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<div class="" style="word-wrap:break-word">Hi,
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<div class="">I have been wrestling with a bug that the LLVM compiler has. The target architecture is an ultra wide SIMD with two issue slots. A CP that is responsible for the control flow and a wide array of PE elements. I am currently working on this compiler
for my graduation project at the Eindhoven University of Technology in the Netherlands.</div>
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<div class="">Perhaps some of you have seen this error before or maybe someone has any idea on how to fix it?</div>
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<div class="">From the debug information I can deduce that the register allocator tries to rewrites two operations, but that is where it goes wrong.</div>
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This is a snippet taken from the debug information.</div>
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spillAroundUses %vreg78</div>
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rewrite: 1360r<span class="x_Apple-tab-span" style="white-space:pre"> </span>%vreg140<def> = VSFGTSP0vv %vreg53, %vreg77; VP0Regs:%vreg140 VRegs:%vreg53,%vreg77</div>
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spill: </div>
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reload: </div>
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rewrite: 1512r<span class="x_Apple-tab-span" style="white-space:pre"> </span>%vreg79<def> = VCMOVvv %vreg141<kill>, %vreg76, %vreg77; VRegs:%vreg79,%vreg76,%vreg77 VP0Regs:%vreg141</div>
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<div class=""><i class="">This is before it is rewritten:</i></div>
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<b class=""><font color="#ff2600" class="">%vreg78</font><font color="#454545" class=""><def> = VSFGTSP0vv %vreg53, %vreg77; VP0Regs:%vreg78 VRegs:%vreg53,%vreg77</font></b></div>
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%vreg80<def> = COPY %vreg134; VRegs:%vreg80 GRegs:%vreg134</div>
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%vreg76<def> = VCMOVvv %vreg75, %vreg53, %vreg74; VRegs:%vreg76,%vreg53,%vreg74 VP0Regs:%vreg75</div>
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%vreg85<def> = ADDrr %vreg3, %vreg134; GRegs:%vreg85,%vreg3,%vreg134</div>
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%vreg81<def> = VSFLTSP0vv %vreg65, %vreg74; VP0Regs:%vreg81 VRegs:%vreg65,%vreg74</div>
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%vreg83<def> = VSFGTSP0vv %vreg65, %vreg77; VP0Regs:%vreg83 VRegs:%vreg65,%vreg77</div>
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%vreg86<def> = COPY %vreg85; VRegs:%vreg86 GRegs:%vreg85</div>
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<b class=""><font color="#454545" class="">%vreg79<def> = VCMOVvv </font><font color="#ff2600" class="">%vreg78</font><font color="#454545" class="">, %vreg76, %vreg77; VRegs:%vreg79,%vreg76,%vreg77 VP0Regs:</font><font color="#ff2600" class="">%vreg78</font></b></div>
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<i class="">This is after it is rewritten:</i></div>
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<font color="#ff2600" class=""><b class="">%vreg140</b></font><span class="" style="color:rgb(69,69,69)"><b class=""><def,dead> = VSFGTSP0vv %vreg53, %vreg77; VP0Regs:%vreg140 VRegs:%vreg53,%vreg77</b></span></div>
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%vreg80<def> = COPY %vreg134; VRegs:%vreg80 GRegs:%vreg134<b class=""></b></div>
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%vreg76<def> = VCMOVvv %vreg75, %vreg53, %vreg74; VRegs:%vreg76,%vreg53,%vreg74 VP0Regs:%vreg75</div>
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%vreg85<def> = ADDrr %vreg3, %vreg134; GRegs:%vreg85,%vreg3,%vreg134</div>
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%vreg81<def> = VSFLTSP0vv %vreg65, %vreg74; VP0Regs:%vreg81 VRegs:%vreg65,%vreg74</div>
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%vreg83<def> = VSFGTSP0vv %vreg65, %vreg77; VP0Regs:%vreg83 VRegs:%vreg65,%vreg77</div>
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%vreg86<def> = COPY %vreg85; VRegs:%vreg86 GRegs:%vreg85</div>
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<b class=""><font color="#454545" class="">%vreg79<def> = VCMOVvv </font><font color="#ff2600" class="">%vreg141</font><font color="#454545" class="">, %vreg76, %vreg77; VRegs:%vreg79,%vreg76,%vreg77 VP0Regs:</font><font color="#ff2600" class="">%vreg141</font></b></div>
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So, it seems to accidentally create a new virtual register for the second operation that is rewritten. Maybe, it should have used
<i class="">%vreg140</i>.</div>
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Any thoughts?</div>
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Cheers,</div>
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Guus Leijsten</div>
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P.S. There are 2 txt files attached to this email. One contains the actual error that “Bad machine code: Reading virtual register without a def”, and the other file has a selection of the debug information. </div>
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