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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Thanks Jakob,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I will try that.<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=2 color=navy face="Courier New"><span lang=FR
style='font-size:10.0pt;font-family:"Courier New";color:navy'>-- <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face="Courier New"><span lang=FR
style='font-size:10.0pt;font-family:"Courier New";color:navy'>Arnaud de
Grandmaison <o:p></o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Jakob Stoklund
Olesen [mailto:stoklund@2pi.dk] <br>
<b><span style='font-weight:bold'>Sent:</span></b> Monday, June 06, 2011 4:24
PM<br>
<b><span style='font-weight:bold'>To:</span></b> Arnaud Allard de Grandmaison<br>
<b><span style='font-weight:bold'>Cc:</span></b> <st1:PersonName w:st="on">llvmdev@cs.uiuc.edu</st1:PersonName><br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [LLVMdev] PBQP &
register pairing</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>On Jun 6, 2011, at 7:07 AM, Arnaud Allard de Grandmaison wrote:<o:p></o:p></span></font></p>
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<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Hi All,<u1:p></u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>My target has some instructions requiring register pairs. I
decided to give a try to the PBQP allocator : it is working fine in 99% of the
cases, but I am stumbling on the following issue.<u1:p></u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Instruction ‘MPQD’ takes 3 register operands
inputs, with the constraint that operands 0 and 2 must be consecutive
registers. Operand 1 has no particular constraint. It has no output register.
So we have something like MPQD R_n, R_x, R_n+1.<u1:p></u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I have derived from PBQPBuilder to add the MPQD constraint.<u1:p></u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>It happens sometimes that the code for register allocation
looks like this :<u1:p></u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'> ...<u1:p></u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'> MPQD %vreg80, %vreg79, %vreg80; GR16:%vreg80,%vreg79<u1:p></u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'> ...<u1:p></u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Operands 0 & 2 have been coalesced and I can no
longer set the constraint.<u1:p></u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I tried to add a pass right before register allocation, to
catch those case and insert a copy for operand 2, but the copy gets coalesced
away.<u1:p></u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><u1:p> </u1:p></span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>What would be the appropriate way to handle this case ?</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>You would need to run your pass after coalescing, but before PBQP runs.<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>There is currently no standard hook for inserting passes in that
location, but it may make sense for PBQP to offer such a hook since it can
support many strange constraints.<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>/jakob<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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