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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Ping. Anyone have any idea on how to fix this?<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Thanks,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Micah<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> llvmdev-bounces@cs.uiuc.edu
[mailto:llvmdev-bounces@cs.uiuc.edu] <b>On Behalf Of </b>Villmow, Micah<br>
<b>Sent:</b> Wednesday, April 14, 2010 2:28 PM<br>
<b>To:</b> llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> Re: [LLVMdev] Default behavior of DeadMachineInstructionElim
deletes all instructions<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Dale,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'> Yeah that is correct, so that isn’t the problem, not sure
why I was thinking it is. The !MRI->use_no_dbg_empty(Reg) seems to be
correct and the problem is LivePhysRegs[Reg] always returning false. I’ve
looked into this more and there is a part where I’m working with physical
registers. <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>If there is a function call, there is a copy from virtual
register space to the functions that are expected to be passed into the
register. <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>So it looks something like this:<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>… do some work …<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Mov %r0, %r1025<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Mov %r1, %r1026<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Mov %r2, %r1027<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Call someFunc %r0, %r1, %r2 </span><span style='font-size:11.0pt;
font-family:Wingdings;color:#1F497D'>ß</span><span style='font-size:11.0pt;
font-family:"Calibri","sans-serif";color:#1F497D'> this func stores to memory<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Ret<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>The moves to the physical registers are being deleted as
NonAllocatableRegs is set to all one’s and then inverted, and since these are
deleted, every instruction that they depended on is also deleted.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>I have a workaround(disable the pass), but I’d much rather
figure out what I am doing incorrectly that is causing this behavior or if
determining if the default assumptions by this pass are correct.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Micah<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Dale Johannesen
[mailto:dalej@apple.com] <br>
<b>Sent:</b> Wednesday, April 14, 2010 2:15 PM<br>
<b>To:</b> Villmow, Micah<br>
<b>Cc:</b> Dale Johannesen; llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> Re: [LLVMdev] Default behavior of DeadMachineInstructionElim
deletes all instructions<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<div>
<div>
<p class=MsoNormal>On Apr 14, 2010, at 1:55 PMPDT, Villmow, Micah wrote:<o:p></o:p></p>
</div>
<p class=MsoNormal style='margin-bottom:12.0pt'><o:p> </o:p></p>
<div>
<div>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>I’ve
recently sync’d to a newer version of LLVM(Apple branch 2326 from Apple branch
2323.8) that changed the interface to addCommonCodeGenPasses which caused the
default implementation to be executed instead of my overriding implementation.
This default implementation has DeadMachineInstructionElim pass enabled, which
is causing havoc with my backend. Before entering this pass, everything in my
machine function is fine, after this pass, all instructions that are not
function calls are deleted. I’ve tracked this issue down to the line:<o:p></o:p></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>BitVector
NonAllocatableRegs = TRI->getAllocatableSet(MF); (In my case all registers
defined in RegisterInfo.td)<o:p></o:p></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>This
function loops through all registers classes and sets all registers in the
bitset that are allocatable. It then inverts the registers that are set to get
the NonAllocatable registers and assigns that to the LivePhysRegs for each
basic block in a function. The function then loops through all instructions in
a basic block and checks to see if it is a dead instruction. The check is
whether it is a physical register or not with the check:<o:p></o:p></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>TargetRegisterInfo::isPhysicalRegister(reg)
? LivePhysRegs[Reg] : !MRI->use_nodbg_empty(Reg) <o:p></o:p></p>
<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>If
the register is virtual, then MRI->use_nodbg_empty() returns false, if the
register is physical LivePhysRegs[Reg] returns false, since the bitvector was
inverted. So my instruction is considered dead and deleted.<o:p></o:p></p>
</div>
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<p class=MsoNormal>Huh? The code is<o:p></o:p></p>
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<div>
<p class=MsoNormal> if
(TargetRegisterInfo::isPhysicalRegister(Reg) ?<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal> LivePhysRegs[Reg] :
!MRI->use_nodbg_empty(Reg)) {<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal> // This def has a non-debug
use. Don't delete the instruction!<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal> return false;<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>Returning false from MRI->use_nodbg_empty means the instruction
has a use, and it is not deleted. That's what's supposed to happen.<o:p></o:p></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
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