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<p class="MsoNormal"><span style="font-size:11.0pt">Hey all,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">I'm looking to extend the current clang loop pragmas to also support hardware loops and allow a user to insert (or completely disable) hardware loop intrinsics on a per-loop basis.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">One of the questions I have regarding this is how to go about incorporating the different hardware loop intrinsics in the pragma. A few options we came up with:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">1. The pragma incorporates which intrinsic to use for a loop:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">#pragma loop hwloop(set_loop_i32)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">or<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">#pragma loop hwloop(/*LivesInReg=*/ true, /*AddTestGuard=*/ true, /*NumBits=*/ 32)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">2. The pragma adds some target specific info (string?) to use in the hwloop TTI hook/new hwloop TTI hook:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">#pragma loop hwloop(target="bdnz") // PPC example<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">#pragma loop hwloop(target="bdz") // PPC example<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">or<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">#pragma loop hwloop(max-count=42, ...)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Option 1 requires the user to know about llvm's hardware loops internals so I'm leaning more towards option 2 as users are more likely to be aware of target specific information (such as PPC's bdnz/bdz).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">These are just some options we came up with, we would love to hear about other (better) options, if any.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Kind regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Janek van Oirschot<o:p></o:p></span></p>
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