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On 08/18/11 15:59, Richard Henderson wrote:
> On 08/17/2011 12:21 AM, Richard Guenther wrote:
>> The patch itself looks sensible, though I am surprised ifcvt
>> doesn't run in cfglayout mode (so you have to use reg notes to
>> find probabilities ...)
>
> It does run in cfglayout mode.
>
> Jeff, I believe you're supposed to get the probabilities from some
> combination of
>
> bb->frequency edge->probability EDGE_FREQUENCY(edge)
OK. Here's the revised patch. There's other places in ifcvt.c that
utilize the notes that I didn't modify.
Bootstrapped & regression tested x86_64-unknown-linux-gnu. Also
verified performance data hasn't changed materially.
OK for trunk?
Thanks,
jeff
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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 if profitable.
(find_if_case_2): Similarly for the ELSE clause.
Index: ifcvt.c
===================================================================
*** ifcvt.c (revision 179218)
--- ifcvt.c (working copy)
*************** static int cond_exec_changed_p;
*** 85,91 ****
/* Forward references. */
static int count_bb_insns (const_basic_block);
! static bool cheap_bb_rtx_cost_p (const_basic_block, 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);
--- 85,91 ----
/* Forward references. */
static int count_bb_insns (const_basic_block);
! 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);
*************** count_bb_insns (const_basic_block bb)
*** 131,150 ****
/* 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. */
static bool
! cheap_bb_rtx_cost_p (const_basic_block bb, int max_cost)
{
int count = 0;
rtx insn = BB_HEAD (bb);
bool speed = optimize_bb_for_speed_p (bb);
while (1)
{
if (NONJUMP_INSN_P (insn))
{
! int cost = insn_rtx_cost (PATTERN (insn), speed);
if (cost == 0)
return false;
--- 131,161 ----
/* 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.
!
! 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 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) * REG_BR_PROB_BASE;
if (cost == 0)
return false;
*************** find_if_case_1 (basic_block test_bb, edg
*** 3796,3803 ****
basic_block then_bb = then_edge->dest;
basic_block else_bb = else_edge->dest;
basic_block new_bb;
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
--- 3807,3814 ----
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;
/* If we are partitioning hot/cold basic blocks, we don't want to
mess up unconditional or indirect jumps that cross between hot
*************** find_if_case_1 (basic_block test_bb, edg
*** 3840,3847 ****
"\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,
COSTS_N_INSNS (BRANCH_COST (optimize_bb_for_speed_p (then_edge->src),
predictable_edge_p (then_edge)))))
return FALSE;
--- 3851,3864 ----
"\nIF-CASE-1 found, start %d, then %d\n",
test_bb->index, then_bb->index);
! 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;
*************** find_if_case_2 (basic_block test_bb, edg
*** 3910,3916 ****
basic_block then_bb = then_edge->dest;
basic_block else_bb = else_edge->dest;
edge else_succ;
! rtx note;
/* If we are partitioning hot/cold basic blocks, we don't want to
mess up unconditional or indirect jumps that cross between hot
--- 3927,3933 ----
basic_block then_bb = then_edge->dest;
basic_block else_bb = else_edge->dest;
edge else_succ;
! 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
*************** find_if_case_2 (basic_block test_bb, edg
*** 3949,3957 ****
if (then_bb->index < NUM_FIXED_BLOCKS)
return FALSE;
/* 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)
;
else if (else_succ->dest->index < NUM_FIXED_BLOCKS
|| dominated_by_p (CDI_POST_DOMINATORS, then_bb,
--- 3966,3984 ----
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. */
! if (else_prob > then_prob)
;
else if (else_succ->dest->index < NUM_FIXED_BLOCKS
|| dominated_by_p (CDI_POST_DOMINATORS, then_bb,
*************** find_if_case_2 (basic_block test_bb, edg
*** 3966,3973 ****
"\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,
COSTS_N_INSNS (BRANCH_COST (optimize_bb_for_speed_p (else_edge->src),
predictable_edge_p (else_edge)))))
return FALSE;
--- 3993,4001 ----
"\nIF-CASE-2 found, start %d, else %d\n",
test_bb->index, else_bb->index);
! /* 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;
