On Jan 4, 2017, Alexandre Oliva <aol...@redhat.com> wrote:
> I'll prepare and post a patch anyway, but do we want to make it
> standard practice?
Here it is.
simplify_transformation_to_array had the nested loop unrolled 7 times,
which is reasonable given that it iterates over arrays of size
GFC_MAX_DIMENSIONS == 7.
The problem is that the last iteration increments the index, tests
that it's less than result->rank, and then accesses the arrays with
the incremented index.
We did not optimize out that part in the 7th iteration, so VRP flagged
the unreachable code as accessing arrays past the end.
It couldn't possibly know that we'd never reach that part, since the
test was on result->rank, and it's not obvious (for the compiler) that
result->rank <= GFC_MAX_DIMENSIONS.
Even an assert to that effect before the enclosing loop didn't avoid
the warning turned to error, though; I suppose there might be some
aliasing at play, because moving the assert into the loop does. An
assert on the index itself would also work, even more efficiently, but
we're just silencing the warning instead.
Regstrapped on x86_64-linux-gnu and i686-linux-gnu. Ok to install?
for gcc/fortran/ChangeLog
* simplify.c (simplify_transformation_to_array): Silence
array bounds warning. Fix whitespace.
---
gcc/fortran/simplify.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/gcc/fortran/simplify.c b/gcc/fortran/simplify.c
index 549d9005..db860f7 100644
--- a/gcc/fortran/simplify.c
+++ b/gcc/fortran/simplify.c
@@ -610,9 +610,18 @@ simplify_transformation_to_array (gfc_expr *result,
gfc_expr *array, gfc_expr *d
n++;
if (n < result->rank)
{
- count [n]++;
+#pragma GCC diagnostic push
+ /* If the nested loop is unrolled GFC_MAX_DIMENSIONS
+ times, we'd warn for the last iteration, because the
+ array index will have already been incremented to the
+ array sizes, and we can't tell that this must make
+ the test against result->rank false, because ranks
+ must not exceed GFC_MAX_DIMENSIONS. */
+#pragma GCC diagnostic ignored "-Warray-bounds"
+ count[n]++;
base += sstride[n];
dest += dstride[n];
+#pragma GCC diagnostic pop
}
else
done = true;
--
Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/ FSF Latin America board member
Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer
