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basic-block.h (first_insn_after_basic_block_note): Declare.

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* basic-block.h (first_insn_after_basic_block_note): Declare.
        * flow.c (first_insn_after_basic_block_note): Define.  Moved
        from...
        * ssa.c (first_insn_after_basic_block_note): Remove.
        * ssa-dce.c (find_inherently_necessary): Consider BARRIERs
        necessary.
        (ssa_eliminate_dead_code): Properly update the CFG and PHI
        nodes when we find a dead conditional branch.  Insert BARRIERs
        after any blocks with no successors, but which do not have
        any BARRIERs.

From-SVN: r43816
This commit is contained in:
Jeffrey A Law 2001-07-06 18:19:47 +00:00 committed by Jeff Law
parent 9d99ca5b1e
commit b62c888152
5 changed files with 143 additions and 58 deletions
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13
gcc/ChangeLog
View File

@ -1,3 +1,16 @@
Fri Jul 6 11:47:59 2001 Jeffrey A Law (law@cygnus.com)
* basic-block.h (first_insn_after_basic_block_note): Declare.
* flow.c (first_insn_after_basic_block_note): Define. Moved
from...
* ssa.c (first_insn_after_basic_block_note): Remove.
* ssa-dce.c (find_inherently_necessary): Consider BARRIERs
necessary.
(ssa_eliminate_dead_code): Properly update the CFG and PHI
nodes when we find a dead conditional branch. Insert BARRIERs
after any blocks with no successors, but which do not have
any BARRIERs.
2001-07-06 Zack Weinberg <zackw@stanford.edu>
* varray.c (varray_check_failed): Use internal_error.

2
gcc/basic-block.h
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@ -294,7 +294,7 @@ extern int flow_depth_first_order_compute PARAMS ((int *, int *));
extern void dump_edge_info PARAMS ((FILE *, edge, int));
extern void clear_edges PARAMS ((void));
extern void mark_critical_edges PARAMS ((void));
extern rtx first_insn_after_basic_block_note PARAMS ((basic_block));
/* Structure to hold information for each natural loop. */
struct loop

22
gcc/flow.c
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@ -1088,6 +1088,28 @@ create_basic_block (index, head, end, bb_note)
bb->aux = bb;
}
/* Return the INSN immediately following the NOTE_INSN_BASIC_BLOCK
note associated with the BLOCK. */
rtx
first_insn_after_basic_block_note (block)
basic_block block;
{
rtx insn;
/* Get the first instruction in the block. */
insn = block->head;
if (insn == NULL_RTX)
return NULL_RTX;
if (GET_CODE (insn) == CODE_LABEL)
insn = NEXT_INSN (insn);
if (!NOTE_INSN_BASIC_BLOCK_P (insn))
abort ();
return NEXT_INSN (insn);
}
/* Records the basic block struct in BB_FOR_INSN, for every instruction
indexed by INSN_UID. MAX is the size of the array. */

140
gcc/ssa-dce.c
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@ -370,17 +370,15 @@ find_inherently_necessary (x)
return !0;
else
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;
@ -626,50 +624,126 @@ ssa_eliminate_dead_code ()
{
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;
basic_block bb = BLOCK_FOR_INSN (insn);
basic_block pdom_bb = find_pdom (pdom, bb);
rtx lbl;
edge e;
/* Prevent the conditional jump's label from being deleted so
we do not have to modify the basic block structure. */
++LABEL_NUSES (old_label);
/* 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.
if (pdom_block_number != EXIT_BLOCK
&& pdom_block_number != INVALID_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;
/* Let jump know that label is in use. */
JUMP_LABEL (new_jump) = lbl;
++LABEL_NUSES (lbl);
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);
delete_insn_bb (insn);
while (PHI_NODE_P (insn))
{
remove_phi_alternative (PATTERN (insn), temp->src);
insn = NEXT_INSN (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. */
remove_edge (temp);
}
}
/* 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);
/* 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);

24
gcc/ssa.c
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@ -162,8 +162,6 @@ struct rename_context;
static inline rtx * phi_alternative
PARAMS ((rtx, int));
static rtx first_insn_after_basic_block_note
PARAMS ((basic_block));
static void compute_dominance_frontiers_1
PARAMS ((sbitmap *frontiers, int *idom, int bb, sbitmap done));
static void find_evaluations_1
@ -633,28 +631,6 @@ compute_iterated_dominance_frontiers (idfs, frontiers, evals, nregs)
}
}
/* Return the INSN immediately following the NOTE_INSN_BASIC_BLOCK
note associated with the BLOCK. */
static rtx
first_insn_after_basic_block_note (block)
basic_block block;
{
rtx insn;
/* Get the first instruction in the block. */
insn = block->head;
if (insn == NULL_RTX)
return NULL_RTX;
if (GET_CODE (insn) == CODE_LABEL)
insn = NEXT_INSN (insn);
if (!NOTE_INSN_BASIC_BLOCK_P (insn))
abort ();
return NEXT_INSN (insn);
}
/* Insert the phi nodes. */
static void