This testcase:
int test (double a) {
return __builtin_signbit (a + 1.0);
}
produces quite non-optimal code when compiled with '-O2' (-fomit-frame-pointer):
test:
subl $12, %esp
! xorl %eax, %eax
! movl $1072693248, %edx
! movl %eax, (%esp)
! movl %edx, 4(%esp)
! fldl (%esp)
faddl 16(%esp)
fstpl (%esp)
? movl 4(%esp), %edx
addl $12, %esp
? movl %edx, %eax
andl $-2147483648, %eax
ret
Instructions marked with (!) could be replaced with a fld1.
Instructions marked with (?) could be replaced with a "movl 4(%esp), %eax".
Perhaps fxam could be used in this case? Then the code would look something
like:
fldl 4(%esp)
fxam
fnstsw %ax
fstp %st(0)
andl 0x02, %eax
ret
--
Summary: non-optimal code with __builtin_signbit
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: uros at kss-loka dot si
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21508
