Testcase (Compile at -O2 -maltivec -ftree-vectorize):
int a[16*100];
int f(int e)
{
int i;
for(i = 0;i<16*100;i++)
e += a[i];
return e;
}
--------- Cut -----
Currently we get:
ivtmp.42 = (long unsigned int) &a;
vect_var_.36 = { 0, 0, 0, 0 };
<bb 3>:
vect_var_.36 = MEM[index: ivtmp.42] + vect_var_.36;
ivtmp.42 = ivtmp.42 + 16;
if (ivtmp.42 != (long unsigned int) (&a + 6400))
goto <bb 3>;
else
goto <bb 4>;
<bb 4>:
vect_var_.39 = vect_var_.36 v>> 64;
vect_var_.47 = vect_var_.39 + vect_var_.36;
vect_var_.48 = vect_var_.47 v>> 32;
stmp_var_.38 = BIT_FIELD_REF <vect_var_.48 + vect_var_.47, 32, 96>;
return stmp_var_.38 + e;
Though the last add is extra and does not need to be done, we can get rid of it
by having vect_var_.36 being set initially to {e, 0, 0, 0} .
Note this happens with a non zero start also, that is:
int a[16*100];
int f(int e)
{
int i;
e = 1;
for(i = 0;i<16*100;i++)
e += a[i];
return e;
}
--
Summary: Reduction with nonzero start (arbitrary also) causes an
extra add to happen
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: pinskia at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32825
