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Re: [PATCH 1/3]Improve induction variable elimination
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Bin Cheng <bin dot cheng at arm dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Fri, 25 Jul 2014 14:27:35 +0200
- Subject: Re: [PATCH 1/3]Improve induction variable elimination
- Authentication-results: sourceware.org; auth=none
- References: <002a01cfa19e$8752d0d0$95f87270$ at arm dot com>
On Thu, Jul 17, 2014 at 11:07 AM, Bin Cheng <bin.cheng@arm.com> wrote:
> Hi,
> This is a series of three patches improving induction variable elimination.
> Currently GCC only eliminates iv for very specific case when the loopâs
> latch could run zero times, i.e., when may_be_zero field of loop niter
> information evaluates to true. In fact, itâs so specific that
> iv_elimination_compare_lt rarely succeeds during either GCC bootstrap or
> spec2000/spec2006 compilation. Though intrusive data shows these patches
> donât help iv elimination that much for GCC bootstrap, they do capture
> 5%~15% more eliminations for compiling spec2000/2006. Detailed numbers are
> like:
> 2k/int 2k/fp 2k6/int 2k6/fp
> improve ~9.6% ~4.8% ~5.5% ~14.4%
>
> All patches pass bootstrap and regression test on x86_64/x86. I will
> bootstrap and test them on aarch64/arm platforms too.
>
> The first patch turns to tree operand_equal_p to check the number of
> iterations in iv_elimination_lt. Though I think this change isnât necessary
> for current code, itâs needed if we further relax iv elimination for cases
> in which sign/unsigned conversion is involved.
As said elsewhere this bug should be fixed in tree-affine.c. Do you have
a testcase?
Thanks,
Richard.
> Thanks,
> bin
>
> 2014-07-17 Bin Cheng <bin.cheng@arm.com>
>
> * tree-ssa-loop-ivopts.c (iv_elimination_compare_lt): Check number
> of iteration using tree comparison.