------- Comment #4 from amacleod at redhat dot com 2006-10-02 13:56 -------
This is not something out of ssa can resolve on its own.
given this sequence:
# s_2 = PHI <s_5(0), s_9(1)>;
# d_1 = PHI <d_6(0), d_10(1)>;
<L0>:;
D.1287_8 = MEM[base: d_1];
s_9 = s_2 + D.1287_8; <<<--- s_2 and s_9 have different values
d_10 = d_1 + 4B;
if (s_9 < g_11) goto <L0>; else goto <L1>;
# s_7 = PHI <s_2(1)>; <<<--- original value of s_2 used here
<L1>:;
*v_3 = s_7;
When s_9 is assigned s_2 + D.1287_8 , they have different values, so when s_2
is used in the PHI assigned to s_7, there is a stretch over which s_9 and s_2
are both live, and contain different values.
out of ssa cannot assign them to the same variable.
you are going to have a copy in the loop no matter what you do...
right now we get:
<bb 2>:
s = *(v + 4B);
<L0>:;
s.31 = s + MEM[base: d]{*d};
d = d + 4B;
if (s.31 < g) goto <L6>; else goto <L1>;
<L6>:;
s = s.31;
goto <bb 3> (<L0>);
<L1>:;
*v = s;
return;
the other alternative would be:
<L0>:;
s.31 = s
s = s + MEM[base: d]{*d};
d = d + 4B;
if (s < g) goto <L6>; else goto <L1>;
<L6>:;
goto <bb 3> (<L0>);
<L1>:;
*v = s.31;
Is that any better? It looks pretty much the same to me. It might help on a 2
address machine where you need r1 = r1 + exp, but that about it.
so Im not sure I understand what you want out of ssa to do with the code here.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27986
