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

[Cong Hou via llvm-commits]

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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