[Bug rtl-optimization/56023] [4.6 Regression]: [alpha] -fcompare-debug failure due to sched1 pass

["ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

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.