/* Dead-code elimination pass for the GNU compiler.
- Copyright (C) 2000, 2001 Free Software Foundation, Inc.
+ Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc.
Written by Jeffrey D. Oldham <oldham@codesourcery.com>.
-This file is part of GNU CC.
+This file is part of GCC.
-GNU CC is free software; you can redistribute it and/or modify it
-under the terms of the GNU General Public License as published by the
-Free Software Foundation; either version 2, or (at your option) any
-later version.
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 2, or (at your option) any later
+version.
-GNU CC is distributed in the hope that it will be useful, but WITHOUT
-ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License
-along with GNU CC; see the file COPYING. If not, write to the Free
+along with GCC; see the file COPYING. If not, write to the Free
Software Foundation, 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA. */
rtx dest;
void *data;
{
- int *inherently_necessary_set_p = (int *)data;
+ int *inherently_necessary_set_p = (int *) data;
while (GET_CODE (dest) == SUBREG
|| GET_CODE (dest) == STRICT_LOW_PART
switch (GET_CODE (x))
{
case CALL_INSN:
+ case BARRIER:
+ case PREFETCH:
return !0;
case CODE_LABEL:
case NOTE:
- case BARRIER:
return 0;
- break;
case JUMP_INSN:
return JUMP_TABLE_DATA_P (x) || computed_jump_p (x) != 0;
- break;
case INSN:
{
int inherently_necessary_set = 0;
}
default:
/* Found an impossible insn type. */
- abort();
+ abort ();
break;
}
}
delete_insn_bb (insn)
rtx insn;
{
- basic_block bb;
if (!insn)
abort ();
if (! INSN_P (insn))
return;
- bb = BLOCK_FOR_INSN (insn);
- if (!bb)
- abort ();
- if (bb->head == bb->end)
- {
- /* Delete the insn by converting it to a note. */
- PUT_CODE (insn, NOTE);
- NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
- return;
- }
- else if (insn == bb->head)
- bb->head = NEXT_INSN (insn);
- else if (insn == bb->end)
- bb->end = PREV_INSN (insn);
delete_insn (insn);
}
\f
for (i = 0; i < n_basic_blocks; ++i)
if (pdom[i] == INVALID_BLOCK)
pdom[i] = EXIT_BLOCK;
- el = create_edge_list();
+ el = create_edge_list ();
find_all_control_dependences (el, pdom, cdbte);
/* Find inherently necessary instructions. */
{
if (any_condjump_p (insn))
{
- /* Convert unnecessary conditional insn to an unconditional
- jump to immediate postdominator block. */
- rtx old_label = JUMP_LABEL (insn);
- int pdom_block_number =
- find_pdom (pdom, BLOCK_FOR_INSN (insn))->index;
-
- /* Prevent the conditional jump's label from being deleted so
- we do not have to modify the basic block structure. */
- ++LABEL_NUSES (old_label);
-
- if (pdom_block_number != EXIT_BLOCK
- && pdom_block_number != INVALID_BLOCK)
+ basic_block bb = BLOCK_FOR_INSN (insn);
+ basic_block pdom_bb = find_pdom (pdom, bb);
+ rtx lbl;
+ edge e;
+
+ /* Egad. The immediate post dominator is the exit block. We
+ would like to optimize this conditional jump to jump directly
+ to the exit block. That can be difficult as we may not have
+ a suitable CODE_LABEL that allows us to fall unmolested into
+ the exit block.
+
+ So, we just delete the conditional branch by turning it into
+ a deleted note. That is safe, but just not as optimal as
+ it could be. */
+ if (pdom_bb == EXIT_BLOCK_PTR)
{
- rtx lbl = find_block_label (BASIC_BLOCK (pdom_block_number));
- rtx new_jump = emit_jump_insn_before (gen_jump (lbl), insn);
+ /* Since we're going to just delete the branch, we need
+ look at all the edges and remove all those which are not
+ a fallthru edge. */
+ e = bb->succ;
+ while (e)
+ {
+ edge temp = e;
+
+ e = e->succ_next;
+ if ((temp->flags & EDGE_FALLTHRU) == 0)
+ {
+ /* We've found a non-fallthru edge, find any PHI nodes
+ at the target and clean them up. */
+ if (temp->dest != EXIT_BLOCK_PTR)
+ {
+ rtx insn
+ = first_insn_after_basic_block_note (temp->dest);
+
+ while (PHI_NODE_P (insn))
+ {
+ remove_phi_alternative (PATTERN (insn), temp->src);
+ insn = NEXT_INSN (insn);
+ }
+ }
+
+ remove_edge (temp);
+ }
+ }
+
+ /* Now "delete" the conditional jump. */
+ PUT_CODE (insn, NOTE);
+ NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
+ continue;
+ }
- /* Let jump know that label is in use. */
- JUMP_LABEL (new_jump) = lbl;
- ++LABEL_NUSES (lbl);
+ /* We've found a conditional branch that is unnecessary.
+
+ First, remove all outgoing edges from this block, updating
+ PHI nodes as appropriate. */
+ e = bb->succ;
+ while (e)
+ {
+ edge temp = e;
- delete_insn_bb (insn);
+ e = e->succ_next;
- /* A conditional branch is unnecessary if and only if any
- block control-dependent on it is unnecessary. Thus,
- any phi nodes in these unnecessary blocks are also
- removed and these nodes need not be updated. */
+ if (temp->flags & EDGE_ABNORMAL)
+ continue;
- /* A barrier must follow any unconditional jump. Barriers
- are not in basic blocks so this must occur after
- deleting the conditional jump. */
- emit_barrier_after (new_jump);
+ /* We found an edge that is not executable. First simplify
+ the PHI nodes in the target block. */
+ if (temp->dest != EXIT_BLOCK_PTR)
+ {
+ rtx insn = first_insn_after_basic_block_note (temp->dest);
+
+ while (PHI_NODE_P (insn))
+ {
+ remove_phi_alternative (PATTERN (insn), temp->src);
+ insn = NEXT_INSN (insn);
+ }
+ }
+
+ remove_edge (temp);
}
- else
- /* The block drops off the end of the function and the
- ending conditional jump is not needed. */
- delete_insn_bb (insn);
+
+ /* Create an edge from this block to the post dominator.
+ What about the PHI nodes at the target? */
+ make_edge (bb, pdom_bb, 0);
+
+ /* Third, transform this insn into an unconditional
+ jump to the label for the immediate postdominator. */
+ lbl = find_block_label (pdom_bb);
+ SET_SRC (PATTERN (insn)) = gen_rtx_LABEL_REF (VOIDmode, lbl);
+ INSN_CODE (insn) = -1;
+ JUMP_LABEL (insn) = lbl;
+ LABEL_NUSES (lbl)++;
+
+ /* A barrier must follow any unconditional jump. Barriers
+ are not in basic blocks so this must occur after
+ deleting the conditional jump. */
+ emit_barrier_after (insn);
}
else if (!JUMP_P (insn))
delete_insn_bb (insn);
/* Remove fake edges from the CFG. */
remove_fake_edges ();
+ /* Find any blocks with no successors and ensure they are followed
+ by a BARRIER. delete_insn has the nasty habit of deleting barriers
+ when deleting insns. */
+ for (i = 0; i < n_basic_blocks; i++)
+ {
+ basic_block bb = BASIC_BLOCK (i);
+
+ if (bb->succ == NULL)
+ {
+ rtx next = NEXT_INSN (bb->end);
+
+ if (!next || GET_CODE (next) != BARRIER)
+ emit_barrier_after (bb->end);
+ }
+ }
/* Release allocated memory. */
for (insn = get_insns (); insn != NULL_RTX; insn = NEXT_INSN (insn))
RESURRECT_INSN (insn);
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