http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56023
--- Comment #5 from Uros Bizjak <ubizjak at gmail dot com> 2013-01-18 17:38:23
UTC ---
Bookkeeping seems somehow broken to me in sched1 pass:
-O2 -fcompare-debug -fdump-rtl-sched1-slim -S:
_.c.190r.sched1:
;; ======================================================
;; -- basic block 5 from 48 to 49 -- before reload
;; ======================================================
changing bb of uid 64
from 8 to 5
;; 0--> 64 r137=zxn(r76#0)
;; 1--> 48 r111=r90==0x20
changing bb of uid 65
from 8 to 5
;; 2--> 65 r119=r95+r137
;; 2--> 49 pc={(r111==0)?L59:pc}
;; Ready list (final):
;; total time = 2
;; new head = 48
;; new tail = 49
New head is 64, *not* 48.
And here comes the difference:
_.c.190r.sched1:
;; ======================================================
;; -- basic block 10 from 94 to 94 -- before reload
;; ======================================================
changing bb of uid 25
from 4 to 10
;; 1--> 25 r100=zxn(r75#0)
;; 1--> 94 pc={(r90!=0)?L93:pc}
;; Ready list (final): 39/b6:18 37/b6:17
;; total time = 1
;; new head = 94
;; new tail = 94
Again wrong head w/o -g.
_.c.gk.190r.sched1
;; ======================================================
;; -- basic block 10 from 99 to 102 -- before reload
;; ======================================================
;; 0--> 99: debug i => r76#0
;; 0--> 100: debug x => r75#0
changing bb of uid 29
from 4 to 10
;; 1--> 29 r100=zxn(r75#0)
;; 1--> 102 pc={(r90!=0)?L101:pc}
;; Ready list (final): 43/b6:20 41/b6:19
;; total time = 1
;; new head = 99
;; new tail = 102
Here we account debug instructions as head. I suspect that this is the cause of
the difference in a follow-up block, where we schedule in a different ways:
_.c.190r.sched1:
;; ======================================================
;; -- basic block 4 from 26 to 40 -- before reload
;; ======================================================
;; 1--> 26 r102=r100==0x1
;; 2--> 31 r105=ltu(r138,r137)
;; 3--> 27 r101=r102==0
;; 4--> 37 r92=sxn(r92#0+0x1)
;; 5--> 35 r79=r101&r105
;; 6--> 39 r76=sxn(r76#0+0x1)
;; 6--> 40 pc={(r79!=0)?L97:pc}
_.c.gk.190r.sched1
;; ======================================================
;; -- basic block 4 from 30 to 44 -- before reload
;; ======================================================
;; 0--> 43 r76=sxn(r76#0+0x1)
;; 1--> 30 r102=r100==0x1
;; 2--> 35 r105=ltu(r138,r137)
;; 3--> 31 r101=r102==0
;; 4--> 41 r92=sxn(r92#0+0x1)
;; 5--> 39 r79=r101&r105
;; 6--> 44 pc={(r79!=0)?L105:pc}
In the later dump, (insn 43) was scheduled above all others.
