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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Maybe it would be easier to provide a bitcode example of this problem.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">After thinking about this more, I’m not sure if this is applicable to SPIR itself. For you to have a constant GEP expression, you have to know the pointer size
in order to correctly generate the expression. Since the pointer size itself is not known, I don’t yet see how you can generate a constant expression that is valid SPIR.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Micah<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"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> mankeyrabbit@gmail.com [mailto:mankeyrabbit@gmail.com]
<b>On Behalf Of </b>James Molloy<br>
<b>Sent:</b> Saturday, September 29, 2012 5:30 AM<br>
<b>To:</b> Owen Anderson<br>
<b>Cc:</b> Villmow, Micah; llvmdev@cs.uiuc.edu; pocl-devel@lists.sourceforge.net; cfe-dev@cs.uiuc.edu<br>
<b>Subject:</b> Re: [LLVMdev] [pocl-devel] [cfe-dev] SPIR provisional specification is now available in the Khronos website<o:p></o:p></span></p>
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<p class="MsoNormal">Yes, it would.<o:p></o:p></p>
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<p class="MsoNormal">But I was concerned Micah was just going to write it off as an implementation detail, so I felt that I should offer a "less correct but less work" option for him to consider.<o:p></o:p></p>
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<p class="MsoNormal">Cheers,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">James<o:p></o:p></p>
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<p class="MsoNormal">On 29 September 2012 03:16, Owen Anderson <<a href="mailto:resistor@mac.com" target="_blank">resistor@mac.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">On Sep 28, 2012, at 9:45 AM, James Molloy <<a href="mailto:james@jamesmolloy.co.uk" target="_blank">james@jamesmolloy.co.uk</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:13.5pt;font-family:"Helvetica","sans-serif"">You can easily simplify this problem with a restriction in SPIR: disallow ConstantExpr casts - no ptrtoint constant expression. Because GlobalVariables have pointer type,
if you disallow converting their type to non-pointer type in a constantexpr, the number of constantexpr subclasses you have to deal with is drastically reduced (to essentially just BitCast and GEP).</span><o:p></o:p></p>
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<p class="MsoNormal">Wouldn't an easier solution just be not to represent them as constants in the first place? For instance, you could have a built-in function to get the address of local N, where N is taken as a parameter. You can call the builtins at the
beginning of the kernel, and then proceed to use them as you wish without having to worry about reversing a constant folding later. Plus, if a given vendor's backend
<i>wants</i> the address to get constant folded, it's easy to do replaceAllUsesWith of the call with a global, and run an appropriate constant folding pass.<o:p></o:p></p>
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<p class="MsoNormal"><span style="color:#888888"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:#888888">--Owen<o:p></o:p></span></p>
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