------- Comment #9 from law at redhat dot com 2010-01-29 11:01 ------- At some point IRA's handling of earlyclobber constraints improved enough to get the conflicts right in this PR. Unfortunately, that is not sufficient to generate good code.
If we compile the testcase on i686-pc-linux-gnu with -O2 -fomit-frame-pointer, we should be able to allocate hard regs for all the allocnos *and* do so without generating any reloads. Unfortunately, IRA makes poor register selections which ultimately lead to reloading. Pass 0 for finding pseudo/allocno costs a0 (r68,l0) best AREG, cover GENERAL_REGS a4 (r67,l0) best Q_REGS, cover GENERAL_REGS a3 (r66,l0) best GENERAL_REGS, cover GENERAL_REGS a1 (r65,l0) best GENERAL_REGS, cover GENERAL_REGS a5 (r64,l0) best GENERAL_REGS, cover GENERAL_REGS a2 (r63,l0) best GENERAL_REGS, cover GENERAL_REGS a7 (r59,l0) best GENERAL_REGS, cover GENERAL_REGS a6 (r58,l0) best GENERAL_REGS, cover GENERAL_REGS a0(r68,l0) costs: AREG:-1000,-1000 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:6000 a1(r65,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:7000 a2(r63,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:28000 a3(r66,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:16000 a4(r67,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:4000,4000 DIREG:4000,4000 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:4000,4000 GENERAL_REGS:4000,4000 MEM:16000 a5(r64,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:4000 a6(r58,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:3000 a7(r59,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:3000 Pass 1 for finding pseudo/allocno costs r68: preferred AREG, alternative GENERAL_REGS, cover GENERAL_REGS r67: preferred Q_REGS, alternative GENERAL_REGS, cover GENERAL_REGS r66: preferred GENERAL_REGS, alternative NO_REGS, cover GENERAL_REGS r65: preferred GENERAL_REGS, alternative NO_REGS, cover GENERAL_REGS r64: preferred GENERAL_REGS, alternative NO_REGS, cover GENERAL_REGS r63: preferred GENERAL_REGS, alternative NO_REGS, cover GENERAL_REGS r59: preferred GENERAL_REGS, alternative NO_REGS, cover GENERAL_REGS r58: preferred GENERAL_REGS, alternative NO_REGS, cover GENERAL_REGS a0(r68,l0) costs: AREG:-1000,-1000 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:6000 a1(r65,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:7000 a2(r63,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:28000 a3(r66,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:16000 a4(r67,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:4000,4000 DIREG:4000,4000 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:4000,4000 GENERAL_REGS:4000,4000 MEM:16000 a5(r64,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:4000 a6(r58,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:3000 a7(r59,l0) costs: AREG:0,0 DREG:0,0 CREG:0,0 BREG:0,0 SIREG:0,0 DIREG:0,0 AD_REGS:0,0 CLOBBERED_REGS:0,0 Q_REGS:0,0 NON_Q_REGS:0,0 GENERAL_REGS:0,0 MEM:3000 That looks fairly reasonable. pseudo 68 is the return value, so assigning it into ax is a win. r67 wants Q_REGS so assigning it to SI, DI, or NON_Q has a cost. ;; a0(r68,l0) conflicts: ;; total conflict hard regs: ;; conflict hard regs: ;; a1(r65,l0) conflicts: a3(r66,l0) a2(r63,l0) a4(r67,l0) a5(r64,l0) ;; total conflict hard regs: 1 2 ;; conflict hard regs: 1 2 ;; a2(r63,l0) conflicts: a1(r65,l0) a3(r66,l0) a4(r67,l0) a5(r64,l0) a6(r58,l0) a7(r59,l0) ;; total conflict hard regs: 1 2 ;; conflict hard regs: 1 2 ;; a3(r66,l0) conflicts: a1(r65,l0) a2(r63,l0) a4(r67,l0) a5(r64,l0) a6(r58,l0) ;; total conflict hard regs: 1 2 ;; conflict hard regs: 1 2 ;; a4(r67,l0) conflicts: a1(r65,l0) a3(r66,l0) a2(r63,l0) a5(r64,l0) ;; total conflict hard regs: 1 2 ;; conflict hard regs: 1 2 ;; a5(r64,l0) conflicts: a1(r65,l0) a3(r66,l0) a2(r63,l0) a4(r67,l0) ;; total conflict hard regs: 1 2 ;; conflict hard regs: 1 2 ;; a6(r58,l0) conflicts: a3(r66,l0) a2(r63,l0) a7(r59,l0) ;; total conflict hard regs: ;; conflict hard regs: ;; a7(r59,l0) conflicts: a2(r63,l0) a6(r58,l0) ;; total conflict hard regs: ;; conflict hard regs: cp0:a3(r66)<->a7(r59)@1000:move cp1:a4(r67)<->a6(r58)@1000:move cp2:a0(r68)<->a1(r65)@125:shuffle The r65/r68 copy will cause IRA to want to use ax for r65 and as a result will increase the cost of ax for every pseudo which conflicts with r65 (r63, r64, r66, r67). So far, so good. The problem is I don't see where we increase the cost of Q_REGS for pseudos which conflict with r67. So when we color: Pushing a7(r59,l0) Pushing a6(r58,l0) Pushing a0(r68,l0) Pushing a3(r66,l0)(potential spill: pri=2285, cost=16000) Pushing a4(r67,l0)(potential spill: pri=2666, cost=16000) Pushing a1(r65,l0) Pushing a5(r64,l0) Pushing a2(r63,l0) Popping a2(r63,l0) -- assign reg 3 Popping a5(r64,l0) -- assign reg 4 Popping a1(r65,l0) -- assign reg 0 Popping a4(r67,l0) -- assign reg 5 Popping a3(r66,l0) -- assign reg 6 Popping a0(r68,l0) -- assign reg 0 Popping a6(r58,l0) -- assign reg 5 Popping a7(r59,l0) -- assign reg 6 We've assigned r63 into bx and thus r67 can't be assigned into bx. We ultimately assign r67 into di. That in turn causes r65 to get spilled during reload so that r67 can be reloaded into a Q_REGs and ultimately we generate crappy code. It seems to me we ought to have code which increases the cost for Q_REGS for pseudos conflicting with r67, but I can't seem to find it. FWIW, if I manually increase the cost of Q_REGS for pseudos r63, r64, r65, r66) I get the following coloring: Pushing a7(r59,l0) Pushing a6(r58,l0) Pushing a0(r68,l0) Pushing a3(r66,l0)(potential spill: pri=2285, cost=16000) Pushing a4(r67,l0)(potential spill: pri=2666, cost=16000) Pushing a1(r65,l0) Pushing a5(r64,l0) Pushing a2(r63,l0) Popping a2(r63,l0) -- assign reg 4 Popping a5(r64,l0) -- assign reg 5 Popping a1(r65,l0) -- assign reg 0 Popping a4(r67,l0) -- assign reg 3 Popping a3(r66,l0) -- assign reg 6 Popping a0(r68,l0) -- assign reg 0 Popping a6(r58,l0) -- assign reg 3 Popping a7(r59,l0) -- assign reg 6 Which is a perfect allocation requiring no reloads. -- law at redhat dot com changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Ever Confirmed|0 |1 Last reconfirmed|0000-00-00 00:00:00 |2010-01-29 11:01:15 date| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36539