Doug Gregor f36d2d3978 [Source manager] Improve the performance of findBufferContainingLocInternal() ...

This function was performing a linear scan through the set of known
buffers to find the buffer containing a given source location. This
linear scan can show up in hot loops, and the number of buffers in a
program is increasing due to macros, so this has become a performance
problem.

Replace the linear scan with a logarithmic lookup into a sorted vector
of the buffer IDs, with a one-element most-recently-used cache so that
repeated lookups in the same buffer require constant time.

This mirrors what we already do with source files in a module.
Unfortunately, we cannot reuse that code because there is no link from
buffers to source files. We should look to consolidate this in the
future.

Fixes rdar://116184248.

2023-10-04 14:37:34 -07:00

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