/* Dead-code elimination pass for the GNU compiler.
- Copyright (C) 2000 Free Software Foundation, Inc.
+ Copyright (C) 2000, 2001 Free Software Foundation, Inc.
Written by Jeffrey D. Oldham <oldham@codesourcery.com>.
This file is part of GNU CC.
The last step can require adding labels, deleting insns, and
modifying basic block structures. Some conditional jumps may be
converted to unconditional jumps so the control-flow graph may be
- out-of-date.
+ out-of-date.
Edges from some infinite loops to the exit block can be added to
the control-flow graph, but will be removed after this pass is
if (INDEX_EDGE_PRED_BB (el, edge_index) == EXIT_BLOCK_PTR)
abort ();
- ending_block =
- (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR)
- ? BASIC_BLOCK (0)
+ ending_block =
+ (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR)
+ ? BASIC_BLOCK (0)
: find_pdom (pdom, INDEX_EDGE_PRED_BB (el, edge_index));
for (current_block = INDEX_EDGE_SUCC_BB (el, edge_index);
{
case CLOBBER:
/* Do not traverse the rest of the clobber. */
- return -1;
+ return -1;
break;
case PC:
return 0;
/* Called via note_stores for each store in an insn. Note whether
or not a particular store is inherently necessary. Store a
- nonzero value in inherently_necessary_p if such a storeis found. */
-
+ nonzero value in inherently_necessary_p if such a store is found. */
+
static void
note_inherently_necessary_set (dest, set, data)
- rtx set;
+ rtx set ATTRIBUTE_UNUSED;
rtx dest;
void *data;
{
find_inherently_necessary (x)
rtx x;
{
- rtx pattern;
if (x == NULL_RTX)
return 0;
else if (inherently_necessary_register (x))
switch (GET_CODE (x))
{
case CALL_INSN:
+ case BARRIER:
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;
{
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);
-
- /* Let jump know that label is in use. */
- JUMP_LABEL (new_jump) = lbl;
- ++LABEL_NUSES (lbl);
-
- delete_insn_bb (insn);
-
- /* 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. */
-
- /* 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);
+ /* 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;
}
- else
- /* The block drops off the end of the function and the
- ending conditional jump is not needed. */
- delete_insn_bb (insn);
+
+ /* 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;
+
+ e = e->succ_next;
+
+ if (temp->flags & EDGE_ABNORMAL)
+ continue;
+
+ /* 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);
+ }
+
+ /* Create an edge from this block to the post dominator.
+ What about the PHI nodes at the target? */
+ make_edge (NULL, 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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