[docs][NewPM] Move pass plugin documentation into existing new PM docs

Reviewed By: awarzynski, asbirlea

Differential Revision: https://reviews.llvm.org/D136626

llvm/docs/NewPassManager.rst

@@ -179,6 +179,11 @@ sanitizer) passes to various parts of the pipeline.
 ``AMDGPUTargetMachine::registerPassBuilderCallbacks()`` is an example of a
 backend adding passes to various parts of the pipeline.
 
+Pass plugins can also add passes into default pipelines. Different tools have
+different ways of loading dynamic pass plugins. For example, ``opt
+-load-pass-plugin=path/to/plugin.so`` loads a pass plugin into ``opt``. For
+information on writing a pass plugin, see :doc:`WritingAnLLVMNewPMPass`.
+
 Using Analyses
 ==============
 

llvm/docs/WritingAnLLVMNewPMPass.rst

@@ -232,3 +232,58 @@ function. Required passes will still be run on ``optnone`` functions.
 
 For more implementation details, see
 ``PassInstrumentation::runBeforePass()``.
+
+Registering passes as plugins
+-----------------------------
+
+LLVM provides a mechanism to register pass plugins within various tools like
+``clang`` or ``opt``. A pass plugin can add passes to default optimization
+pipelines or to be manually run via tools like ``opt``.  For more information,
+see :doc:`NewPassManager`.
+
+Create a CMake project at the root of the repo alongside
+other projects.  This project must contain the following minimal
+``CMakeLists.txt``:
+
+.. code-block:: cmake
+
+    add_llvm_pass_plugin(MyPassName source.cpp)
+
+See the definition of ``add_llvm_pass_plugin`` for more CMake details.
+
+The pass must provide at least one of two entry points for the new pass manager,
+one for static registration and one for dynamically loaded plugins:
+
+- ``llvm::PassPluginLibraryInfo get##Name##PluginInfo();``
+- ``extern "C" ::llvm::PassPluginLibraryInfo llvmGetPassPluginInfo() LLVM_ATTRIBUTE_WEAK;``
+
+Pass plugins are compiled and linked dynamically by default. Setting
+``LLVM_${NAME}_LINK_INTO_TOOLS`` to ``ON`` turns the project into a statically
+linked extension.
+
+For an in-tree example, see ``llvm/examples/Bye/``.
+
+To make ``PassBuilder`` aware of statically linked pass plugins:
+
+.. code-block:: c++
+
+    // Declare plugin extension function declarations.
+    #define HANDLE_EXTENSION(Ext) llvm::PassPluginLibraryInfo get##Ext##PluginInfo();
+    #include "llvm/Support/Extension.def"
+
+    ...
+
+    // Register plugin extensions in PassBuilder.
+    #define HANDLE_EXTENSION(Ext) get##Ext##PluginInfo().RegisterPassBuilderCallbacks(PB);
+    #include "llvm/Support/Extension.def"
+
+To make ``PassBuilder`` aware of dynamically linked pass plugins:
+
+.. code-block:: c++
+
+    // Load plugin dynamically.
+    auto Plugin = PassPlugin::Load(PathToPlugin);
+    if (!Plugin)
+      report_error();
+    // Register plugin extensions in PassBuilder.
+    Plugin.registerPassBuilderCallbacks(PB);

llvm/docs/WritingAnLLVMPass.rst

@@ -1183,51 +1183,6 @@ implement ``releaseMemory`` to, well, release the memory allocated to maintain
 this internal state.  This method is called after the ``run*`` method for the
 class, before the next call of ``run*`` in your pass.
 
-Building pass plugins
-=====================
-
-As an alternative to using ``PLUGIN_TOOL``, LLVM provides a mechanism to
-automatically register pass plugins within ``clang``, ``opt`` and ``bugpoint``.
-One first needs to create an independent project and add it to either ``tools/``
-or, using the MonoRepo layout, at the root of the repo alongside other projects.
-This project must contain the following minimal ``CMakeLists.txt``:
-
-.. code-block:: cmake
-
-    add_llvm_pass_plugin(Name source0.cpp)
-
-The pass must provide two entry points for the new pass manager, one for static
-registration and one for dynamically loaded plugins:
-
-- ``llvm::PassPluginLibraryInfo get##Name##PluginInfo();``
-- ``extern "C" ::llvm::PassPluginLibraryInfo llvmGetPassPluginInfo() LLVM_ATTRIBUTE_WEAK;``
-
-Pass plugins are compiled and link dynamically by default, but it's
-possible to set the following variables to change this behavior:
-
-- ``LLVM_${NAME}_LINK_INTO_TOOLS``, when set to ``ON``, turns the project into
-  a statically linked extension
-
-
-When building a tool that uses the new pass manager, one can use the following snippet to
-include statically linked pass plugins:
-
-.. code-block:: c++
-
-    // fetch the declaration
-    #define HANDLE_EXTENSION(Ext) llvm::PassPluginLibraryInfo get##Ext##PluginInfo();
-    #include "llvm/Support/Extension.def"
-
-    [...]
-
-    // use them, PB is an llvm::PassBuilder instance
-    #define HANDLE_EXTENSION(Ext) get##Ext##PluginInfo().RegisterPassBuilderCallbacks(PB);
-    #include "llvm/Support/Extension.def"
-
-
-
-
-
 Registering dynamically loaded passes
 =====================================