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ifcvt: improve cost estimation (PR 87047)

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PR rtl-optimization/87047
	* ifcvt.c (average_cost): New static function.  Use it...
	(noce_process_if_block): ... here.

testsuite/
	* gcc.dg/pr87047.c: New test.

From-SVN: r276466
This commit is contained in:
Alexander Monakov 2019-10-02 18:37:12 +03:00 committed by Alexander Monakov
parent a264ea9a5b
commit 1764d63bd9
5 changed files with 45 additions and 6 deletions
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6
gcc/ChangeLog
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@ -1,3 +1,9 @@
2019-10-02 Alexander Monakov <amonakov@ispras.ru>
PR rtl-optimization/87047
* ifcvt.c (average_cost): New static function. Use it...
(noce_process_if_block): ... here.
2019-10-02 Aaron Sawdey <acsawdey@linux.ibm.com>
* config/rs6000/rs6000-protos.h (expand_block_move): Change prototype.

17
gcc/ifcvt.c
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@ -3358,6 +3358,16 @@ bb_ok_for_noce_convert_multiple_sets (basic_block test_bb)
return count > 1 && count <= param;
}
/* Compute average of two given costs weighted by relative probabilities
of respective basic blocks in an IF-THEN-ELSE. E is the IF-THEN edge.
With P as the probability to take the IF-THEN branch, return
P * THEN_COST + (1 - P) * ELSE_COST. */
static unsigned
average_cost (unsigned then_cost, unsigned else_cost, edge e)
{
return else_cost + e->probability.apply ((signed) (then_cost - else_cost));
}
/* Given a simple IF-THEN-JOIN or IF-THEN-ELSE-JOIN block, attempt to convert
it without using conditional execution. Return TRUE if we were successful
at converting the block. */
@ -3413,10 +3423,9 @@ noce_process_if_block (struct noce_if_info *if_info)
&if_info->else_simple))
return false;
if (else_bb == NULL)
if_info->original_cost += then_cost;
else if (speed_p)
if_info->original_cost += MIN (then_cost, else_cost);
if (speed_p)
if_info->original_cost += average_cost (then_cost, else_cost,
find_edge (test_bb, then_bb));
else
if_info->original_cost += then_cost + else_cost;

4
gcc/ifcvt.h
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@ -97,8 +97,8 @@ struct noce_if_info
/* An estimate of the original costs. When optimizing for size, this is the
combined cost of COND, JUMP and the costs for THEN_BB and ELSE_BB.
When optimizing for speed, we use the costs of COND plus the minimum of
the costs for THEN_BB and ELSE_BB, as computed in the next field. */
When optimizing for speed, we use the costs of COND plus weighted average
of the costs for THEN_BB and ELSE_BB, as computed in the next field. */
unsigned int original_cost;
/* Maximum permissible cost for the unconditional sequence we should

5
gcc/testsuite/ChangeLog
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@ -1,3 +1,8 @@
2019-10-02 Alexander Monakov <amonakov@ispras.ru>
PR rtl-optimization/87047
* gcc.dg/pr87047.c: New test.
2019-10-02 Martin Jambor <mjambor@suse.cz>
PR testsuite/91842

19
gcc/testsuite/gcc.dg/pr87047.c Normal file
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@ -0,0 +1,19 @@
/* { dg-do compile { target { { i?86-*-* x86_64-*-* } && { ! ia32 } } } } */
/* { dg-options "-fdump-rtl-ce1 -O2" } */
typedef unsigned long long uint64_t;
static uint64_t umulh(uint64_t a, uint64_t b)
{
return (unsigned __int128)a*b >> 64;
}
uint64_t f(uint64_t a, uint64_t b, int c)
{
if (c)
a = umulh(a, (b-umulh(a,b))<<44) << 1;
return a;
}
/* { dg-final { scan-rtl-dump "0 true changes made" "ce1" } } */
/* { dg-final { scan-assembler-not "cmov" } } */