------- Comment #4 from zsojka at seznam dot cz 2010-09-07 21:50 -------
However, this optimization in RTL doesn't happen in all cases. For x86_64-linux
(with or without -m32):
----- testcase.c -----
_Bool foo(unsigned i)
{
return (i >> 5) > 10;
}
_Bool bar(unsigned i)
{
return i > (10 << 5);
}
int fooi(unsigned i)
{
return (i >> 5) > 10;
}
int bari(unsigned i)
{
return i > (10 << 5);
}
----------------------
Compiled with:
$ gcc-4.6.0-pre9999 tst6.c -O3 -S -m32 -fomit-frame-pointer
(svn r162190)
Results in:
foo:
movl 4(%esp), %eax
shrl $5, %eax
cmpl $10, %eax
seta %al
ret
bar:
cmpl $320, 4(%esp)
seta %al
ret
fooi:
movl 4(%esp), %eax
shrl $5, %eax
cmpl $10, %eax
seta %al
movzbl %al, %eax
ret
bari:
xorl %eax, %eax
cmpl $320, 4(%esp)
seta %al
ret
When compiled with -m64 it gets a bit better because parameter is in edi
instead of in stack, but the problem is still there. Should I open separate PR
for this?
--
zsojka at seznam dot cz changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |zsojka at seznam dot cz
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20517
