RE: [RFC: Patch, PR 60158] gcc/varasm.c : Pass actual alignment value to output_constant_pool_2

[Dharmakan Rohit Arul Raj <rohitarulraj@freescale.com>]

> -----Original Message-----
> From: Richard Biener [mailto:rguenther@suse.de]
> Sent: Monday, May 18, 2015 1:06 PM
> To: Jeff Law
> Cc: Dharmakan Rohit-B30502; gcc-patches@gcc.gnu.org; Jakub Jelinek; Alan
> Modra; David Edelsohn; Wienskoski Edmar-RA8797
> Subject: Re: [RFC: Patch, PR 60158] gcc/varasm.c : Pass actual alignment value
> to output_constant_pool_2
> 
> On Fri, 15 May 2015, Jeff Law wrote:
> 
> > On 05/15/2015 04:37 AM, Dharmakan Rohit Arul Raj wrote:
> > >
> > > > -----Original Message-----
> > > > From: Jeff Law [mailto:law@redhat.com]
> > > > Sent: Friday, May 15, 2015 10:30 AM
> > > > > Just to summarize: By default in GCC v4.7.x, all the constants
> > > > > are put into '.rodata.str1.4' section. In GCC v4.8.x from
> > > > > r192719 onwards, one of the move instruction of the string
> > > > > constant ".LC0" is getting spilled. The reload pass, for any
> > > > > constants that aren't allowed and can't be reloaded in to
> > > > > registers tries to change them into memory references. Then
> > > > > while emitting that string constant to asm code
> > > > > (A:varasm.c: output_constant_pool_1), it explicitly passes the
> > > > > alignment as 1 which prevents the generation of fix-up table
> > > > > entries in  'B: rs6000.c:rs6000_assemble_integer' because the
> > > > > data is considered unaligned now.
> > > > >
> > > > > The bug seems to have gone latent with an unrelated trunk commit
> > > > > r204695 [* tree-ssa-loop-ivopts.c (force_expr_to_var_cost):
> > > > > Refactor the code. Handle type conversion.]. This commit chooses
> > > > > different spill candidates hence all the string constants are
> > > > > being put in to '.rodata.str1.4´section.
> > > > >
> > > > > The check I had in the test case is that if there is a
> > > > > '.data.rel.ro.local', then there should be '.fixup' section generated.
> > > > >
> > > > > Please let me know if you need any other details.
> > > > Thanks.  Even though I wasn't able to trigger the bug with the
> > > > testcase from 65018, I went ahead and committed this patch to the
> > > > trunk.  It can't hurt and it's the right thing to do.
> > > >
> > > > Thanks for your patience,
> > > >
> > >
> > > Jeff, Thanks for checking-in the changes.
> > > Can we apply the patch to GCC v4.8 and GCC v4.9 branch as well?
> > That's up to the branch maintainers.  I'd think it's safe, but it's
> > ultimately their call.
> 
> If it's a regression or a wrong-code issue then it's ok to backport given the
> patch is safe, of course.

Just to confirm, can we backport the patch to GCC v4.8 & GCC v4.9 branch?

Regards,
Rohit