http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58895
Bug ID: 58895
Summary: [SH] improve handling of signbit result
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: olegendo at gcc dot gnu.org
Target: sh*-*-*
The handling of the result of the floating point signbit functions could be
improved in the following cases.
#include <cmath>
bool test0_OK (float x)
{
return !std::signbit (x);
}
-m4-single -m4 -O2:
flds fr4,fpul
sts fpul,r1
cmp/pz r1
rts
movt r0
----------------------
bool test1_NG (float x)
{
return std::signbit (x);
}
-m4-single -m4 -O2:
flds fr4,fpul
sts fpul,r1
cmp/pz r1
movt r0
rts
xor #1,r0
better:
flds fr4,fpul
sts fpul,r1
shll r1
rts
movt r1,r0
----------------------
void test2_OK (float x, int* y)
{
y[0] = !std::signbit (x);
}
-m4-single -m4 -O2:
flds fr4,fpul
sts fpul,r1
cmp/pz r1
movt r1
rts
mov.l r1,@r4
----------------------
void test3_NG (float x, int* y)
{
// c++11 std::signbit returns a bool
y[0] = std::signbit (x);
}
-m4-single -m4 -O2:
flds fr4,fpul
sts fpul,r1
cmp/pz r1
mov #-1,r1
negc r1,r1
rts
mov.l r1,@r4
better:
flds fr4,fpul
sts fpul,r2
shll r2
movt r1
rts
mov.l r1,@r4
----------------------
void test4_NG (float x, int* y)
{
// c99 signbit macro and corresponding built-in return
// zero or non-zero integer, i.e. MSB of x.
y[0] = __builtin_signbitf (x);
}
-m4-single -m4 -O2:
flds fr4,fpul
sts fpul,r2
mov.l .L7,r1
and r2,r1
rts
mov.l r1,@r4
.L8:
.align 2
.L7:
.long -2147483648
possible alternative without 32 bit constant.
smaller size, but probably slower.
flds fr4,fpul
sts fpul,r2
shll r2
movt r1
rotcr r1
rts
mov.l r1,@r4
