[llvm] r227983 - Fix program crashes due to alignment exceptions generated for SSE memop instructions (PR22371).

[Craig Topper]

I thought we had converted all of AVX/AVX2 to use 'loadXXX' instead of
'memopXXX'?

On Wed, Feb 4, 2015 at 11:44 PM, Demikhovsky, Elena <
elena.demikhovsky at intel.com> wrote:

> Hi,
> You removed FeatureVectorUAMem form HSW, but you did not add
> FeatureSSEUnalignedMem
>                                       FeatureAVX2,
>                                       FeatureCMPXCHG16B,
>                                       FeatureFastUAMem,
> -                                     FeatureVectorUAMem,
>                                       FeaturePOPCNT,
>                                       FeatureAES,
>                                       FeaturePCLMUL,
>
> How memop should work now on AVX/AVX2? Will it require alignment now?
>
> def memop : PatFrag<(ops node:$ptr), (load node:$ptr), [{
> -  return    Subtarget->hasVectorUAMem()
> +  return    Subtarget->hasSSEUnalignedMem()
>           || cast<LoadSDNode>(N)->getAlignment() >= 16;
>  }]>;
>
> -  Elena
>
>
> -----Original Message-----
> From: Kuperstein, Michael M
> Sent: Wednesday, February 04, 2015 21:41
> To: Hans Wennborg; Nadav Rotem; Demikhovsky, Elena
> Cc: Sanjay Patel; llvm-commits
> Subject: RE: [llvm] r227983 - Fix program crashes due to alignment
> exceptions generated for SSE memop instructions (PR22371).
>
> I understand this on roughly the same level as Nadav does (looks correct,
> and should be safer than the current situation), but Elena should be able
> to give an authoritative answer.
> Elena, could you comment?
>
> Michael
>
> -----Original Message-----
> From: hwennborg at google.com [mailto:hwennborg at google.com] On Behalf Of
> Hans Wennborg
> Sent: Wednesday, February 04, 2015 20:53
> To: Nadav Rotem
> Cc: Sanjay Patel; llvm-commits; Demikhovsky, Elena; Kuperstein, Michael M
> Subject: Re: [llvm] r227983 - Fix program crashes due to alignment
> exceptions generated for SSE memop instructions (PR22371).
>
> Elena, Michael: is this safe for merging to 3.6?
>
> As far as I understand it's basically a revert or r224330.
>
> On Tue, Feb 3, 2015 at 3:44 PM, Nadav Rotem <nrotem at apple.com> wrote:
> > The change looks good to me, but I would wait a day and let Elena or
> > Michael review it.
> >
> > On Feb 3, 2015, at 3:19 PM, Hans Wennborg <hans at chromium.org> wrote:
> >
> > On Tue, Feb 3, 2015 at 9:13 AM, Sanjay Patel <spatel at rotateright.com>
> wrote:
> >
> > Author: spatel
> > Date: Tue Feb  3 11:13:04 2015
> > New Revision: 227983
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=227983&view=rev
> > Log:
> > Fix program crashes due to alignment exceptions generated for SSE
> > memop instructions (PR22371).
> >
> > r224330 introduced a bug by misinterpreting the "FeatureVectorUAMem" bit.
> > The commit log says that change did not affect anything, but that's
> > not correct.
> > That change allowed SSE instructions to have unaligned mem operands
> > folded into math ops, and that's not allowed in the default
> > specification for any SSE variant.
> >
> > The bug is exposed when compiling for an AVX-capable CPU that had this
> > feature flag but without enabling AVX codegen. Another mistake in
> > r224330 was not adding the feature flag to all AVX CPUs; the AMD chips
> > were excluded.
> >
> > This is part of the fix for PR22371 (
> > http://llvm.org/bugs/show_bug.cgi?id=22371 ).
> >
> > This feature bit is SSE-specific, so I've renamed it to
> > "FeatureSSEUnalignedMem".
> > Changed the existing test case for the feature bit to reflect the new
> > name and renamed the test file itself to better reflect the feature.
> > Added runs to fold-vex.ll to check for the failing codegen.
> >
> > Note that the feature bit is not set by default on any CPU because it
> > may require a configuration register setting to enable the enhanced
> > unaligned behavior.
> >
> >
> > Sanjay requested in [1] that we should merge this to the 3.6 branch.
> > I'm not qualified to determine if this is safe or not. Is there somone
> > else with X86 expertise that would like to chime in? Nadav, you're
> > listed as the code owner here.
> >
> > Thanks,
> > Hans
> >
> > 1. http://llvm.org/bugs/show_bug.cgi?id=22374#c3
> >
> >
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-- 
~Craig
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