[Bug tree-optimization/37699] New: [alias-improvements-branch] can't alias ptr and local array

["dorit at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

This happens in gcc.dg/vect/vect-96.c and gcc.dg/vect/no-vfa-vect-43.c.

In the first, we can't distinguish between a write through a (local) pointer to
a global array (which is a field in a struct), and a read from a local array. s
a result we vectorize the loop using loop-versioning controled by a run-time
aliasing test, which also means we'll use versioning instead of peeling to
align a misaligned store.

In the second, we can't tell that reads through a pointer (which is a function
argument) do not overlap with a write to a local array. As a result we try to
vectorize the loop using loop-versioning controled by a run-time aliasing
test, however this testcase doe not allow that (--param
vect-max-version-for-alias-checks=0), so vectorization fails.


-- 
           Summary: [alias-improvements-branch] can't alias ptr and local
                    array
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dorit at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37699