Skip to content

R
riscv-gcc-1
Commit f7d0c571 by Zhenqiang Chen Committed by Bin Cheng
Options

re PR middle-end/54364 (Tail call jumps not threaded) 

	PR middle-end/54364
	* bb-reorder.c (connect_better_edge_p): New added.
	(find_traces_1_round): When optimizing for size, ignore edge frequency
	and probability, and handle all in one round.
	(bb_to_key): Use bb->index as key when optimizing for size.
	(better_edge_p): The bb with smaller index is better when optimizing
	for size.
	(connect_traces): When optimizing for size, connect block n with
	block n + 1; connect trace m with trace m + 1 if falling through.
	(gate_handle_reorder_blocks): Enable bbro when optimizing for -Os.

From-SVN: r191462
parent 878b569c
Showing with 189 additions and 29 deletions
gcc/ChangeLog
2012-09-19 Zhenqiang Chen <zhenqiang.chen@arm.com>
PR middle-end/54364
* bb-reorder.c (connect_better_edge_p): New added.
(find_traces_1_round): When optimizing for size, ignore edge frequency
and probability, and handle all in one round.
(bb_to_key): Use bb->index as key when optimizing for size.
(better_edge_p): The bb with smaller index is better when optimizing
for size.
(connect_traces): When optimizing for size, connect block n with
block n + 1; connect trace m with trace m + 1 if falling through.
(gate_handle_reorder_blocks): Enable bbro when optimizing for -Os.
2012-09-19 Bin Cheng <bin.cheng@arm.com>
* fold-const.c (fold_truth_andor): Remove duplicated check on
......
gcc/bb-reorder.c
......@@ -56,6 +56,20 @@
The rest of traces are simply connected so there will be a jump to the
beginning of the rest of traces.
The above description is for the full algorithm, which is used when the
function is optimized for speed. When the function is optimized for size,
in order to reduce long jumps and connect more fallthru edges, the
algorithm is modified as follows:
(1) Break long traces to short ones. A trace is broken at a block that has
multiple predecessors/ successors during trace discovery. When connecting
traces, only connect Trace n with Trace n + 1. This change reduces most
long jumps compared with the above algorithm.
(2) Ignore the edge probability and frequency for fallthru edges.
(3) Keep the original order of blocks when there is no chance to fall
through. We rely on the results of cfg_cleanup.
To implement the change for code size optimization, block's index is
selected as the key and all traces are found in one round.
References:
......@@ -181,6 +195,8 @@ static basic_block copy_bb (basic_block, edge, basic_block, int);
static fibheapkey_t bb_to_key (basic_block);
static bool better_edge_p (const_basic_block, const_edge, int, int, int, int,
const_edge);
static bool connect_better_edge_p (const_edge, bool, int, const_edge,
struct trace *);
static void connect_traces (int, struct trace *);
static bool copy_bb_p (const_basic_block, int);
static bool push_to_next_round_p (const_basic_block, int, int, int, gcov_type);
......@@ -440,6 +456,7 @@ find_traces_1_round (int branch_th, int exec_th, gcov_type count_th,
/* Heap for discarded basic blocks which are possible starting points for
the next round. */
fibheap_t new_heap = fibheap_new ();
bool for_size = optimize_function_for_size_p (cfun);
while (!fibheap_empty (*heap))
{
......@@ -459,10 +476,11 @@ find_traces_1_round (int branch_th, int exec_th, gcov_type count_th,
/* If the BB's frequency is too low, send BB to the next round. When
partitioning hot/cold blocks into separate sections, make sure all
the cold blocks (and ONLY the cold blocks) go into the (extra) final
round. */
round. When optimizing for size, do not push to next round. */
if (push_to_next_round_p (bb, round, number_of_rounds, exec_th,
count_th))
if (!for_size
&& push_to_next_round_p (bb, round, number_of_rounds, exec_th,
count_th))
{
int key = bb_to_key (bb);
bbd[bb->index].heap = new_heap;
......@@ -533,10 +551,11 @@ find_traces_1_round (int branch_th, int exec_th, gcov_type count_th,
}
/* Edge that cannot be fallthru or improbable or infrequent
successor (i.e. it is unsuitable successor). */
successor (i.e. it is unsuitable successor). When optimizing
for size, ignore the probability and frequency. */
if (!(e->flags & EDGE_CAN_FALLTHRU) || (e->flags & EDGE_COMPLEX)
|| prob < branch_th || EDGE_FREQUENCY (e) < exec_th
|| e->count < count_th)
|| ((prob < branch_th || EDGE_FREQUENCY (e) < exec_th
|| e->count < count_th) && (!for_size)))
continue;
/* If partitioning hot/cold basic blocks, don't consider edges
......@@ -558,6 +577,30 @@ find_traces_1_round (int branch_th, int exec_th, gcov_type count_th,
&& copy_bb_p (best_edge->dest, 0))
best_edge = NULL;
/* If the best destination has multiple successors or predecessors,
don't allow it to be added when optimizing for size. This makes
sure predecessors with smaller index are handled before the best
destinarion. It breaks long trace and reduces long jumps.
Take if-then-else as an example.
A
/ \
B C
\ /
D
If we do not remove the best edge B->D/C->D, the final order might
be A B D ... C. C is at the end of the program. If D's successors
and D are complicated, might need long jumps for A->C and C->D.
Similar issue for order: A C D ... B.
After removing the best edge, the final result will be ABCD/ ACBD.
It does not add jump compared with the previous order. But it
reduces the possiblity of long jumps. */
if (best_edge && for_size
&& (EDGE_COUNT (best_edge->dest->succs) > 1
|| EDGE_COUNT (best_edge->dest->preds) > 1))
best_edge = NULL;
/* Add all non-selected successors to the heaps. */
FOR_EACH_EDGE (e, ei, bb->succs)
{
......@@ -599,11 +642,12 @@ find_traces_1_round (int branch_th, int exec_th, gcov_type count_th,
{
/* When partitioning hot/cold basic blocks, make sure
the cold blocks (and only the cold blocks) all get
pushed to the last round of trace collection. */
pushed to the last round of trace collection. When
optimizing for size, do not push to next round. */
if (push_to_next_round_p (e->dest, round,
number_of_rounds,
exec_th, count_th))
if (!for_size && push_to_next_round_p (e->dest, round,
number_of_rounds,
exec_th, count_th))
which_heap = new_heap;
}
......@@ -685,6 +729,8 @@ find_traces_1_round (int branch_th, int exec_th, gcov_type count_th,
(i.e. 2 * B->frequency >= EDGE_FREQUENCY (AC) )
Best ordering is then A B C.
When optimizing for size, A B C is always the best order.
This situation is created for example by:
if (A) B;
......@@ -704,7 +750,8 @@ find_traces_1_round (int branch_th, int exec_th, gcov_type count_th,
& EDGE_CAN_FALLTHRU)
&& !(single_succ_edge (e->dest)->flags & EDGE_COMPLEX)
&& single_succ (e->dest) == best_edge->dest
&& 2 * e->dest->frequency >= EDGE_FREQUENCY (best_edge))
&& (2 * e->dest->frequency >= EDGE_FREQUENCY (best_edge)
|| for_size))
{
best_edge = e;
if (dump_file)
......@@ -824,6 +871,10 @@ bb_to_key (basic_block bb)
edge_iterator ei;
int priority = 0;
/* Use index as key to align with its original order. */
if (optimize_function_for_size_p (cfun))
return bb->index;
/* Do not start in probably never executed blocks. */
if (BB_PARTITION (bb) == BB_COLD_PARTITION
......@@ -869,6 +920,11 @@ better_edge_p (const_basic_block bb, const_edge e, int prob, int freq,
int diff_prob = best_prob / 10;
int diff_freq = best_freq / 10;
/* The smaller one is better to keep the original order. */
if (optimize_function_for_size_p (cfun))
return !cur_best_edge
|| cur_best_edge->dest->index > e->dest->index;
if (prob > best_prob + diff_prob)
/* The edge has higher probability than the temporary best edge. */
is_better_edge = true;
......@@ -904,6 +960,73 @@ better_edge_p (const_basic_block bb, const_edge e, int prob, int freq,
return is_better_edge;
}
/* Return true when the edge E is better than the temporary best edge
CUR_BEST_EDGE. If SRC_INDEX_P is true, the function compares the src bb of
E and CUR_BEST_EDGE; otherwise it will compare the dest bb.
BEST_LEN is the trace length of src (or dest) bb in CUR_BEST_EDGE.
TRACES record the information about traces.
When optimizing for size, the edge with smaller index is better.
When optimizing for speed, the edge with bigger probability or longer trace
is better. */
static bool
connect_better_edge_p (const_edge e, bool src_index_p, int best_len,
const_edge cur_best_edge, struct trace *traces)
{
int e_index;
int b_index;
bool is_better_edge;
if (!cur_best_edge)
return true;
if (optimize_function_for_size_p (cfun))
{
e_index = src_index_p ? e->src->index : e->dest->index;
b_index = src_index_p ? cur_best_edge->src->index
: cur_best_edge->dest->index;
/* The smaller one is better to keep the original order. */
return b_index > e_index;
}
if (src_index_p)
{
e_index = e->src->index;
if (e->probability > cur_best_edge->probability)
/* The edge has higher probability than the temporary best edge. */
is_better_edge = true;
else if (e->probability < cur_best_edge->probability)
/* The edge has lower probability than the temporary best edge. */
is_better_edge = false;
else if (traces[bbd[e_index].end_of_trace].length > best_len)
/* The edge and the temporary best edge have equivalent probabilities.
The edge with longer trace is better. */
is_better_edge = true;
else
is_better_edge = false;
}
else
{
e_index = e->dest->index;
if (e->probability > cur_best_edge->probability)
/* The edge has higher probability than the temporary best edge. */
is_better_edge = true;
else if (e->probability < cur_best_edge->probability)
/* The edge has lower probability than the temporary best edge. */
is_better_edge = false;
else if (traces[bbd[e_index].start_of_trace].length > best_len)
/* The edge and the temporary best edge have equivalent probabilities.
The edge with longer trace is better. */
is_better_edge = true;
else
is_better_edge = false;
}
return is_better_edge;
}
/* Connect traces in array TRACES, N_TRACES is the count of traces. */
static void
......@@ -917,6 +1040,7 @@ connect_traces (int n_traces, struct trace *traces)
int current_partition;
int freq_threshold;
gcov_type count_threshold;
bool for_size = optimize_function_for_size_p (cfun);
freq_threshold = max_entry_frequency * DUPLICATION_THRESHOLD / 1000;
if (max_entry_count < INT_MAX / 1000)
......@@ -980,10 +1104,7 @@ connect_traces (int n_traces, struct trace *traces)
&& bbd[si].end_of_trace >= 0
&& !connected[bbd[si].end_of_trace]
&& (BB_PARTITION (e->src) == current_partition)
&& (!best
|| e->probability > best->probability
|| (e->probability == best->probability
&& traces[bbd[si].end_of_trace].length > best_len)))
&& connect_better_edge_p (e, true, best_len, best, traces))
{
best = e;
best_len = traces[bbd[si].end_of_trace].length;
......@@ -1026,17 +1147,52 @@ connect_traces (int n_traces, struct trace *traces)
&& bbd[di].start_of_trace >= 0
&& !connected[bbd[di].start_of_trace]
&& (BB_PARTITION (e->dest) == current_partition)
&& (!best
|| e->probability > best->probability
|| (e->probability == best->probability
&& traces[bbd[di].start_of_trace].length > best_len)))
&& connect_better_edge_p (e, false, best_len, best, traces))
{
best = e;
best_len = traces[bbd[di].start_of_trace].length;
}
}
if (best)
if (for_size)
{
if (!best)
/* Stop finding the successor traces. */
break;
/* It is OK to connect block n with block n + 1 or a block
before n. For others, only connect to the loop header. */
if (best->dest->index > (traces[t].last->index + 1))
{
int count = EDGE_COUNT (best->dest->preds);
FOR_EACH_EDGE (e, ei, best->dest->preds)
if (e->flags & EDGE_DFS_BACK)
count--;
/* If dest has multiple predecessors, skip it. We expect
that one predecessor with smaller index connects with it
later. */
if (count != 1)
break;
}
/* Only connect Trace n with Trace n + 1. It is conservative
to keep the order as close as possible to the original order.
It also helps to reduce long jumps. */
if (last_trace != bbd[best->dest->index].start_of_trace - 1)
break;
if (dump_file)
fprintf (dump_file, "Connection: %d %d\n",
best->src->index, best->dest->index);
t = bbd[best->dest->index].start_of_trace;
traces[last_trace].last->aux = traces[t].first;
connected[t] = true;
last_trace = t;
}
else if (best)
{
if (dump_file)
{
......@@ -2047,15 +2203,6 @@ gate_handle_reorder_blocks (void)
{
if (targetm.cannot_modify_jumps_p ())
return false;
/* Don't reorder blocks when optimizing for size because extra jump insns may
be created; also barrier may create extra padding.
More correctly we should have a block reordering mode that tried to
minimize the combined size of all the jumps. This would more or less
automatically remove extra jumps, but would also try to use more short
jumps instead of long jumps. */
if (!optimize_function_for_speed_p (cfun))
return false;
return (optimize > 0
&& (flag_reorder_blocks || flag_reorder_blocks_and_partition));
}
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment