[SPIR-V] Fix some GEP legalization (#150943)

Pointers and GEP are untyped. SPIR-V required structured OpAccessChain.
This means the backend will have to determine a good way to retrieve the
structured access from an untyped GEP. This is not a trivial problem,
and needs to be addressed to have a robust compiler.

The issue is other workstreams relies on the access chain deduction to
work. So we have 2 options:
 - pause all dependent work until we have a good chain deduction.
- submit this limited fix to we can work on both this and other features
in parallel.

Choice we want to make is #2: submitting this **knowing this is not a
good** fix. It only increase the number of patterns we can work with,
thus allowing others to continue working on other parts of the backend.

This patch as-is has many limitations:
- If cannot robustly determine the depth of the structured access from a
GEP. Fixing this would require looking ahead at the full GEP chain.
- It cannot always figure out the correct access indices, especially
with dynamic indices. This will require frontend collaboration.

Because we know this is a temporary hack, this patch only impacts the
logical SPIR-V target. Physical SPIR-V, which can rely on pointer cast
remains on the old method.

Related to #145002

0 files changed, 0 insertions, 0 deletions