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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">GCC does the same thing. I haven't found anything written down that explains this yet but I believe it's that PIC consistently generates faster and smaller code than non-PIC
for N64.<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"">For example, a non-PIC implementation of getAddrLocal() would probably generate something like this:<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:36.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">lui $1, %highest(foo)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:36.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">add $1, $1, %higher(foo)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:36.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">dsll $1, $1, 32<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:36.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">lui $2, %hi(foo)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:36.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">add $2, $2, %lo(foo)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:36.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">add $1, $1, $2<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">which is 6 instructions per-symbol referenced. The current PIC implementation generates this:<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:36.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">lui $1, %hi(%neg(%gp_rel(bar)))<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:36.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">daddu $1, $1, $25<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:36.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">daddiu $1, $1, %lo(%neg(%gp_rel(bar)))<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:36.0pt"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">ld $2, %got_disp(foo)($1)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">which is a one-time cost of 3 instructions to set up the GOT pointer, plus one load per-symbol referenced.<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 lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" 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>Brandon Hill<br>
<b>Sent:</b> 29 April 2014 22:35<br>
<b>To:</b> llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> [LLVMdev] MIPS n64 ABI and non-PIC<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">Has anyone experimented with generating non-PIC for MIPS64 and the n64 ABI? Currently MipsISelLowering.cpp uses conditions like:<br>
<br>
if ((getTargetMachine().getRelocationModel() == Reloc::PIC_) || IsN64) {<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" style="margin-bottom:12.0pt">around any PIC code generation. Is generating non-PIC just untested, or is it known not to work? I can't find any discussion of it anywhere. I ran into this when trying to see why --relocation-model=static
had no effect on the output. I'm game to test it, but it would help to know that it isn't pointless due to a significant known issue.<o:p></o:p></p>
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<p class="MsoNormal">Brandon<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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