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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi Hao,<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">You are right, the IR is not “target independent” in the strict sense.<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">There’s a fairly old post that explains this (amongst other things) in detail:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><a href="http://lists.cs.uiuc.edu/pipermail/llvmdev/2011-October/043719.html">http://lists.cs.uiuc.edu/pipermail/llvmdev/2011-October/043719.html</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">x86_fp80 is just one example of this.<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">It is kind-of-possible to restrict LLVM IR to be sort-of-target-independent (look up Portable Native Client and SPIR for details), but an arbitrary IR file
generated by a front-end that had target X in mind is not guaranteed to work as you’d expect if you use backend Y.<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></a></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Michael<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"><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""> llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu]
<b>On Behalf Of </b>Hao Wang<br>
<b>Sent:</b> Tuesday, December 09, 2014 09:33<br>
<b>To:</b> llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> [LLVMdev] The target independence of IR<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="line-height:115%">Hi, <o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%"><o:p> </o:p></p>
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<p class="MsoNormal" style="line-height:115%">Can anyone help me understand that LLVM IR has "target independence" ?<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%"><o:p> </o:p></p>
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<p class="MsoNormal" style="line-height:115%">1. When we talk about "target", we mean something like Instruction Set Architecture ?<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%"><o:p> </o:p></p>
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<p class="MsoNormal" style="line-height:115%">2. The front-end may generate IR code such as x86_fp80, so the IR is actually not fully target-independent? It contains information about the target, and the front-end should also be aware of this?<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%"><o:p> </o:p></p>
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<p class="MsoNormal" style="line-height:115%">Thank you!<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%"><o:p> </o:p></p>
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<p class="MsoNormal" style="line-height:115%">Hao <o:p></o:p></p>
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