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<p class="MsoNormal">Hi,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">My backend (based on version 3.8) was hanging in an infinite loop in the Prolog/Epilog Inserter.<o:p></o:p></p>
<p class="MsoNormal">After investigation, it appears that it was looping in the first level loop of the PEI::replaceFrameIndices() method: processing the second instruction of the block again and again…<o:p></o:p></p>
<p class="MsoNormal">This loop never exits because the iterator is ‘skipped backward’ under some condition in the middle of the loop (see yellow highlighted line).<o:p></o:p></p>
<p class="MsoNormal">I understand the rationale explained in the first comment, but I don’t understand how the condition (“not the first instruction”) is related to this rationale.<o:p></o:p></p>
<p class="MsoNormal">I have commented out the iterator decrement and then my back-end behave correctly.<o:p></o:p></p>
<p class="MsoNormal">The handling of this loop iterator is quite complex: skipping backward or forward in not so clearly raised conditions.<o:p></o:p></p>
<p class="MsoNormal">Could someone review the logic of this iterator to confirm its correctness? Or is it a bug?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><span style="font-size:10.0pt;font-family:Monospace;color:#3F7F5F">// Some instructions (e.g.
<u>inline</u> <u>asm</u> instructions) can have</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><span style="font-size:10.0pt;font-family:Monospace;color:#3F7F5F">// multiple frame indices and/or cause eliminateFrameIndex</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><span style="font-size:10.0pt;font-family:Monospace;color:#3F7F5F">// to insert more than one instruction. We need the register</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><span style="font-size:10.0pt;font-family:Monospace;color:#3F7F5F">// scavenger to go through all of these instructions so that</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><span style="font-size:10.0pt;font-family:Monospace;color:#3F7F5F">// it can update its register information. We keep the</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><span style="font-size:10.0pt;font-family:Monospace;color:#3F7F5F">// iterator at the point before insertion so that we can</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black"> </span><span style="font-size:10.0pt;font-family:Monospace;color:#3F7F5F">// revisit them in full.</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><b><span style="font-size:10.0pt;font-family:Monospace;color:#7F0055">bool</span></b><span style="font-size:10.0pt;font-family:Monospace;color:black"> AtBeginning = (I == BB->begin());</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><b><span style="font-size:10.0pt;font-family:Monospace;color:#7F0055;background:yellow;mso-highlight:yellow">if</span></b><span style="font-size:10.0pt;font-family:Monospace;color:black;background:yellow;mso-highlight:yellow"> (!AtBeginning) --I;</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><span style="font-size:10.0pt;font-family:Monospace;color:#3F7F5F">// If this instruction has a FrameIndex operand, we need to</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><span style="font-size:10.0pt;font-family:Monospace;color:#3F7F5F">// use that target machine register info object to eliminate</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><span style="font-size:10.0pt;font-family:Monospace;color:#3F7F5F">// it.</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:Monospace;color:black"> TRI.eliminateFrameIndex(MI, SPAdj, i,</span><span style="font-size:10.0pt;font-family:Monospace"><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:10.0pt;font-family:Monospace;color:black">
</span><span style="font-size:10.0pt;font-family:Monospace;color:#0000C0">FrameIndexVirtualScavenging</span><span style="font-size:10.0pt;font-family:Monospace;color:black"> ?
</span><b><span style="font-size:10.0pt;font-family:Monospace;color:#7F0055">nullptr</span></b><span style="font-size:10.0pt;font-family:Monospace;color:black"> :
</span><span style="font-size:10.0pt;font-family:Monospace;color:#0000C0">RS</span><span style="font-size:10.0pt;font-family:Monospace;color:black">);</span><span style="font-size:12.0pt;font-family:"Times New Roman","serif""><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-bottom:12.0pt"><span style="font-size:12.0pt;font-family:"Times New Roman","serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="FR-BE">Regards, Dominique Torette.</span><span lang="FR-BE" style="font-size:12.0pt;font-family:"Times New Roman","serif""><br>
<br>
<br>
<br>
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman","serif""><img width="536" height="49" id="_x0000_i1025" src="http://www.spacebel.be/wp-content/uploads/2011/06/image-sign-sbp.jpg" alt="http://www.spacebel.be/wp-content/uploads/2011/06/image-sign-sbp.jpg"></span><span lang="FR-BE" style="font-size:12.0pt;font-family:"Times New Roman","serif""><o:p></o:p></span></p>
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<p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;text-align:center">
<b><span lang="FR-BE" style="font-size:10.0pt">Dominique Torette</span></b><span lang="FR-BE" style="font-size:10.0pt">
<br>
System Architect<br>
Rue des Chasseurs Ardennais - Liège Science Park - B-4031 Angleur <br>
Tel: +32 (0) 4 361 81 11 - Fax: +32 (0) 4 361 81 20 <br>
</span><span style="font-size:10.0pt"><a href="http://www.spacebel.be/"><span lang="FR-BE" style="color:blue">www.spacebel.be</span></a></span><span lang="FR-BE" style="font-size:12.0pt;font-family:"Times New Roman","serif""><o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="FR-BE"><o:p> </o:p></span></p>
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