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Thanks Bradley.<br>
<br>
I see that the features set in <i>ARM.td</i> get written to the
generated file <i><build>/llvm/lib/Target/ARM/ARMGenSubtargetInfo.inc.</i>
Here the ProcA9 features appear in <i>ARMFeatureKV</i> table:<br>
<br>
<i>{ "a9", "Cortex-A9 ARM processors", { ARM::ProcA9 }, { <b>ARM::FeatureFP16</b>
} },<br>
<br>
</i>With your change, the features for ProcA9 in the above entry are
empty.<i> </i>This ARMFeatureKV table is then read in
MC/MCSubtargetInfo.cpp in the getFeatures() function.<br>
<br>
Thanks,<br>
Mandeep<br>
<br>
<div class="moz-cite-prefix">On 2/24/2016 2:42 AM, Bradley Smith
wrote:<br>
</div>
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The
idea behind that change was to make ARM.td clearer, that is,
adding architecture features to new architecture subtarget
features, and to have the CPUs inherit from this. ProcA9
(and similar) from what I could tell were only being used
for their enum value in making codegen decisions, hence I
moved all of the features they inherit over to the actual
CPUs for clarity, the idea being that all features a given
target uses come from a combination of the architecture it
inherits from and the target itself, not any intermediary
features like ProcA9.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I’m
not aware of any place where ProcA9 is getting used to get
subtarget features like this, and after a quick look I still
can’t find anything. Where exactly are you seeing ProcA9
being used to get features? Even so, the cortex-a9 processer
model itself inherits FeatureFP16 now so I would expect it
to use FP16, unless you’re not using cortex-a9 directly? (In
which case all CPUs that used to inherit ProcA9 now need to
inherit all of the features ProcA9 used to inherit as well
as ProcA9, which is what I did in the change you mention).<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Bradley
Smith<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">
Grang, Mandeep Singh [<a class="moz-txt-link-freetext" href="mailto:mgrang@codeaurora.org">mailto:mgrang@codeaurora.org</a>]
<br>
<b>Sent:</b> 24 February 2016 03:16<br>
<b>To:</b> Bradley Smith<br>
<b>Cc:</b> <a class="moz-txt-link-abbreviated" href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a><br>
<b>Subject:</b> Performance degradation on ARMv7
(cortex-a9)<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Hi Bradley,<br>
<br>
I was doing some performance analysis for ARMv7 (cortex-a9)
and I noticed that one of my benchmarks degraded by 93%. I
have tracked the regression down to the following commit by
you:<br>
<i><br>
commit 7c1b77248baaeafec5d6433c3d1da9a2e2b69595<br>
Author: Bradley Smith <a moz-do-not-send="true"
href="mailto:bradley.smith@arm.com"><bradley.smith@arm.com></a><br>
Date: Mon Nov 16 11:10:19 2015 +0000<br>
[ARM] Introduce subtarget features per ARM
architecture.<br>
This allows for accurate architecture targeting as
well as removing<br>
duplicate information (hardcoded feature strings) from
MCTargetDesc.</i><br>
<br>
I see that in lib/Target/ARM/ARM.td all the features have
been removed from Proc definition (e.g.: ProcA9) and added
to ProcessorModel definition (e.g.:
ProcessorModel<"cortex-a9").<br>
But I find that the features from Proc are still being read
and set in MCSubtargetInfo through the ARMFeatureKV table.
So if the Proc is empty the corresponding feature is not
being set.<br>
In my case, if I add FeatureFP16 back to the ProcA9
definition in ARM.td I get back all the lost performance.<br>
<br>
Could you please give me some insight on how, after your
change, do the Proc features get correctly set in
MCSubtargetInfo and other places which access Proc?<br>
<br>
Thanks,<br>
Mandeep<o:p></o:p></p>
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