llvm: Fix alloca alignment and type selection in AllocOpt (#60699)
Inherit alignment from the original GC allocation with
JL_SMALL_BYTE_ALIGNMENT
as the minimum. Use alignment-sized integer chunks for the alloca type
(matching emit_static_alloca) so SROA splits allocations into aligned
pieces
for better performance and vectorization.
Also adds the missing setAlignment call in splitOnStack.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
(cherry picked from commit 54fde7e012e6883a5bc9acd964593c8b9c9b5c74)