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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Ok, I didn't know that. It looks like gcc's behaviour is triple-dependent. My mips-mti-linux-gnu-gcc toolchain (last updated in January) always generates PIC code for –fPIC,
-fno-PIC, and neither option. I've just tried the latest mips-sde-elf-gcc toolchain and found it emits non-PIC code for –fno-PIC and neither option, and errors out with –fPIC (without additional options).<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""> Brandon Hill [mailto:bgh.list.reader@gmail.com]
<br>
<b>Sent:</b> 02 May 2014 19:53<br>
<b>To:</b> Daniel Sanders<br>
<b>Cc:</b> llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> Re: [LLVMdev] MIPS n64 ABI and non-PIC<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Actually, GCC will generate non-PIC for n64. Maybe that is a recent addition, but we are using its results. Even if PIC may be faster and smaller code, it seems that non-PIC is still useful for bare-metal.
That's the driver of my interest. I guess we can just test what happens when that part of the conditional is removed. As a side note, if it isn't supported then we should probably have the compiler warn the user that the two flags aren't compatible.<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" style="margin-bottom:12.0pt"><o:p> </o:p></p>
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<p class="MsoNormal">On Wed, Apr 30, 2014 at 2:25 AM, Daniel Sanders <<a href="mailto:Daniel.Sanders@imgtec.com" target="_blank">Daniel.Sanders@imgtec.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"">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.</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""> </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"">For example, a non-PIC implementation of getAddrLocal() would probably generate something like this:</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;text-indent:36.0pt">
<span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">lui $1, %highest(foo)</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">add $1, $1, %higher(foo)</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">dsll $1, $1, 32</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">lui $2, %hi(foo)</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">add $2, $2, %lo(foo)</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">add $1, $1, $2</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"">which is 6 instructions per-symbol referenced. The current PIC implementation generates this:</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">lui $1, %hi(%neg(%gp_rel(bar)))</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">daddu $1, $1, $25</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">daddiu $1, $1, %lo(%neg(%gp_rel(bar)))</span><o:p></o:p></p>
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<span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">ld $2, %got_disp(foo)($1)</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"">which is a one-time cost of 3 instructions to set up the GOT pointer, plus one load per-symbol referenced.</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""> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><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"">
<a href="mailto:llvmdev-bounces@cs.uiuc.edu" target="_blank">llvmdev-bounces@cs.uiuc.edu</a> [mailto:<a href="mailto:llvmdev-bounces@cs.uiuc.edu" target="_blank">llvmdev-bounces@cs.uiuc.edu</a>]
<b>On Behalf Of </b>Brandon Hill<br>
<b>Sent:</b> 29 April 2014 22:35<br>
<b>To:</b> <a href="mailto:llvmdev@cs.uiuc.edu" target="_blank">llvmdev@cs.uiuc.edu</a><br>
<b>Subject:</b> [LLVMdev] MIPS n64 ABI and non-PIC</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">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" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> }<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;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" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Brandon<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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