------- Additional Comments From steven at gcc dot gnu dot org 2004-12-24
12:52 -------
Silly bugzilla... Sorry about that.
A piece of unidiff, then. (-) is the smaller test that works, (+) is the
test where we get the extra copy. What I wanted to show is that only the
root variable is different in the PHI argument:
@@ -28,10 +29,10 @@
# BLOCK 1
# PRED: 0 [100.0%] (fallthru,exec) 1 [89.0%] (dfs_back,false,exec)
- # temp2D.1464_1 = PHI <temp2D.1464_2(0), temp2D.1464_4(1)>;
+ # temp2D.1464_1 = PHI <temp2D.1464_2(0), temp1D.1468_4(1)>;
<L0>:;
- temp2D.1464_4 = temp2D.1464_1 * xlvj_D.1465_3;
- if (temp2D.1464_4 != 0) goto <L2>; else goto <L0>;
+ temp1D.1468_4 = temp2D.1464_1 * xlvj_D.1465_3;
+ if (temp1D.1468_4 != 0) goto <L2>; else goto <L0>;
# SUCC: 2 [11.0%] (loop_exit,true,exec) 1 [89.0%] (dfs_back,false,exec)
# BLOCK 2
@@ -48,45 +49,45 @@
This comes from DOM copy-proping around the loop. Before DOM1 we have
a function that looks like this (.dce1):
;; Function f (f)
f (temp2, xlvj_)
{
int temp1;
int D.1471;
# temp2_1 = PHI <temp2_2(-1), temp2_5(0)>;
<L0>:;
temp1_4 = temp2_1 * xlvj__3;
temp2_5 = temp1_4;
if (temp1_4 != 0) goto <L2>; else goto <L0>;
<L2>:;
xlvj__6 = xlvj__3;
return xlvj__6;
}
After DOM1 (the .dom1 dump) we have this:
;; Function f (f)
f (temp2, xlvj_)
{
int temp1;
int D.1471;
# temp2_1 = PHI <temp2_2(-1), temp1_4(0)>;
<L0>:;
temp1_4 = temp2_1 * xlvj__3;
temp2_5 = temp1_4;
if (temp1_4 != 0) goto <L2>; else goto <L0>;
<L2>:;
xlvj__6 = xlvj__3;
return xlvj__3;
}
We never recover from this, we don't coalesce, and there's your copy.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19038
