------- Comment #2 from jakub at gcc dot gnu dot org 2007-11-22 15:19 -------
On the simplified:
extern int s;
void
foo (int *x, int y, int z)
{
int m, n;
int o;
int p = x[0];
o = s;
for (m = 0; m < s; m++)
for (n = 0; n < s; n++)
{
if (x[n] != p)
continue;
if (m > z)
z = m;
if (n < o)
o = n;
}
for (m = y; m <= z; m++)
{
}
}
at -O2 -ftree-loop-linear, it fails everywhere I tried, on x86_64-linux with
both -m{32,64}, on i686-linux, on sparc64-linux with -m{32,64} and on
ppc64-linux
with -m{32,64}.
<bb 5>:
# o_42 = PHI <o_8(4), o_1(12)>
# n_40 = PHI <n_25(4), 0(12)>
# z_35 = PHI <z_2(4), z_34(12)>
D.1559_19 = (long unsigned int) n_40;
D.1560_20 = D.1559_19 * 4;
D.1561_21 = x_11(D) + D.1560_20;
D.1562_22 = *D.1561_21;
if (D.1562_22 != p_12)
goto <bb 8>;
else
goto <bb 6>;
<bb 6>:
z_17 = MAX_EXPR <z_35, m_38>;
if (n_40 < o_42)
goto <bb 8>;
else
goto <bb 7>;
<bb 7>:
<bb 8>:
# o_8 = PHI <o_42(5), o_42(7), n_40(6)>
# z_2 = PHI <z_35(5), z_17(7), z_17(6)>
n_25 = n_40 + 1;
if (o_13 > n_25)
goto <bb 4>;
else
goto <bb 9>;
This is with IV n_40, oldiv_stmt is # n_40 = PHI <n_25(4), 0(12)> and one
of the immediate uses is # o_8 = PHI <o_42(5), o_42(7), n_40(6)>
That could have been perhaps transformed into a MIN_EXPR, but unlike the
MAX_EXPR phiopt1 has not done that, because there weren't just 2 incoming
edges, but 3 (where two used one value and the third different one).
I don't see justification for the assert that none of the immediate uses of
the IV is a PHI_NODE - it can certainly happen and while it can be harder to
fix up, perhaps involving adding some statements on edges, it is nothing
that should prevent the transformations.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34017
