'fix' for 11350 causes bootstrap hang on Darwin

[Geoff Keating <geoffk at desire dot geoffk dot org>]

Hi Jan,

This patch:

2004-01-16  Jan Hubicka  <jh@suse.cz>

        PR opt/11350
        * cfgcleanup.c (try_optimize_cfg): Suppress tablejump removal
        after reload.
        * cfgrtl.c (rtl_can_merge_blocks, cfglayout_can_merge_blocks,
        rtl_try_redirect_by_replacing_branch): Likewise.

causes bootstrap to hang on powerpc-darwin.  The sequence is:

- try_optimize_cfg sees a branch like:

(jump_insn:HI 284 735 291 26 insn-attrtab.c:99366 (parallel [
            (set (pc)
                (reg:SI 66 ctr [198]))
            (use (label_ref 285))
        ]) 515 {*rs6000.md:13804} (insn_list 735 (nil))
    (expr_list:REG_DEAD (reg:SI 66 ctr [198])
        (nil)))

which is the remains of a tablejump insn.  It runs this chunk of code:

              /* If B has a single outgoing edge, but uses a
                 non-trivial jump instruction without side-effects, we
                 can either delete the jump entirely, or replace it
                 with a simple unconditional jump.  Use
                 redirect_edge_and_branch to do the dirty work.  */
              if (b->succ
                  && ! b->succ->succ_next
                  && b->succ->dest != EXIT_BLOCK_PTR
                  && onlyjump_p (BB_END (b))
                  && redirect_edge_and_branch (b->succ,
                 b->succ->dest))
                {
                  update_forwarder_flag (b);
                  changed_here = true;
                }

- rtl_redirect_edge_and_branch calls try_redirect_by_replacing_jump
- try_redirect_by_replacing_jump returns false because
  this is (was) a tablejump and reload_completed is set
- rtl_redirect_edge_and_branch then enters this code:

2444      if (e->dest == dest)
2445        return true;

and since this is true (because it was called with 'dest' set to
b->succ->dest and 'e' set to b->succ), it'll return true without doing
anything.

I'm now testing this patch, and will commit if bootstrap & testrun
succeeds (I presume that a testcase was added for 11350, since
there's one in the bug report).

2004-01-16  Geoffrey Keating  <geoffk@apple.com>

        * cfgrtl.c (try_redirect_by_replacing_jump): Optimize tablejumps
        even after reload, just don't remove the actual jump tables.

*** cfgrtl.c.~1.103.~   Fri Jan 16 19:07:19 2004
--- cfgrtl.c    Fri Jan 16 22:15:03 2004
***************
*** 703,709 ****

    if (tmp || !onlyjump_p (insn))
      return false;
!   if ((!optimize || reload_completed) && tablejump_p (insn, NULL, NULL))
      return false;

    /* Avoid removing branch with side effects.  */
--- 703,709 ----

    if (tmp || !onlyjump_p (insn))
      return false;
!   if ((!optimize || flow2_completed) && tablejump_p (insn, NULL, NULL))
      return false;

    /* Avoid removing branch with side effects.  */
***************
*** 793,799 ****
        /* Recognize a tablejump that we are converting to a
         simple jump and remove its associated CODE_LABEL
         and ADDR_VEC or ADDR_DIFF_VEC.  */
!       if (tablejump_p (insn, &label, &table))
        delete_insn_chain (label, table);

        barrier = next_nonnote_insn (BB_END (src));
--- 793,799 ----
        /* Recognize a tablejump that we are converting to a
         simple jump and remove its associated CODE_LABEL
         and ADDR_VEC or ADDR_DIFF_VEC.  */
!       if (! reload_completed && tablejump_p (insn, &label, &table))
        delete_insn_chain (label, table);

        barrier = next_nonnote_insn (BB_END (src));


-- 
- Geoffrey Keating <geoffk@geoffk.org>