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* [Bug tree-optimization/65442] New: pass_lim misses support for exit-first loops
@ 2015-03-16 14:58 vries at gcc dot gnu.org
2015-03-18 11:36 ` [Bug tree-optimization/65442] " rguenth at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: vries at gcc dot gnu.org @ 2015-03-16 14:58 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65442
Bug ID: 65442
Summary: pass_lim misses support for exit-first loops
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: vries at gcc dot gnu.org
Consider test.c:
...
#include <string.h>
const char *something (void);
size_t
f (unsigned int n)
{
const char *s = something ();
size_t sum = 0;
size_t t;
unsigned int i;
if (!s)
return 0;
for (i = 0; i < n; ++i)
{
t = strlen (s);
sum += t;
}
return sum;
}
...
The resulting code with -O2 -fno-tree-ch from the optimized dump is:
...
f (unsigned int n)
{
unsigned int i;
size_t t;
size_t sum;
const char * s;
size_t _3;
<bb 2>:
s_6 = something ();
if (s_6 == 0B)
goto <bb 6>;
else
goto <bb 3>;
<bb 3>:
# sum_14 = PHI <0(2)>
# i_12 = PHI <0(2)>
goto <bb 5>;
<bb 4>:
t_9 = strlen (s_6);
sum_10 = sum_1 + t_9;
i_11 = i_2 + 1;
<bb 5>:
# sum_1 = PHI <sum_14(3), sum_10(4)>
# i_2 = PHI <i_12(3), i_11(4)>
if (i_2 != n_8(D))
goto <bb 4>;
else
goto <bb 6>;
<bb 6>:
# _3 = PHI <0(2), sum_1(5)>
return _3;
}
...
The strlen is not taken out of the loop. It could be taken out of the loop,
provided it's guarded with the loop condition.
This PR is similar to PR65440. There the strlen is conditional in the loop
body, which is entered unconditionally. Here the strlen is unconditional in the
loop body, which is entered conditionally.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2015-03-16 14:58 [Bug tree-optimization/65442] New: pass_lim misses support for exit-first loops vries at gcc dot gnu.org
2015-03-18 11:36 ` [Bug tree-optimization/65442] " rguenth at gcc dot gnu.org
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