On 12/20/21 12:29 PM, Jeff Law wrote:
On 12/16/2021 12:56 PM, Martin Sebor via Gcc-patches wrote:
Enabling vectorization at -O2 caused quite a few tests for
warnings to start failing in GCC 12. These tests were xfailed
and bugs were opened to track the problems until they can be
fully analyzed and ultimately fixed before GCC 12 is released.
I've now started going through these and the first such bug
I tackled is PR 102944. As it turns out, the xfails there
are all due to a known limitation tracked in PR 101475: when
determining the size of a destination for A COMPONENT_REF,
unless asked for the size of the complete object,
compute_objsize() only considers the size of the referenced
member, even when the member is larger than the object would
allow. This prevents warnings from diagnosing unvectorized
past-the-end accesses to objects in backing buffers (such as
in character arrays or allocated chunks of memory).
Many (though not all) accesses that are vectorized are diagnosed
because there the COMPONENT_REF is replaced by a MEM_REF. But
because vectorization depends on target-specific things like
alignment requirements, what is and isn't diagnosed also tends
to be target-specific, making these tests quite brittle..
The attached patch corrects this oversight by using the complete
object's size instead of the member when the former is smaller.
Besides improving the out-of-bounds access detection it also
makes the tests behave more consistently across targets.
Tested on x86_64-linux and by building Glibc and verifying
that the change triggers no new warnings.
I must be missing something here. How can the enclosing object be
smaller than a member?
When the enclosing object is backed by a buffer of insufficient
size. The buffer might be a declared character array such as
in the the tests added and modified by the patch, or it might
be dynamically allocated.
Martin
