[NFC][Attributor] Reach fixpoint in call site AACallEdges for direct calls (#237632)
A direct call whose callee has no callback metadata only calls its
callee, so its call site `AACallEdges` cannot change after
initialization. Add the edge in initialize and reach a fixpoint there,
instead of updating the attribute twice to find out.
`AACallEdgesFunction` already skips the call site attribute for such
calls since #232616; both now share `getOnlyCallee()`.
Other attributes still create call site AACallEdges for direct calls,
e.g., `AAInterFnReachability` and the AMDGPU attributor. On a generated
module with 2,001 functions and 15,986 calls, this removes all updates
of call site `AACallEdges`. The total number of updates goes from
304,263 to 272,291 with `-passes=attributor`, from 207,815 to 175,843
with `-passes=attributor-light`, and from 35,977 to 16,005 with
`-passes=amdgpu-attributor`. The wall time does not change measurably on
that module, because these updates are cheap.
This PR was assisted by AI but I reviewed all the changes.
llvm-project
322af988 - [NFC][Attributor] Reach fixpoint in call site AACallEdges for direct calls (#237632)
