Generalize the pass registration mechanism used by Polly to any third-party tool

There's quite a lot of references to Polly in the LLVM CMake codebase. However
the registration pattern used by Polly could be useful to other external
projects: thanks to that mechanism it would be possible to develop LLVM
extension without touching the LLVM code base.

This patch has two effects:

1. Remove all code specific to Polly in the llvm/clang codebase, replaicing it
   with a generic mechanism

2. Provide a generic mechanism to register compiler extensions.

A compiler extension is similar to a pass plugin, with the notable difference
that the compiler extension can be configured to be built dynamically (like
plugins) or statically (like regular passes).

As a result, people willing to add extra passes to clang/opt can do it using a
separate code repo, but still have their pass be linked in clang/opt as built-in
passes.

Differential Revision: https://reviews.llvm.org/D61446

4 files changed, 49 insertions, 40 deletions

diff --git a/polly/lib/CMakeLists.txt b/polly/lib/CMakeLists.txt
index 5bbc4dcf109..e76d6039ad5 100644
--- a/polly/lib/CMakeLists.txt
+++ b/polly/lib/CMakeLists.txt
@@ -23,7 +23,7 @@ endif ()
 
 # Use an object-library to add the same files to multiple libs without requiring
 # the sources them to be recompiled for each of them.
-add_library(PollyCore OBJECT
+add_llvm_pass_plugin(Polly
   Analysis/DependenceInfo.cpp
   Analysis/PolyhedralInfo.cpp
   Analysis/ScopDetection.cpp
@@ -70,13 +70,13 @@ add_library(PollyCore OBJECT
   Transform/ScopInliner.cpp
   ${POLLY_HEADER_FILES}
   )
-set_target_properties(PollyCore PROPERTIES FOLDER "Polly")
+set_target_properties(obj.Polly PROPERTIES FOLDER "Polly")
+set_target_properties(Polly PROPERTIES FOLDER "Polly")
 
 # Create the library that can be linked into LLVM's tools and Polly's unittests.
 # It depends on all library it needs, such that with
 # LLVM_POLLY_LINK_INTO_TOOLS=ON, its dependencies like PollyISL are linked as
 # well.
-add_polly_library(Polly $<TARGET_OBJECTS:PollyCore>)
 target_link_libraries(Polly PUBLIC
   ${ISL_TARGET}
 )
@@ -124,6 +124,9 @@ else ()
     LLVMTarget
     LLVMVectorize
     )
+
+    # Polly-ACC requires the NVPTX target to be present in the executable it is linked to
+    set_property(TARGET bugpoint APPEND PROPERTY LINK_LIBRARIES LLVMTarget)
 endif ()
 
 # Create a loadable module Polly.so that can be loaded using
@@ -134,8 +137,8 @@ if (MSVC)
   set_target_properties(LLVMPolly PROPERTIES FOLDER "Polly")
 else ()
   add_polly_loadable_module(LLVMPolly
-    Polly.cpp
-    $<TARGET_OBJECTS:PollyCore>
+    Plugin/Polly.cpp
+    $<TARGET_OBJECTS:obj.Polly>
   )
 
   # Only add the dependencies that are not part of LLVM. The latter are assumed
@@ -159,5 +162,5 @@ endif ()
 
 if (TARGET intrinsics_gen)
   # Check if we are building as part of an LLVM build
-  add_dependencies(PollyCore intrinsics_gen)
+  add_dependencies(obj.Polly intrinsics_gen)
 endif()
diff --git a/polly/lib/Plugin/Polly.cpp b/polly/lib/Plugin/Polly.cpp
new file mode 100644
index 00000000000..f567d37c07e
--- /dev/null
+++ b/polly/lib/Plugin/Polly.cpp
@@ -0,0 +1,20 @@
+//===---------- Polly.cpp - Initialize the Polly Module -------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//===----------------------------------------------------------------------===//
+
+#include "polly/RegisterPasses.h"
+#include "llvm/PassRegistry.h"
+#include "llvm/Passes/PassPlugin.h"
+
+// Pass Plugin Entrypoints
+
+extern "C" LLVM_ATTRIBUTE_WEAK ::llvm::PassPluginLibraryInfo
+llvmGetPassPluginInfo() {
+  return getPollyPluginInfo();
+}
diff --git a/polly/lib/Polly.cpp b/polly/lib/Polly.cpp
deleted file mode 100644
index e6bae931fc5..00000000000
--- a/polly/lib/Polly.cpp
+++ /dev/null
@@ -1,29 +0,0 @@
-//===---------- Polly.cpp - Initialize the Polly Module -------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-//
-//===----------------------------------------------------------------------===//
-
-#include "polly/RegisterPasses.h"
-#include "llvm/PassRegistry.h"
-
-namespace {
-
-/// Initialize Polly passes when library is loaded.
-///
-/// We use the constructor of a statically declared object to initialize the
-/// different Polly passes right after the Polly library is loaded. This ensures
-/// that the Polly passes are available e.g. in the 'opt' tool.
-class StaticInitializer {
-public:
-  StaticInitializer() {
-    llvm::PassRegistry &Registry = *llvm::PassRegistry::getPassRegistry();
-    polly::initializePollyPasses(Registry);
-  }
-};
-static StaticInitializer InitializeEverything;
-} // end of anonymous namespace.
diff --git a/polly/lib/Support/RegisterPasses.cpp b/polly/lib/Support/RegisterPasses.cpp
index 1d31db5e984..4ceca070b37 100644
--- a/polly/lib/Support/RegisterPasses.cpp
+++ b/polly/lib/Support/RegisterPasses.cpp
@@ -235,6 +235,23 @@ static cl::opt<bool> EnablePruneUnprofitable(
     cl::desc("Bail out on unprofitable SCoPs before rescheduling"), cl::Hidden,
     cl::init(true), cl::cat(PollyCategory));
 
+namespace {
+
+/// Initialize Polly passes when library is loaded.
+///
+/// We use the constructor of a statically declared object to initialize the
+/// different Polly passes right after the Polly library is loaded. This ensures
+/// that the Polly passes are available e.g. in the 'opt' tool.
+class StaticInitializer {
+public:
+  StaticInitializer() {
+    llvm::PassRegistry &Registry = *llvm::PassRegistry::getPassRegistry();
+    polly::initializePollyPasses(Registry);
+  }
+};
+static StaticInitializer InitializeEverything;
+} // end of anonymous namespace.
+
 namespace polly {
 void initializePollyPasses(PassRegistry &Registry) {
   initializeCodeGenerationPass(Registry);
@@ -690,7 +707,7 @@ parseTopLevelPipeline(ModulePassManager &MPM,
   return true;
 }
 
-void RegisterPollyPasses(PassBuilder &PB) {
+void registerPollyPasses(PassBuilder &PB) {
   PB.registerAnalysisRegistrationCallback(registerFunctionAnalyses);
   PB.registerPipelineParsingCallback(parseFunctionPipeline);
   PB.registerPipelineParsingCallback(parseScopPipeline);
@@ -702,9 +719,7 @@ void RegisterPollyPasses(PassBuilder &PB) {
 }
 } // namespace polly
 
-// Plugin Entrypoint:
-extern "C" ::llvm::PassPluginLibraryInfo LLVM_ATTRIBUTE_WEAK
-llvmGetPassPluginInfo() {
+llvm::PassPluginLibraryInfo getPollyPluginInfo() {
   return {LLVM_PLUGIN_API_VERSION, "Polly", LLVM_VERSION_STRING,
-          polly::RegisterPollyPasses};
+          polly::registerPollyPasses};
 }