We can derive and upgrade alignment for loads/stores using other
well-aligned loads/stores. This optimization does a single forward pass through
each basic block and uses loads/stores (the alignment and the offset) to
derive the best possible alignment for a base pointer, caching the
result. If it encounters another load/store based on that pointer, it
tries to upgrade the alignment. The optimization must be a forward pass within a basic
block because control flow and exception throwing can impact alignment guarantees.
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Co-authored-by: Nikita Popov <github@npopov.com>
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