap and easy though.


> We had some PRs with old RA code generation in case of using undefined values.
> I don't remember what problems were exactly but I remember Ken Zadeck worked
> on this too.  That is why I probably chose the current scheme of conflict
> building.
> 
> May be I was wrong because you testing shows that it is not a problem anymore.

Maybe it was due to code relying on undefined behavior?  Anyway, it'll be good
to let PATCH 1 bake on trunk for a little while before we commit PATCH 2 to
catch any (if they exist) problems related to that change.


> The 1st patch is ok for me.  You can commit it to the trunk.

Ok, PATCH 1 is now committed, thanks!


> I'll review the second patch on the next week.

Sounds great as it gives any problems caused or exposed by PATCH 1 time to
be reported.  Thanks again!


Peter