## Purpose

This patch is one in a series of code-mods that annotate LLVM’s public
interface for export. This patch annotates the remaining LLVM CodeGen
and CodeGenTypes library interfaces that were missed in, or modified
since, previous patches. The annotations currently have no meaningful
impact on the LLVM build; however, they are a prerequisite to support an
LLVM Windows DLL (shared library) build.

## Background

This effort is tracked in #109483. Additional context is provided in
[this
discourse](https://discourse.llvm.org/t/psa-annotating-llvm-public-interface/85307),
and documentation for `LLVM_ABI` and related annotations is found in the
LLVM repo
[here](https://github.com/llvm/llvm-project/blob/main/llvm/docs/InterfaceExportAnnotations.rst).

## Overview

The bulk of these changes were generated automatically using the
[Interface Definition Scanner (IDS)](https://github.com/compnerd/ids)
tool, followed formatting with `git clang-format`.

The following manual adjustments were also applied after running IDS:
- Explicitly instantiate `CallLowering::setArgFlags` template method
instances in `CodeGen/GlobalISel/CallLowering.h` and annotate them with
`LLVM_ABI`. These methods are already explicitly instantiated in
`lib/CodeGen/GlobalISel/CallLowering.cpp` but were not `extern` declared
in the header.
- Annotate several explicit template instantiations with
`LLVM_EXPORT_TEMPLATE`.
- Include `llvm/CodeGen/Passes.h` from
`llvm/lib/CodeGen/GlobalMergeFunctions.cpp` to pick up the declaration
of `llvm::createGlobalMergeFuncPass` with the `LLVM_ABI` annotation
(instead of adding `LLVM_ABI` to the function definition in this file)

## Validation

Local builds and tests to validate cross-platform compatibility. This
included llvm, clang, and lldb on the following configurations:

- Windows with MSVC
- Windows with Clang
- Linux with GCC
- Linux with Clang
- Darwin with Clang

Mirror the `getLoopID()` implementation of `LoopInfo` in
`MachineLoopInfo`.

`getLoopID` used `findLoopControlBlock` to detect the special case where
there is a single latch. However, `findLoopControlBlock` returns the
exiting block if the latch is not an exiting block. The middle end
places the `LoopID` metadata on the
latch regardless of if it's an exiting block or not.

I raised this issue in the PR that introduced the `getLoopID()` helper
(https://github.com/llvm/llvm-project/pull/71026#discussion_r2000595214)
and @FreddyLeaf confirmed this is a bug and asked me to help implement a
refinement.

I've mirrored the implementation of `LoopInfo` instead of simply
changing `findLoopControlBlock()` to `findLoopControlBlock()` to keep
the two implementations consistent. The only difference between the two
is that `MachineLoopInfo::getLoopID` initially starts out with a
`MachineBacisBlock` and attempts to retrieve the `BasicBlock` (if it
wasn't for this difference, I would have moved it to `genericLoopInfo`).

I've also updated the test associated with
https://github.com/llvm/llvm-project/pull/71026 (`test5`) that check the
alignment for a loop with a single latch that's not the exit. This test
will fail for the current implementation. I'm not sure if we want to
include this test upstream (it might look out of place after we remove
the 'single-latch-specialization' from `getLoopID()`).

Let me know if you have any comments, @FreddyLeaf !

This relands commit #115111.
Use traditional way to update post dominator tree, i.e. break critical
edge splitting into insert, insert, delete sequence.
When splitting critical edges, the post dominator tree may change its
root node, and `setNewRoot` only works in normal dominator tree...
See

https://github.com/llvm/llvm-project/blob/6c7e5827eda26990e872eb7c3f0d7866ee3c3171/llvm/include/llvm/Support/GenericDomTree.h#L684-L687

Reverts llvm/llvm-project#115111 Causes #119511

Support critical edge splitting in dominator tree updater. Continue the
work in #100856.

Compile time check:
https://llvm-compile-time-tracker.com/compare.php?from=87c35d782795b54911b3e3a91a5b738d4d870e55&to=42b3e5623a9ab4c3648564dc0926b36f3b438a3a&stat=instructions%3Au

This patch also fixed `CodegenPrepare` to preserve loop metadata when
merging blocks.

This fixes issue #102632

Fixes #100115

This reverts commit c5e5088033fed170068d818c54af6862e449b545.

Causes large compile-time regressions.

Summary:
- Remove wrappers in `MachineDominatorTree`.
- Remove `MachineDominatorTree` update code in
`MachineBasicBlock::SplitCriticalEdge`.
- Use `MachineDomTreeUpdater` in passes which call
`MachineBasicBlock::SplitCriticalEdge` and preserve
`MachineDominatorTreeWrapperPass` or CFG analyses.

Commit abea99f65a97248974c02a5544eaf25fc4240056 introduced related
methods in 2014. Now we have SemiNCA based dominator tree in 2017 and
dominator tree updater, the solution adopted here seems a bit outdated.

- Add `MachineLoopAnalysis`.
- Add `MachineLoopPrinterPass`.
- Convert to `MachineLoopInfoWrapperPass` in legacy pass manager.