<html><head><base href="x-msg://15/"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Jun 6, 2011, at 7:07 AM, Arnaud Allard de Grandmaison wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; font-family: Optima; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div lang="EN-US" link="blue" vlink="#606420"><div class="Section1" style="page: Section1; "><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; ">Hi All,<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; "><o:p> </o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; 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.<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; "><o:p> </o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; 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.<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; "><o:p> </o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; ">I have derived from PBQPBuilder to add the MPQD constraint.<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; "><o:p> </o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; ">It happens sometimes that the code for register allocation looks like this :<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; "> ...<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; "> MPQD %vreg80, %vreg79, %vreg80; GR16:%vreg80,%vreg79<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; "> ...<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; ">Operands 0 & 2 have been coalesced and I can no longer set the constraint.<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; "><o:p> </o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; 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.<o:p></o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; "><o:p> </o:p></span></font></div><div style="margin-top: 0cm; margin-right: 0cm; margin-bottom: 0.0001pt; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman'; "><font size="2" face="Arial"><span style="font-size: 10pt; font-family: Arial; ">What would be the appropriate way to handle this case ?</span></font></div></div></div></span></blockquote><div><br></div><div>You would need to run your pass after coalescing, but before PBQP runs.</div><div><br></div><div>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.</div><div><br></div><div>/jakob</div><div><br></div></div></body></html>