------- Additional Comments From amylaar at gcc dot gnu dot org 2004-10-15 15:49
-------
Looking closer, I see that sched-deps.c already has code to keep branches, calls
and USEs at the end of the last basic block.
The problem is that lcm.c:optimize_mode_switching has put some
instructions after the USE before sched1 is run.
In this code:
/* Split the edge from the entry block and the fallthrough edge to the
exit block, so that we can note that there NORMAL_MODE is supplied /
required. */
edge eg;
edge_iterator ei;
post_entry = split_edge (EDGE_SUCC (ENTRY_BLOCK_PTR, 0));
/* The only non-call predecessor at this stage is a block with a
fallthrough edge; there can be at most one, but there could be
none at all, e.g. when exit is called. */
pre_exit = 0;
FOR_EACH_EDGE (eg, ei, EXIT_BLOCK_PTR->preds)
if (eg->flags & EDGE_FALLTHRU)
{
regset live_at_end = eg->src->global_live_at_end;
gcc_assert (!pre_exit);
pre_exit = split_edge (eg);
COPY_REG_SET (pre_exit->global_live_at_start, live_at_end);
COPY_REG_SET (pre_exit->global_live_at_end, live_at_end);
break;
}
}
We create a new block at the end to put the final mode switch into.
If the fall-through predecessor of the exit block is the only predecessor
of the exit block, and it ends with a USE, then instead of split_edge
we should use split_block, to place the USE and the preceding copy from
the result to the return value register into the new block.
I would write a patch for this, but the copyright assignment for STM is not
finished yet.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16482
