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Re: [PATCH PR68021]Set ratio to 1 when computing the value of biv cand by itself
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Bin Cheng <Bin dot Cheng at arm dot com>
- Cc: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, nd <nd at arm dot com>
- Date: Wed, 10 Feb 2016 14:27:01 +0100
- Subject: Re: [PATCH PR68021]Set ratio to 1 when computing the value of biv cand by itself
- Authentication-results: sourceware.org; auth=none
- References: <HE1PR08MB0507FEFCF4FF37E4E98CCDBFE7D70 at HE1PR08MB0507 dot eurprd08 dot prod dot outlook dot com>
On Wed, Feb 10, 2016 at 12:34 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
> Hi,
> This is another way to fix PR68021, and I think it's the least intrusive way. The issue is triggered in a special case in which cand is a original biv, and use denotes the value of the biv itself. In this case, the use is added specifically for the original biv, as a result, get_computation_aff isn't called for the <cand, use> pair before rewriting the use. It is possible that constant_multiple_of/operand_equal_q could fail because of inconsistent fold behavior. The fold behavior is fully described in PR68021.
> This patch fixes IVOPT part of issue by setting ratio to 1, because it is known that the use has the value of the biv cand.
>
> Bootstrap and test on x86_64 and aarch64. Is it OK if no failures?
Ok, but please add a comment why we have this special-casing instead
of relying on constant_multiple_of.
Thanks,
Richard.
> Thanks,
> bin
>
> 2016-02-09 Bin Cheng <bin.cheng@arm.com>
>
> PR tree-optimization/68021
> * tree-ssa-loop-ivopts.c (get_computation_aff): Set ratio to 1 if
> when computing the value of biv cand by itself.
>
> gcc/testsuite/ChangeLog
> 2016-02-09 Bin Cheng <bin.cheng@arm.com>
>
> PR tree-optimization/68021
> * gcc.dg/tree-ssa/pr68021.c: New test.