A problem with the loop structure

["Vladimir Yanovsky" <volodyan at gmail dot com>]

Hi all,

I will greatly appreciate any suggestions regarding the following
problem I have with the loop structure. I am working on Swing Modulo
Scheduling with Sony SDK for SPU (based on gcc 4.1.1). Below there are
3 observation describing the problem.

Thanks a lot,
Vladimir

1. The problem was unveiled by compiling a testcase with dump turned
on. The compilation failed while calling function get_loop_body from
flow_loop_dump on the following assert :

 else if (loop->latch != loop->header)
   {
     tv = dfs_enumerate_from (loop->latch, 1, glb_enum_p,
                              tovisit + 1, loop->num_nodes - 1,
                              loop->header) + 1;


 gcc_assert (tv == loop->num_nodes);

The compilation exits successfully if compiled without enabling the dump.

2. SMS pass contained a single call to loop_version on the loop to be
SMSed. This happened before any SMS related stuff was done. Trying to
call verify_loop_structure(loops) just after the call to loop_version
failed on the same assert in get_loop_body as in (1). The loop on
which we fail is neither the versioned loop nor the new loop. Below
there are dumps to verify_loop_structure called from different places
in loop_version:

(gdb) n
1466      first_head = entry->dest;
(gdb) p verify_loop_structure(loops)
$12 = void
(gdb) n
1469      if (!cfg_hook_duplicate_loop_to_header_edge (loop, entry, loops, 1,
(gdb) p verify_loop_structure(loops)
$13 = void
(gdb) n
1475      second_head = entry->dest;
(gdb) p verify_loop_structure(loops)
bmark_lite.c: In function 't_run_test':
bmark_lite.c:1225: error: loop 7's header does not have exactly 2 entries

Breakpoint 1, fancy_abort (
   file=0x884008 "/Develop/sony/build/toolchain/gcc/gcc/cfgloop.c", line=1277,
   function=0x8841d0 "verify_loop_structure")
   at /Develop/sony/build/toolchain/gcc/gcc/diagnostic.c:602
602       internal_error ("in %s, at %s:%d", function, trim_filename
(file), line);



3.  At the very beginning of the SMS pass we build the loop structure
using build_loops_structure defined in modulo-sched.c. Just after the
call I tried to print in gdb the loop on which we failed in
get_loop_body. This failed as well

(gdb)  p print_loop(dumpfile, 0xbabe20, 0)
No symbol "dumpfile" in current context.
(gdb)  p print_loop(stdout, 0xbabe20, 0)
loop_0
{
}
$1 = void
(gdb)  p print_loop(stdout, 0xd42e20, 0)
loop_7
{
 bb_21 (preds = {bb_256 }, succs = {bb_23 bb_22 })
 {
 <L21>:;
   matrixA.770 = matrixA;
   temp.801 = *(matrixA.770 + (varsize * *) ivtmp.701 * 4B);
   temp.874 = temp.801 + pretmp.130;
   sum1_lsm.411 = *temp.874;
   col1_lsm.839 = (int) ivtmp.701;
   col1_lsm.837 = 0;
   if (col1_lsm.839 > 0) goto <L628>; else (void) 0;

 }
 bb_23 (preds = {bb_21 }, succs = {bb_262 })
 {
 <L628>:;
   ivtmp.694 = 0;

 }
 bb_262 (preds = {bb_23 }, succs = {bb_264 bb_263 })
 {

Breakpoint 1, fancy_abort (
   file=0x86e980 "/Develop/sony/build/toolchain/gcc/gcc/tree-flow-inline.h",
   line=722, function=0x86e9b9 "bsi_start")
   at /Develop/sony/build/toolchain/gcc/gcc/diagnostic.c:602
602       internal_error ("in %s, at %s:%d", function, trim_filename
(file), line);


The failure was on the assert in line 722(please find below):

(gdb) up
#1  0x0000000000469d80 in bsi_start (bb=0x2aaaaebc0100)
   at /Develop/sony/build/toolchain/gcc/gcc/tree-flow-inline.h:722
722           gcc_assert (bb->index < 0);
(gdb) l
717       block_stmt_iterator bsi;
718       if (bb->stmt_list)
719         bsi.tsi = tsi_start (bb->stmt_list);
720       else
721         {
722           gcc_assert (bb->index < 0);
723           bsi.tsi.ptr = NULL;
724           bsi.tsi.container = NULL;
725         }
726       bsi.bb = bb;
(gdb)