[Bug rtl-optimization/43056] New: __builtin_prefetch causes ICE: in rtl_verify_flow_info, at cfgrtl.c:2205 with -fsched2-use-superblocks

[Bug rtl-optimization/43056] New: __builtin_prefetch causes ICE: in rtl_verify_flow_info, at cfgrtl.c:2205 with -fsched2-use-superblocks

[zsojka at seznam dot cz]

Command line:
gcc -O1 -fschedule-insns2 -fsched2-use-superblocks -c testcase.c

-------- testcase.c --------
int x[1];
void foo()
{
  __builtin_prefetch(x);
}
----------------------------

Tested revisions:
trunk r156745 - crash
trunk r153685 - crash
4.4 r156256 - crash
4.4 r155365 - OK (no checking)
4.4 r149995 - crash

Output:
$ /mnt/svn/gcc-trunk/binary-156745-lto/bin/gcc -O1 -fschedule-insns2
-fsched2-use-superblocks -c testcase.c
testcase.c: In function ‘foo’:
testcase.c:5:1: error: missing barrier after block 2
testcase.c:5:1: error: return not followed by barrier
(jump_insn:TI 11 14 8 2 testcase.c:5 (return) 648 {return_internal} (nil))
testcase.c:5:1: internal compiler error: in rtl_verify_flow_info, at
cfgrtl.c:2205
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.


-- 
           Summary: __builtin_prefetch causes ICE: in rtl_verify_flow_info,
                    at cfgrtl.c:2205 with -fsched2-use-superblocks
           Product: gcc
           Version: 4.4.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: zsojka at seznam dot cz
  GCC host triplet: x86_64-pc-linux-gnu
GCC target triplet: x86_64-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43056

[Bug rtl-optimization/43056] __builtin_prefetch causes ICE: in rtl_verify_flow_info, at cfgrtl.c:2205 with -fsched2-use-superblocks

[steven at gcc dot gnu dot org]

-- 

steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-02-13 23:09:24
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43056

[Bug rtl-optimization/43056] __builtin_prefetch causes ICE: in rtl_verify_flow_info, at cfgrtl.c:2205 with -fsched2-use-superblocks

[steven at gcc dot gnu dot org]

------- Comment #1 from steven at gcc dot gnu dot org  2010-02-13 23:18 -------
Breakpoint 7, rest_of_handle_sched2 () at ../../trunk/gcc/sched-rgn.c:3534
3534          && ! maybe_skip_selective_scheduling ())
(gdb) p brief_dump_cfg(stderr)
Basic block 2 (reachable, rtl)
Predecessors:  ENTRY [100.0%]  (fallthru)
Successors:  EXIT [100.0%]


The .split4 dump (just before .sched2):
;; Function foo (foo)

    1 NOTE_INSN_DELETED 
    3 NOTE_INSN_BASIC_BLOCK
    9 NOTE_INSN_PROLOGUE_END
    2 NOTE_INSN_FUNCTION_BEG
    5 prefetch(`x',0x0,0x3)
   10 NOTE_INSN_EPILOGUE_BEG 
   11 return
i  12: barrier
    8 NOTE_INSN_DELETED

And the .sched2 dump:
changing bb of uid 13
  unscanned insn  
changing bb of uid 5
  from 2 to 3

deleting block 3
    1 NOTE_INSN_DELETED
    3 NOTE_INSN_BASIC_BLOCK
    9 NOTE_INSN_PROLOGUE_END
    2 NOTE_INSN_FUNCTION_BEG
   14 NOTE_INSN_EPILOGUE_BEG
   11 return
    8 NOTE_INSN_DELETED

What insn 13? What basic block 3?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43056

[Bug rtl-optimization/43056] __builtin_prefetch causes ICE: in rtl_verify_flow_info, at cfgrtl.c:2205 with -fsched2-use-superblocks

[steven at gcc dot gnu dot org]

------- Comment #2 from steven at gcc dot gnu dot org  2010-02-13 23:29 -------
This is a gem, the scheduler attempts to schedule the prefetch *after* the
return.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43056

[Bug rtl-optimization/43056] __builtin_prefetch causes ICE: in rtl_verify_flow_info, at cfgrtl.c:2205 with -fsched2-use-superblocks

[steven at gcc dot gnu dot org]

------- Comment #3 from steven at gcc dot gnu dot org  2010-02-14 00:07 -------
User prefetches should never be scheduled. Andreas Krebbel posted a patch
towards that (http://gcc.gnu.org/ml/gcc-patches/2009-09/msg00130.html) but he
hasn't followed up on it, so far.

Of course, in very rare corner cases, it is possible to have a non-user
prefetch and then all other code removed as dead. To handle this situation,
sched-ebb.c should not move the barrier after the jump into a new basic block.
But I don't know if this is the responsibility of the CFGRTL modification
interface, or of the user of this interface. If the latter, the following patch
would be necessary:

Index: sched-ebb.c
===================================================================
--- sched-ebb.c (revision 156750)
+++ sched-ebb.c (working copy)
@@ -174,8 +174,13 @@
          gcc_assert (NOTE_INSN_BASIC_BLOCK_P (BB_END (bb)));
        }
       else
-       /* Create an empty unreachable block after the INSN.  */
-       bb = create_basic_block (NEXT_INSN (insn), NULL_RTX, last_bb);
+       {
+         /* Create an empty unreachable block after the INSN.  */
+          rtx head = NEXT_INSN (insn);
+         while (head && BARRIER_P (head))
+           head = NEXT_INSN (head);
+         bb = create_basic_block (head, NULL_RTX, last_bb);
+       }

       /* split_edge () creates BB before E->DEST.  Keep in mind, that
         this operation extends scheduling region till the end of BB.


-- 

steven at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |krebbel at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43056