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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D">I mean something like a target-specific fence machine instruction which forces ordering of all loads/stores. I want to clarify the meaning of “noalias” in
this case. Is the fence machine instruction considered “touching” all memory and thus breaks the “noalias” contract?<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">Xiaoyi<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"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Eli Friedman [mailto:eli.friedman@gmail.com]
<br>
<b>Sent:</b> Wednesday, June 12, 2013 8:08 PM<br>
<b>To:</b> Guo, Xiaoyi<br>
<b>Cc:</b> LLVM Dev<br>
<b>Subject:</b> Re: [LLVMdev] A question w.r.t fence instruction vs. noalias pointer<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Wed, Jun 12, 2013 at 7:28 PM, Guo, Xiaoyi <<a href="mailto:Xiaoyi.Guo@amd.com" target="_blank">Xiaoyi.Guo@amd.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">So fence only forces ordering of atomic instructions.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Let me change my question then.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">If I have a target-specific intrinsic which forces ordering of ordinary load/store instructions.
Then should it also force ordering of load/stores to noalias pointers in caller functions?</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" style="margin-bottom:12.0pt">So, something like 'asm volatile ("":::"memory")'?<o:p></o:p></p>
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<p class="MsoNormal">LLVM can and will move noalias loads/stores across an asm statement like this; it assumes noalias means "nothing inside this function will touch the memory in question except accesses through this pointer".<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-Eli<o:p></o:p></p>
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