<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: arial,helvetica,sans-serif; font-size: 10pt; color: #000000'><br><br><hr id="zwchr"><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px; color: rgb(0, 0, 0); font-weight: normal; font-style: normal; text-decoration: none; font-family: Helvetica,Arial,sans-serif; font-size: 12pt;"><b>From: </b>"Sean Silva via llvm-commits" <llvm-commits@lists.llvm.org><br><b>To: </b>"Justin Bogner" <mail@justinbogner.com><br><b>Cc: </b>"llvm-commits" <llvm-commits@lists.llvm.org><br><b>Sent: </b>Tuesday, May 10, 2016 4:55:08 PM<br><b>Subject: </b>Re: [llvm] r268452 - PM: Port LoopRotation to the new loop pass manager<br><br><div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, May 10, 2016 at 12:46 PM, Justin Bogner <span dir="ltr"><<a href="mailto:mail@justinbogner.com" target="_blank">mail@justinbogner.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div class="HOEnZb"><div class="h5">Sean Silva <<a href="mailto:chisophugis@gmail.com" target="_blank">chisophugis@gmail.com</a>> writes:<br>
> On Tue, May 10, 2016 at 11:27 AM, Justin Bogner <<a href="mailto:mail@justinbogner.com" target="_blank">mail@justinbogner.com</a>><br>
> wrote:<br>
><br>
>> Sean Silva <<a href="mailto:chisophugis@gmail.com" target="_blank">chisophugis@gmail.com</a>> writes:<br>
>> > On Tue, May 3, 2016 at 3:02 PM, Justin Bogner via llvm-commits <<br>
>> > <a href="mailto:llvm-commits@lists.llvm.org" target="_blank">llvm-commits@lists.llvm.org</a>> wrote:<br>
>> ><br>
>> >> Author: bogner<br>
>> >> Date: Tue May 3 17:02:31 2016<br>
>> >> New Revision: 268452<br>
>> >><br>
>> >> URL: <a href="http://llvm.org/viewvc/llvm-project?rev=268452&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-project?rev=268452&view=rev</a><br>
>> >> Log:<br>
>> >> PM: Port LoopRotation to the new loop pass manager<br>
>> ...<br>
>> >> --- llvm/trunk/test/Transforms/LoopRotate/basic.ll (original)<br>
>> >> +++ llvm/trunk/test/Transforms/LoopRotate/basic.ll Tue May 3 17:02:31<br>
>> 2016<br>
>> >> @@ -1,4 +1,6 @@<br>
>> >> ; RUN: opt -S -loop-rotate < %s | FileCheck %s<br>
>> >> +; RUN: opt -S<br>
>> >><br>
>> -passes='require<loops>,require<targetir>,require<assumptions>,loop(rotate)'<br>
>> >> < %s | FileCheck %s<br>
>> >><br>
>> ><br>
>> > Sorry if this is a stupid question, but why do we need to explicitly<br>
>> > "require" the passes when the loop-rotate already declares the<br>
>> dependency?<br>
>> > (I feel like there's some part of the bigger picture that I'm missing<br>
>> here)<br>
>><br>
>> To be clear, there are no dependencies in the new pass manager - passes<br>
>> request analysis results from an analysis manager and they're calculated<br>
>> or returned from the cache as appropriate. Naturally, the next question<br>
>> one would ask is "okay then, why aren't these calculated on demand when<br>
>> loop-rotate asks for them?".<br>
>><br>
><br>
> Ah, yeah. The whole "schedule vs. cache" is one of the main differences of<br>
> the new PM.<br>
><br>
><br>
>><br>
>> The mechanical answer is that loop-rotate uses the `getCachedResult`<br>
>> API, not the `getResult` one - the difference being that<br>
>> `getCachedResult` only returns results if they're already calculated,<br>
>> and null otherwise. Hence, without the require<> in the test, there are<br>
>> no results.<br>
><br>
><br>
> Ah, makes perfect sense!<br>
><br>
><br>
>> This of course leads to "why does loop-rotate use<br>
>> getCachedResult?"<br>
>><br>
>> It has to. These analyses are function analyses, and a loop pass isn't<br>
>> allowed to cause a function analysis to run, much like a function pass<br>
>> isn't allowed to cause a module analysis to be run. They have to stick<br>
>> to their own level. This enforces correct layering and acts as a<br>
>> safeguard against accidentally doing extra work.<br>
>><br>
>> That said, the "require<loops>" is redundant, since a LoopPassManager<br>
>> can't operate without having calculated that. There may also be an<br>
>> argument to be made that the LPM should implicitly calculate some other<br>
>> analyses, but we'd have to be careful not to do too much.<br>
>><br>
><br>
> Makes sense. But then `+ assert((LI && TTI && AC) && "Analyses for loop<br>
> rotation not available");` is not really appropriate, right? Can't we hit<br>
> that assert just by passing the right arguments to opt? (by dropping the<br>
> `require<*>` analyses from the passes= specification?)<br>
><br>
> (sorry, I'm away from the office and don't have an easy way to test locally)<br>
<br>
</div></div>Yes it does. The other option is to just bail on the transform in that<br>
case, which would be a better option for things like fuzzers and<br>
bisection scripts, but makes it harder to ensure we're doing everything<br>
correctly while we're bringing this up. For now I think the assert is<br>
best, but we may want to revisit this at some point.<br>
</blockquote></div><br></div><div id="DWT15810" class="gmail_extra">I'm uncomfortable with the assert because it won't be there in Release and I don't want to be running into UB in my release build from a mistyped command line. I think report_fatal_error is more appropriate.</div></div></blockquote>+1<br><br>Also, we might want to consider moving the error-reporting logic into the pass manager itself. I could see having a 'Required' parameter to getCachedResult such that it would be a fatal error should no cached result be available.<br><br> -Hal<br><blockquote style="border-left: 2px solid rgb(16, 16, 255); margin-left: 5px; padding-left: 5px; color: rgb(0, 0, 0); font-weight: normal; font-style: normal; text-decoration: none; font-family: Helvetica,Arial,sans-serif; font-size: 12pt;"><div dir="ltr"><div class="gmail_extra"></div><div class="gmail_extra"><br></div></div>
<br>_______________________________________________<br>llvm-commits mailing list<br>llvm-commits@lists.llvm.org<br>http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits<br></blockquote><br><br><br>-- <br><div><span name="x"></span>Hal Finkel<br>Assistant Computational Scientist<br>Leadership Computing Facility<br>Argonne National Laboratory<span name="x"></span><br></div></div></body></html>