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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi Alexandra,<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">I’m not sure want you want to do. Is the data layout string (<a href="http://llvm.org/docs/LangRef.html#datalayout">http://llvm.org/docs/LangRef.html#datalayout</a>,
also usually set by each target specific *TargetMachine constructor), for setting the alignment good enough for you?<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">Or is it more than the alignment you want to control? Do you have a target with 16-bit bytes? In that case, there is quite a lot of changes that needs to be
done (we maintain some patches internally that we can provide upon request).<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">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Patrik Hägglund<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""> llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu]
<b>On Behalf Of </b>Jimborean Alexandra<br>
<b>Sent:</b> den 22 november 2012 13:07<br>
<b>To:</b> llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> [LLVMdev] Set the minimum number of allocated bits for a variable<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" style="background:white"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">Hi,<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">I would like to force the minimum number of bits allocated for a variable in memory to be 16. From what I have seen, i1 is already represented on 8 bits. So, the
only change would be to represent i1 and i8 on 16 bits, as all other types already fulfill this condition.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">TargetData can help by setting a higher alignment, thus although the type is i1 or i8, the number of allocated bits is 16.
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">What is the best approach to impose this?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">(i) modifying the back-end of LLVM <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black"> - where can I find the defaults for specifying the number of allocated bits for each type?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">(ii) writing a pass that overwrites these defaults?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black"> - by asking for an alignment higher than the default<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black"> - one approach is to set a higher alignment for each allocated variable of type i1 or i8, but this means digging inside the arrays, vectors and structures to
check the type of each element.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black"> <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">Looking forward to receiving your suggestions.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">Thank you,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:black">Alexandra<o:p></o:p></span></p>
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