[llvm] r255691 - [LoopVectorizer] Refine loop vectorizer's register usage calculator by ignoring specific instructions.

[Cong Hou via llvm-commits]

I just came back from China. I was sick on the last two days in the last
week and could not access any google sites at home. Thanks for reverting
it, Hans. I will keep looking into this patch.


thanks,
Cong

On Fri, Feb 19, 2016 at 1:47 PM, Hans Wennborg <hans at chromium.org> wrote:

> I've reverted this commit in r261368 and merged that to 3.8 in r261369
> to unbreak things in the meantime.
>
> On Wed, Feb 17, 2016 at 6:48 PM, Cong Hou <congh at google.com> wrote:
> > Sorry for the late reply! I am currently working in Beijing. Start
> > investigating it now...
> >
> >
> > thanks,
> > Cong
> >
> > On Wed, Feb 17, 2016 at 10:08 AM, Hans Wennborg <hans at chromium.org>
> wrote:
> >>
> >> On Tue, Feb 16, 2016 at 11:06 AM, Hans Wennborg <hans at chromium.org>
> wrote:
> >> > On Mon, Feb 15, 2016 at 12:28 PM, Dimitry Andric <dimitry at andric.com>
> >> > wrote:
> >> >> On 15 Dec 2015, at 23:45, Cong Hou via llvm-commits
> >> >> <llvm-commits at lists.llvm.org> wrote:
> >> >>>
> >> >>> Author: conghou
> >> >>> Date: Tue Dec 15 16:45:09 2015
> >> >>> New Revision: 255691
> >> >>>
> >> >>> URL: http://llvm.org/viewvc/llvm-project?rev=255691&view=rev
> >> >>> Log:
> >> >>> [LoopVectorizer] Refine loop vectorizer's register usage calculator
> by
> >> >>> ignoring specific instructions.
> >> >>>
> >> >>> (This is the third attempt to check in this patch, and the first two
> >> >>> are r255454
> >> >>> and r255460. The once failed test file reg-usage.ll is now moved to
> >> >>> test/Transform/LoopVectorize/X86 directory with target datalayout
> and
> >> >>> target
> >> >>> triple indicated.)
> >> >>>
> >> >>> LoopVectorizationCostModel::calculateRegisterUsage() is used to
> >> >>> estimate the
> >> >>> register usage for specific VFs. However, it takes into account many
> >> >>> instructions that won't be vectorized, such as induction variables,
> >> >>> GetElementPtr instruction, etc.. This makes the loop vectorizer too
> >> >>> conservative
> >> >>> when choosing VF. In this patch, the induction variables that won't
> be
> >> >>> vectorized plus GetElementPtr instruction will be added to
> >> >>> ValuesToIgnore set
> >> >>> so that their register usage won't be considered any more.
> >> >>>
> >> >>>
> >> >>> Differential revision: http://reviews.llvm.org/D15177
> >> >>
> >> >> This appears to have introduced a use-after-free, see
> >> >> https://llvm.org/bugs/show_bug.cgi?id=26509 for the details and a
> valgrind
> >> >> log.  Is there any way we can fix this one before 3.8 release, or
> revert it
> >> >> otherwise?
> >> >
> >> > Cong, do you think this is something that's easy to fix or should we
> >> > revert in the branch to be safe?
> >>
> >> Cong: ping?
> >
> >
>
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