From: Jeff Law <law@redhat.com>
To: "rohitarulraj@freescale.com" <rohitarulraj@freescale.com>,
"gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>,
"rguenther@suse.de" <rguenther@suse.de>,
Jakub Jelinek <jakub@redhat.com>
Cc: Alan Modra <amodra@gmail.com>, David Edelsohn <dje.gcc@gmail.com>,
Edmar Wienskoski <edmar@freescale.com>
Subject: Re: [RFC: Patch, PR 60158] gcc/varasm.c : Pass actual alignment value to output_constant_pool_2
Date: Fri, 15 May 2015 05:01:00 -0000 [thread overview]
Message-ID: <55557D4C.9010500@redhat.com> (raw)
In-Reply-To: <BLUPR03MB1458C208112FCA605CF65F26C2D10@BLUPR03MB1458.namprd03.prod.outlook.com>
On 05/05/2015 01:59 AM, rohitarulraj@freescale.com wrote:
>>> Jeff, the issue is still reproducible with GCC v4.8 branch but
>>> not with GCC
>> v4.9 or trunk. Was it fixed by some other approach or has the bug
>> gone latent? Obviously if the former, then the patch is only
>> relevant to gcc-4.8 if the latter, then we'll still want to get it
>> fixed on the trunk and possibly in the release branches.
>>
>> Can you please investigate if the bug has been fixed by other means
>> or if it's just gone latent on the trunk?
>
> Jeff,
>
> 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
next prev parent reply other threads:[~2015-05-15 5:00 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-27 14:27 rohitarulraj
2015-04-28 10:06 ` rohitarulraj
2015-04-28 18:37 ` Jeff Law
2015-04-28 18:46 ` rohitarulraj
2015-04-28 22:46 ` Jeff Law
2015-04-29 10:43 ` rohitarulraj
2015-04-30 15:15 ` Jeff Law
2015-04-30 15:44 ` rohitarulraj
2015-04-30 15:55 ` Jeff Law
2015-05-05 7:59 ` rohitarulraj
2015-05-15 5:01 ` Jeff Law [this message]
2015-05-15 10:38 ` Dharmakan Rohit Arul Raj
2015-05-15 17:53 ` Jeff Law
2015-05-18 8:00 ` Richard Biener
2015-05-25 8:21 ` Dharmakan Rohit Arul Raj
2015-05-26 8:49 ` Richard Biener
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