------- Comment #3 from jakub at gcc dot gnu dot org 2008-08-14 10:02 -------
Somewhat shorter:
extern void abort (void);
unsigned int a, b = 1, c;
void __attribute__ ((noinline))
foo (int x)
{
if (x != 5)
abort ();
}
int
main ()
{
unsigned int d, e;
for (d = 1; d < 5; d++)
if (c)
a = b;
a = b;
e = a << 1;
if (e)
e = (e << 1) ^ 1;
foo (e);
return 0;
}
At *.tailc looks sane to me.
<bb 2>:
pretmp.35_15 = c;
b.1_5 = b;
a_lsm.48_4 = a;
if (pretmp.35_15 != 0)
goto <bb 3>;
else
goto <bb 4>;
<bb 3>:
<bb 4>:
# a_lsm.48_28 = PHI <b.1_5(3), a_lsm.48_4(2)>
a = b.1_5;
e_9 = b.1_5 << 1;
if (e_9 != 0)
goto <bb 5>;
else
goto <bb 6>;
so a_lsm.48_28 is either b or a, depending on whether c != 0 or not, and a = b.
Then copyrename4 decides to replace a = b.1_5; with a = a_lsm_48_5; and at
*.uncprop we have:
<bb 2>:
pretmp.35_15 = c;
a_lsm.48_5 = b;
a_lsm.48_4 = a;
if (pretmp.35_15 != 0)
goto <bb 3>;
else
goto <bb 4>;
<bb 3>:
<bb 4>:
# a_lsm.48_28 = PHI <a_lsm.48_5(3), a_lsm.48_4(2)>
a = a_lsm.48_5;
e_9 = a_lsm.48_5 << 1;
if (e_9 != 0)
goto <bb 5>;
else
goto <bb 6>;
which looks correct too. But *.optimized is already wrong:
<bb 2>:
a_lsm.49 = b;
a_lsm.48 = a;
if (c != 0)
goto <bb 3>;
else
goto <bb 7>;
<bb 7>:
a_lsm.49 = a_lsm.48;
goto <bb 4>;
<bb 3>:
<bb 4>:
a = a_lsm.49;
e = a_lsm.49 << 1;
if (e != 0)
goto <bb 5>;
else
goto <bb 8>;
While in *.uncprop a was set unconditionally to b, now it is sometimes b and
sometimes a.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37102
