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
