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<p class="MsoNormal">I’ve ran into this situation for our out-of-tree target.<o:p></o:p></p>
<p class="MsoNormal">(The first part is just some background info describing what is happening. My actual questions are at the end.)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">We got an instruction like this during register coalescing<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">288B %19:an40_0_7, dead %23.hiAcc40:an40pairs = div_i32_p4 %23.hiAcc40:an40pairs, %22:an40_0_7<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">and the we get this merge:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Considering merging to aN40Pairs with %19 in %23:loAcc40<o:p></o:p></p>
<p class="MsoNormal"> RHS = %19 [128r,160B:1)[288r,400B:0)[400B,480r:2) 0@288r 1@128r 2@400B-phi weight:0.000000e+00<o:p></o:p></p>
<p class="MsoNormal"> LHS = %23 [16r,288r:2)[288r,288d:4)[320r,400B:3)[400B,480r:0)[480r,496r:1) 0@400B-phi 1@480r 2@16r 3@320r 4@288r weight:0.000000e+00<o:p></o:p></p>
<p class="MsoNormal"> merge %19:2@400B into %23:0@400B --> @400B<o:p></o:p></p>
<p class="MsoNormal"> merge %23:1@480r into %19:2@400B --> @400B<o:p></o:p></p>
<p class="MsoNormal"> merge %23:4@288r into %19:0@288r --> @288r<o:p></o:p></p>
<p class="MsoNormal"> pruned %19 at 320r: [128r,160B:1)[288r,320r:0)[400B,480r:2) 0@288r 1@128r 2@400B-phi<o:p></o:p></p>
<p class="MsoNormal"> pruned all of %23 at 288r: [16r,288r:2)[320r,400B:3)[400B,480r:0)[480r,496r:1) 0@400B-phi 1@480r 2@16r 3@320r 4@288r<o:p></o:p></p>
<p class="MsoNormal"> pruned %23 at 128r: [16r,128r:2)[160B,288r:2)[320r,400B:3)[400B,480r:0)[480r,496r:1) 0@400B-phi 1@480r 2@16r 3@320r 4@288r<o:p></o:p></p>
<p class="MsoNormal"> erased: 480r %23.acc:an40pairs = COPY %19.acc:an40_0_7<o:p></o:p></p>
<p class="MsoNormal"> restoring liveness to 5 points: 400B,320r,288d,160B,128r: %23 [16r,128r:1)[128r,160B:4)[160B,288r:1)[288r,320r:2)[320r,400B:3)[400B,496r:0) 0@400B-phi 1@16r 2@288r 3@320r 4@128r weight:0.000000e+00<o:p></o:p></p>
<p class="MsoNormal"> updated: 128B %23.acc:an40pairs = mv32Imm_pseudo -1<o:p></o:p></p>
<p class="MsoNormal"> updated: 288B %23.loAcc40:an40pairs, dead %23.hiAcc40:an40pairs = div_i32_p4 %23.hiAcc40:an40pairs, %22:an40_0_7<o:p></o:p></p>
<p class="MsoNormal"> updated: 320B %23.hiAcc40_then_acc:an40pairs = shfts %23. loAcc40_then_acc:an40pairs, -31<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">so after coalescing we have<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">288B %23.loAcc40:an40pairs, dead %23.hiAcc40:an40pairs = div_i32_p4 %23.hiAcc40:an40pairs, %22:an40_0_7<o:p></o:p></p>
<p class="MsoNormal">********** INTERVALS **********<o:p></o:p></p>
<p class="MsoNormal">%22 [192r,288r:0)[288r,288d:1) 0@192r 1@288r weight:0.000000e+00<o:p></o:p></p>
<p class="MsoNormal">%23 [16r,128r:1)[128r,160B:4)[160B,288r:1)[288r,320r:2)[320r,400B:3)[400B,496r:0) 0@400B-phi 1@16r 2@288r 3@320r 4@128r weight:0.000000e+00<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">And we get *** Bad machine code: Live range continues after dead def flag ***<o:p></o:p></p>
<p class="MsoNormal">(the loAcc40 subregister is live out and used later, while the hiAcc40 subregister is dead)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">My questions are:<br>
<br>
<o:p></o:p></p>
<ol style="margin-top:0cm" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo2">We are not tracking subregister liveness for our target. So should it be allowed to have “%23.loAcc40:an40pairs, dead %23.hiAcc40:an40pairs = …”? (What is the semantics for that?)<br>
<br>
<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo2">Is the semantics of a “dead” subregister def different for “tracks subregister liveness” enable and disabled?
<br>
<br>
<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l1 level1 lfo2">Would it be correct to remove the “dead” marking for %23.hiAcc40:an40pairs in my problem above (at least with subregister liveness disabled)? Or is the verifier that is too restrictive
here?<o:p></o:p></li></ol>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Regards,<o:p></o:p></p>
<p class="MsoNormal">Björn<o:p></o:p></p>
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