https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66997
Bug ID: 66997
Summary: outer loop reduction fails to parallelize with
graphite
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: vries at gcc dot gnu.org
Target Milestone: ---
When running autopar.exp with
--target_board=unix/-ffast-math/-floop-parallelize-all, we run into:
...
FAIL: gcc.dg/autopar/uns-outer-6.c scan-tree-dump-times optimized "loopfn" 4
FAIL: gcc.dg/autopar/uns-outer-6.c scan-tree-dump-times parloops "parallelizing
outer loop" 1
...
[ We can drop -ffast-math once
https://gcc.gnu.org/ml/gcc-patches/2015-07/msg01863.html has been committed. ]
relevant function in uns-outer-6.c:
...
void __attribute__((noinline))
parloop (int N)
{
int i, j;
unsigned int sum;
/* Outer loop reduction, outerloop is parallelized. */
sum=0;
for (i = 0; i < N; i++)
{
for (j = 0; j < N; j++)
y[i]=x[i][j];
sum += y[i];
}
g_sum = sum;
}
...
we find in the parloops dump:
...
Trying loop 3 as candidate
loop 3 is not innermost
loop is not parallel according to graphite
...
