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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">What about the part about address spaces with pointers of different sizes?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Micah<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""><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""> Mon Ping Wang [mailto:monping@apple.com]
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<b>Sent:</b> Friday, September 07, 2012 3:19 PM<br>
<b>To:</b> Villmow, Micah<br>
<b>Cc:</b> llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> Re: [LLVMdev] Bitcasts between pointers with different address spaces<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hi,<o:p></o:p></p>
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<p class="MsoNormal">I don't think we should make bit casts between pointers with different address spaces illegal. Address spaces are not required to be disjoint. In the N1169 spec, it says <o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica","sans-serif""> A non-null pointer into an address space
<i>A </i>can be cast to a pointer into another address space <i>B, </i>but such a cast is undefined if the source pointer does not point to a location in
<i>B. </i></span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">If the address spaces overlap, one should be able to bticast between them. <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-- Mon Ping<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Sep 7, 2012, at 10:47 AM, Villmow, Micah wrote:<o:p></o:p></p>
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<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Should LLVM make bitcasts between pointers with different address spaces illegal?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">This will require a small clarification in the documentation and an assertion check added to the verifier, but I think this would be a good approach.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">The reason being is that in different address spaces, pointers are not always the same size.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">This could be limited to make it legal only if the size of the pointer in source and destination address spaces are equivalent, but that seems like more of a work-around
than a proper solution.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Ideas?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Micah<o:p></o:p></span></p>
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<p class="MsoNormal">_______________________________________________<br>
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<a href="http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev">http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev</a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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