[all-commits] [llvm/llvm-project] 98595c: [llvm] prepare explicit template instantiations in...

[Andrew Rogers via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 98595cfd6fe1d565821bc6507073a87bbaa7db6f
      https://github.com/llvm/llvm-project/commit/98595cfd6fe1d565821bc6507073a87bbaa7db6f
  Author: Andrew Rogers <andrurogerz at gmail.com>
  Date:   2025-05-20 (Tue, 20 May 2025)

  Changed paths:
    M llvm/include/llvm/CodeGen/MachineBasicBlock.h
    M llvm/include/llvm/CodeGen/MachineDomTreeUpdater.h
    M llvm/include/llvm/CodeGen/MachineDominators.h
    A llvm/include/llvm/CodeGen/MachineFunctionAnalysisManager.h
    M llvm/include/llvm/CodeGen/MachinePassManager.h
    M llvm/include/llvm/Support/GenericDomTree.h
    M llvm/lib/CodeGen/MachinePassManager.cpp

  Log Message:
  -----------
  [llvm] prepare explicit template instantiations in llvm/CodeGen for DLL export annotations (#140653)

## Purpose

This patch prepares the llvm/CodeGen library for public interface
annotations in support of an LLVM Windows DLL (shared library) build,
tracked in #109483. The purpose of this patch is to make the upcoming
codemod of this library more straight-forward. It is not expected to
impact any functionality.

The `LLVM_ABI` annotations will be added in a subsequent patch. These
changes are required to build with visibility annotations using Clang
and gcc on Linux/Darwin/etc; Windows DLL can build fine without them.

## Overview
This PR does four things in preparation for adding `LLVM_ABI`
annotations to llvm/CodeGen:
1. Explicitly include `Machine.h` and `Function.h` headers from
`MachinePassManager.cpp` so that `Function` and `Machine` types are
available for the instantiations of `InnerAnalysisManagerProxy`. Without
this change, Clang only will only export one of the templates after
visibility annotations are added to them. Unclear if this is a Clang bug
or expected behavior, but this change avoids the issue and should be
harmless.
2. Refactor the definition of `MachineFunctionAnalysisManager` to its
own header file. Without this change, it is not possible to add
visibility annotations to the declaration with causing gcc to produce
`-Wattribute` warnings.
3. Remove the redundant specialization of the
`DominatorTreeBase<MachineBasicBlock, false>::addRoot` method. The
specialization is the same as implemented in `DominatorTreeBase` so
should be unnecessary. Without this change, it is not possible to
annotate the subsequent instantiations of `DominatorTreeBase` in the
header file without gcc producing `-Wattribute` warnings. Mark
unspecialized `addRoot` as `inline` to match the removed specialized
version.
4. Move the explicit instantiations of the `GenericDomTreeUpdater`
template earlier in the header file. These need to appear before being
used in the `MachineDomTreeUpdater` class definition or gcc will produce
warnings once visibility annotations are added.

## Background

The LLVM Windows DLL effort is tracked in #109483. Additional context is
provided in [this
discourse](https://discourse.llvm.org/t/psa-annotating-llvm-public-interface/85307).

Clang and gcc handle visibility attributes on explicit template
instantiations a bit differently; gcc is pickier and generates
`-Wattribute` warnings when an explicit instantiation with a visibility
annotation appears after the type has already appeared in the
translation unit. These warnings can be avoided by moving explicit
template instantiations so they always appear first.

## 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



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