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<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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<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>
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</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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<p class=MsoNormal>On Apr 14, 2010, at 1:55 PMPDT, Villmow, Micah wrote:<o:p></o:p></p>
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<p class=MsoNormal><br>
<br>
<o:p></o:p></p>
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<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>
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<p class=MsoNormal>Huh? The code is<o:p></o:p></p>
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<p class=MsoNormal> if
(TargetRegisterInfo::isPhysicalRegister(Reg) ?<o:p></o:p></p>
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<p class=MsoNormal> LivePhysRegs[Reg] :
!MRI->use_nodbg_empty(Reg)) {<o:p></o:p></p>
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<div>
<p class=MsoNormal> // This def has a non-debug
use. Don't delete the instruction!<o:p></o:p></p>
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<p class=MsoNormal> return false;<o:p></o:p></p>
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<p class=MsoNormal><o:p> </o:p></p>
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<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>
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<p class=MsoNormal><o:p> </o:p></p>
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