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ifcvt.c (cheap_bb_rtx_cost_p): Add SCALE argument.

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* ifcvt.c (cheap_bb_rtx_cost_p): Add SCALE argument.  Scale
	non-jumping insns by REG_BR_PROB_BASE and the maximum cost
	by SCALE.
	(find_if_case_1): Use the probability of the THEN clause when
	determining if speculation is profitable.
	(find_if_case_2): Similarly for the ELSE clause.

From-SVN: r179284
This commit is contained in:
Jeff Law 2011-09-27 10:49:17 -06:00 committed by Jeff Law
parent 9b7ab6d6e0
commit 16a275d29d
2 changed files with 49 additions and 12 deletions
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9
gcc/ChangeLog
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@ -1,3 +1,12 @@
2011-09-27 Jeff Law <law@redhat.com>
* ifcvt.c (cheap_bb_rtx_cost_p): Add SCALE argument. Scale
non-jumping insns by REG_BR_PROB_BASE and the maximum cost
by SCALE.
(find_if_case_1): Use the probability of the THEN clause when
determining if speculation is profitable.
(find_if_case_2): Similarly for the ELSE clause.
2011-09-27 Jakub Jelinek <jakub@redhat.com>
* common.opt: Add -foptimize-strlen option.

52
gcc/ifcvt.c
View File

@ -85,7 +85,7 @@ static int cond_exec_changed_p;
/* Forward references. */
static int count_bb_insns (const_basic_block);
static bool cheap_bb_rtx_cost_p (const_basic_block, int);
static bool cheap_bb_rtx_cost_p (const_basic_block, int, int);
static rtx first_active_insn (basic_block);
static rtx last_active_insn (basic_block, int);
static rtx find_active_insn_before (basic_block, rtx);
@ -131,20 +131,31 @@ count_bb_insns (const_basic_block bb)
/* Determine whether the total insn_rtx_cost on non-jump insns in
basic block BB is less than MAX_COST. This function returns
false if the cost of any instruction could not be estimated. */
false if the cost of any instruction could not be estimated.
The cost of the non-jump insns in BB is scaled by REG_BR_PROB_BASE
as those insns are being speculated. MAX_COST is scaled with SCALE
plus a small fudge factor. */
static bool
cheap_bb_rtx_cost_p (const_basic_block bb, int max_cost)
cheap_bb_rtx_cost_p (const_basic_block bb, int scale, int max_cost)
{
int count = 0;
rtx insn = BB_HEAD (bb);
bool speed = optimize_bb_for_speed_p (bb);
/* Our branch probability/scaling factors are just estimates and don't
account for cases where we can get speculation for free and other
secondary benefits. So we fudge the scale factor to make speculating
appear a little more profitable. */
scale += REG_BR_PROB_BASE / 8;
max_cost *= scale;
while (1)
{
if (NONJUMP_INSN_P (insn))
{
int cost = insn_rtx_cost (PATTERN (insn), speed);
int cost = insn_rtx_cost (PATTERN (insn), speed) * REG_BR_PROB_BASE;
if (cost == 0)
return false;
@ -3796,8 +3807,8 @@ find_if_case_1 (basic_block test_bb, edge then_edge, edge else_edge)
basic_block then_bb = then_edge->dest;
basic_block else_bb = else_edge->dest;
basic_block new_bb;
int then_bb_index, then_prob;
rtx else_target = NULL_RTX;
int then_bb_index;
/* If we are partitioning hot/cold basic blocks, we don't want to
mess up unconditional or indirect jumps that cross between hot
@ -3840,8 +3851,14 @@ find_if_case_1 (basic_block test_bb, edge then_edge, edge else_edge)
"\nIF-CASE-1 found, start %d, then %d\n",
test_bb->index, then_bb->index);
/* THEN is small. */
if (! cheap_bb_rtx_cost_p (then_bb,
if (then_edge->probability)
then_prob = REG_BR_PROB_BASE - then_edge->probability;
else
then_prob = REG_BR_PROB_BASE / 2;
/* We're speculating from the THEN path, we want to make sure the cost
of speculation is within reason. */
if (! cheap_bb_rtx_cost_p (then_bb, then_prob,
COSTS_N_INSNS (BRANCH_COST (optimize_bb_for_speed_p (then_edge->src),
predictable_edge_p (then_edge)))))
return FALSE;
@ -3910,7 +3927,7 @@ find_if_case_2 (basic_block test_bb, edge then_edge, edge else_edge)
basic_block then_bb = then_edge->dest;
basic_block else_bb = else_edge->dest;
edge else_succ;
rtx note;
int then_prob, else_prob;
/* If we are partitioning hot/cold basic blocks, we don't want to
mess up unconditional or indirect jumps that cross between hot
@ -3949,9 +3966,19 @@ find_if_case_2 (basic_block test_bb, edge then_edge, edge else_edge)
if (then_bb->index < NUM_FIXED_BLOCKS)
return FALSE;
if (else_edge->probability)
{
else_prob = else_edge->probability;
then_prob = REG_BR_PROB_BASE - else_prob;
}
else
{
else_prob = REG_BR_PROB_BASE / 2;
then_prob = REG_BR_PROB_BASE / 2;
}
/* ELSE is predicted or SUCC(ELSE) postdominates THEN. */
note = find_reg_note (BB_END (test_bb), REG_BR_PROB, NULL_RTX);
if (note && INTVAL (XEXP (note, 0)) >= REG_BR_PROB_BASE / 2)
if (else_prob > then_prob)
;
else if (else_succ->dest->index < NUM_FIXED_BLOCKS
|| dominated_by_p (CDI_POST_DOMINATORS, then_bb,
@ -3966,8 +3993,9 @@ find_if_case_2 (basic_block test_bb, edge then_edge, edge else_edge)
"\nIF-CASE-2 found, start %d, else %d\n",
test_bb->index, else_bb->index);
/* ELSE is small. */
if (! cheap_bb_rtx_cost_p (else_bb,
/* We're speculating from the ELSE path, we want to make sure the cost
of speculation is within reason. */
if (! cheap_bb_rtx_cost_p (else_bb, else_prob,
COSTS_N_INSNS (BRANCH_COST (optimize_bb_for_speed_p (else_edge->src),
predictable_edge_p (else_edge)))))
return FALSE;