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From: "law at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/36539] IRA doesn't account for earlyclobber asm conflicts
Date: Fri, 29 Jan 2010 11:01:00 -0000 [thread overview]
Message-ID: <20100129110115.27185.qmail@sourceware.org> (raw)
In-Reply-To: <bug-36539-10175@http.gcc.gnu.org/bugzilla/>
------- 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
next prev parent reply other threads:[~2010-01-29 11:01 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-06-14 6:48 [Bug target/36539] New: [4.4 regression] IRA doesn't allocate asm output being returned to eax astrange at ithinksw dot com
2008-06-14 6:49 ` [Bug target/36539] " astrange at ithinksw dot com
2008-06-14 6:53 ` [Bug target/36539] " pinskia at gcc dot gnu dot org
2008-08-27 4:42 ` [Bug target/36539] [4.4 regression] " astrange at ithinksw dot com
2008-08-29 4:43 ` pinskia at gcc dot gnu dot org
2008-08-29 19:19 ` vmakarov at redhat dot com
2008-09-04 4:04 ` astrange at ithinksw dot com
2008-09-09 20:15 ` [Bug target/36539] " jsm28 at gcc dot gnu dot org
2008-09-18 1:31 ` [Bug target/36539] IRA+i386 " astrange at ithinksw dot com
2008-12-05 20:09 ` astrange at ithinksw dot com
2010-01-29 11:01 ` law at redhat dot com [this message]
2010-01-29 20:34 ` [Bug target/36539] Poor register allocation from IRA vmakarov at redhat dot com
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