[Flang] Allow registering plugin extensions with the pass builder.

[mnadeem]

Summary

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. Projects like Polly can be used this way by
adding -DLLVM_POLLY_LINK_INTO_TOOLS=ON to the cmake command.

The changes in this patch makes the PassBuilder in Flang aware of statically
linked pass plugins, see the documentation for more details:
https://github.com/llvm/llvm-project/blob/main/llvm/docs/WritingAnLLVMNewPMPass.rst#id21

[awarzynski]

Hey @mnadeem , thanks for sending this!

1. Could you add a test? I would hope that you can re-use Bye, similarly to https://reviews.llvm.org/D129156.
2. Could you document how to use this?

[mnadeem]

In D137673#3916647, @awarzynski wrote:

Hey @mnadeem , thanks for sending this!

1. Could you add a test? I would hope that you can re-use Bye, similarly to https://reviews.llvm.org/D129156.
2. Could you document how to use this?

@awarzynski
I'll work on adding a test. I have updated the summary of this revision, would that suffice as documentation?

[mnadeem]

Added a test and did the relevant test config changes.

[awarzynski]

Thanks for the updates!

In D137673#3917846, @mnadeem wrote:

I have updated the summary of this revision, would that suffice as documentation?

I was hoping for a note in https://github.com/llvm/llvm-project/blob/main/flang/docs/FlangDriver.md#frontend-driver-plugins,. Even if it was just to make folks aware that from now on the behavior in Flang can be changed with LLVM_${NAME}_LINK_INTO_TOOLS. Because this is basically what this patch does, doesn't it? This is fine too :)

flang/test/Driver/pass-plugin.f90

4

[nit] More specifically, when https://reviews.llvm.org/D129156. is merged, right?

flang/docs/FlangDriver.md

 shared object which is then loaded using the `-fpass-plugin` option.
 
 ```
 flang-new -fpass-plugin=/path/to/plugin.so <file.f90>
 ```
 
 This option is available in both the compiler driver and the frontend driver.
 Note that LLVM plugins are not officially supported on Windows.
+
+## LLVM Pass Extensions
+
+Pass extensions are similar to plugins, except that they can also be linked
+statically. Setting `-DLLVM_${NAME}_LINK_INTO_TOOLS` to `ON` in the cmake
+command turns the project into a statically linked extension. An example would
+be Polly, e.g., using `-DLLVM_POLLY_LINK_INTO_TOOLS=ON` would link Polly passes
+into `flang-new` as built-in middle-end passes.
+
+See the
+[`WritingAnLLVMNewPMPass`](https://llvm.org/docs/WritingAnLLVMNewPMPass.html#id9)
+documentation for more details.

flang/docs/ReleaseNotes.md

 release notes for a specific release, please see the [releases
 page](https://llvm.org/releases/).
 
 ## Major New Features
 
 * Flang now supports loading LLVM pass plugins with the `-fpass-plugin` option
   which is also available in clang. The option mimics the behavior of the
   corresponding option in clang and has the same capabilities and limitations.
+* Flang also supports statically linked LLVM pass extensions. Projects can be
+  linked statically into `flang-new` if the cmake command includes
+  `-DLLVM_${NAME}_LINK_INTO_TOOLS=ON`. This behavior is also similar to clang.
 
 ## Bug Fixes
 
 ## Non-comprehensive list of changes in this release
 * The bash wrapper script, `flang`, is renamed as `flang-to-external-fc`.
 * In contrast to Clang, Flang will not default to using `-fpie` when linking
   executables. This is only a temporary solution and the goal is to align with
   Clang in the near future. First, however, the frontend driver needs to be

flang/lib/Frontend/CMakeLists.txt

add_flang_library(flangFrontend
   MLIRLLVMToLLVMIRTranslation
   MLIRSCFToControlFlow
   MLIRTargetLLVMIRImport
   ${dialect_libs}
 
   LINK_COMPONENTS
   Passes
   Analysis
+  Extensions
   IRReader
   Option
   Support
   Target
   FrontendOpenACC
   FrontendOpenMP
 )
 

flang/lib/Frontend/FrontendActions.cpp

 #include "llvm/Passes/StandardInstrumentations.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Target/TargetMachine.h"
 #include <memory>
 
 using namespace Fortran::frontend;
 
+// Declare plugin extension function declarations.
+#define HANDLE_EXTENSION(Ext)                                                  \
+  llvm::PassPluginLibraryInfo get##Ext##PluginInfo();
+#include "llvm/Support/Extension.def"
+
 //===----------------------------------------------------------------------===//
 // Custom BeginSourceFileAction
 //===----------------------------------------------------------------------===//
 
 bool PrescanAction::beginSourceFileAction() { return runPrescan(); }
 
 bool PrescanAndParseAction::beginSourceFileAction() {
   return runPrescan() && runParse();
for (auto &pluginFile : opts.LLVMPassPlugins) {
     auto passPlugin = llvm::PassPlugin::Load(pluginFile);
     if (passPlugin) {
       passPlugin->registerPassBuilderCallbacks(pb);
     } else {
       diags.Report(clang::diag::err_fe_unable_to_load_plugin)
           << pluginFile << passPlugin.takeError();
     }
   }
+  // Register static plugin extensions.
+#define HANDLE_EXTENSION(Ext)                                                  \
+  get##Ext##PluginInfo().RegisterPassBuilderCallbacks(pb);
+#include "llvm/Support/Extension.def"
 
   // Register all the basic analyses with the managers.
   pb.registerModuleAnalyses(mam);
   pb.registerCGSCCAnalyses(cgam);
   pb.registerFunctionAnalyses(fam);
   pb.registerLoopAnalyses(lam);
   pb.crossRegisterProxies(lam, fam, cgam, mam);
 

flang/test/CMakeLists.txt

 # Test runner infrastructure for Flang. This configures the Flang test trees
 # for use by Lit, and delegates to LLVM's lit test handlers.
 add_subdirectory(lib)
 
 llvm_canonicalize_cmake_booleans(
   FLANG_BUILD_EXAMPLES
   FLANG_STANDALONE_BUILD
+  LLVM_BYE_LINK_INTO_TOOLS
   LLVM_ENABLE_PLUGINS
 )
 
 set(FLANG_TOOLS_DIR ${FLANG_BINARY_DIR}/bin)
 
 # FIXME In out-of-tree builds, "SHLIBDIR" is undefined and passing it to
 # `configure_lit_site_cfg` leads to a configuration error. This is currently
 # only required by plugins/examples, which are not supported in out-of-tree

flang/test/Driver/pass-plugin.f90

-! Verify that the plugin passed to -fpass-plugin is loaded and run
+! Verify that the static and dynamically loaded pass plugins work as expected.
 
 ! UNSUPPORTED: system-windows
 
 ! REQUIRES: plugins, shell, examples
 
-! RUN: %flang -S %s -fpass-plugin=%llvmshlibdir/Bye%pluginext -Xflang -fdebug-pass-manager -o /dev/null 2>&1 | FileCheck %s
-! RUN: %flang_fc1 -S %s -fpass-plugin=%llvmshlibdir/Bye%pluginext -fdebug-pass-manager -o /dev/null 2>&1 | FileCheck %s
+! RUN: %flang -S %s %loadbye -Xflang -fdebug-pass-manager -o /dev/null \
+! RUN: 2>&1 | FileCheck %s
+
+! RUN: %flang_fc1 -S %s %loadbye -fdebug-pass-manager -o /dev/null \
+! RUN: 2>&1 | FileCheck %s
+
 
 ! CHECK: Running pass: {{.*}}Bye on empty_
 
 subroutine empty
 end subroutine empty

flang/test/lit.cfg.py

 # If the flang examples are built, add examples to the config
 if config.flang_examples:
     config.available_features.add('examples')
 
 # Plugins (loadable modules)
 if config.has_plugins:
     config.available_features.add('plugins')
 
+if config.linked_bye_extension:
+    config.substitutions.append(('%loadbye', ''))
+else:
+    config.substitutions.append(('%loadbye',
+                                 '-fpass-plugin={}/Bye{}'.format(config.llvm_shlib_dir,
+                                                                 config.llvm_plugin_ext)))
+
 # test_source_root: The root path where tests are located.
 config.test_source_root = os.path.dirname(__file__)
 
 # test_exec_root: The root path where tests should be run.
 config.test_exec_root = os.path.join(config.flang_obj_root, 'test')
 
 # Tweak the PATH to include the tools dir.
 llvm_config.with_environment('PATH', config.flang_tools_dir, append_path=True)

flang/test/lit.site.cfg.py.in

 config.flang_tools_dir = lit_config.substitute("@FLANG_TOOLS_DIR@")
 config.flang_intrinsic_modules_dir = "@FLANG_INTRINSIC_MODULES_DIR@"
 config.flang_llvm_tools_dir = "@CMAKE_BINARY_DIR@/bin"
 config.flang_lib_dir = "@CMAKE_BINARY_DIR@/lib"
 config.flang_examples = @FLANG_BUILD_EXAMPLES@
 config.python_executable = "@PYTHON_EXECUTABLE@"
 config.flang_standalone_build = @FLANG_STANDALONE_BUILD@
 config.has_plugins = @LLVM_ENABLE_PLUGINS@
+config.linked_bye_extension = @LLVM_BYE_LINK_INTO_TOOLS@
 config.cc = "@CMAKE_C_COMPILER@"
 config.targets_to_build = "@TARGETS_TO_BUILD@"
 
 import lit.llvm
 lit.llvm.initialize(lit_config, config)
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@FLANG_SOURCE_DIR@/test/lit.cfg.py")