Strengthen out-of-bounds guarantees for buffer accesses by disallowing
buffer accesses with alignment lower than natural alignment.
This is needed to specifically address the edge case where an access
starts out-of-bounds and then enters in-bounds, as the hardware would
treat the entire access as being out-of-bounds. This is normally not
needed for most users, but at least one graphics device extension
(VK_EXT_robustness2) has very strict requirements - in-bounds accesses
must return correct value, and out-of-bounds accesses must return zero.
The direct consequence of the patch is that a buffer access at negative
address is not merged by load-store-vectorizer with one at a positive
address, which fixes a CTS test.
Targets that do not care about the new behavior are advised to use the
new target feature relaxed-buffer-oob-mode that maintains the state from
before the patch.
170c0dac44