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Arnaud,<div> another way to look at it, if the description of your register sets includes "pairs",</div><div>is that your assembly language syntax for MPQD is redundant, operand-2 is the second</div><div>half of the register-pair in operand-0, so an alternative is to let llvm think this is a two</div><div>operand instruction (one of them being a pair) rather than a three operand instruction.</div><div><br></div><div>even if you are not currently defining pairs in your register definitions, it might be less work</div><div>to do that than to write and add an extra new pass. Many many target machines have some</div><div>notion of register pairs, so it should not be too hard to find examples of how to do this.</div><div><br></div><div>YMMV,</div><div>-Peter Lawrence.</div><div><br></div><div><br></div><div><br><div><div>On Jun 6, 2011, at 10:00 AM, <a href="mailto:llvmdev-request@cs.uiuc.edu">llvmdev-request@cs.uiuc.edu</a> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Monaco; min-height: 16px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco">Hi All,</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Monaco; min-height: 16px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco">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.</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Monaco; min-height: 16px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco">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.</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Monaco; min-height: 16px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco">I have derived from PBQPBuilder to add the MPQD constraint.</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Monaco; min-height: 16px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco">It happens sometimes that the code for register allocation looks like this :</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco"><span class="Apple-converted-space"> </span>...</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco"><span class="Apple-converted-space"> </span>MPQD %vreg80, %vreg79, %vreg80; GR16:%vreg80,%vreg79</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco"><span class="Apple-converted-space"> </span>...</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco">Operands<span class="Apple-converted-space"> </span>0 & 2 have been coalesced and I can no longer set the constraint.</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Monaco; min-height: 16px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco">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.</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Monaco; min-height: 16px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco">What would be the appropriate way to handle this case ?</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Monaco; min-height: 16px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco">Thanks,</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco">--</font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Monaco" size="3" style="font: 12.0px Monaco">Arnaud de Grandmaison</font></div> </blockquote></div><br></div></body></html>