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<p class="MsoNormal"><span lang="SV">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="SV"><o:p> </o:p></span></p>
<p class="MsoNormal">I ran into MachineVerifier ”Virtual register killed in block, but needed live out.”
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">It was MachineSinking:PerformTrivialForwardCoalescing() that coalesced a COPY inside a single-block loop, but left the<o:p></o:p></p>
<p class="MsoNormal">kill-flag and then MachineVerifier complains that a register in vregsRequired is killed in MBB.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">In the example, %vreg520 is replaced by %vreg368 by PerformTrivialForwardCoalescing(), without clearing the kill flag:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">BB#13: derived from LLVM BB %CF250<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> Predecessors according to CFG: BB#12 BB#13 BB#14<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="SV" style="font-family:"Courier New""> …<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="SV" style="font-family:"Courier New""> %vreg520<def> = COPY %vreg368<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="SV" style="font-family:"Courier New""> %vreg568<def,tied1> = cmp %vreg341<tied0>, %vreg520<kill><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="SV" style="font-family:"Courier New""> </span>
<span style="font-family:"Courier New"">brr_cond <BB#13><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> brr_uncond <BB#14><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> Successors according to CFG: BB#13, BB#14<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Into <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">BB#13: derived from LLVM BB %CF250<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> Predecessors according to CFG: BB#12 BB#13 BB#14<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="SV" style="font-family:"Courier New""> …<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="SV" style="font-family:"Courier New""> %vreg568<def,tied1> = cmp %vreg341<tied0>, %vreg368<kill><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="SV" style="font-family:"Courier New""> </span>
<span style="font-family:"Courier New"">brr_cond <BB#13><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""> brr_uncond <BB#14><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">=><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">*** Bad machine code: Virtual register killed in block, but needed live out. ***<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">- function: autogen_SD15028<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">- basic block: BB#13 CF250 (0x1c75890)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">Virtual register %vreg368 is used after the block.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal">There is only one use of %vreg368 in the function.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">One thing that strikes me is that one might want to clear the kill flag for a use inside a loop of a register defined prior to
<o:p></o:p></p>
<p class="MsoNormal">the loop?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Best regards,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Jonas Paulsson<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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