[llvm] [CodeGen] Expose the extensibility of PassConfig to plugins (PR #139059)

[Stefan Gränitz via llvm-commits]

================
@@ -0,0 +1,114 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 "Plugin/CodeGenTestPass.h"
+
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/Config/config.h"
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/MC/TargetRegistry.h"
+#include "llvm/Support/DynamicLibrary.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/Target/TargetMachine.h"
+
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+void anchor() {}
+
+std::optional<std::string> libPath(const std::string &Name) {
+  const auto &Argvs = testing::internal::GetArgvs();
+  if (Argvs.size() <= 0)
+    return std::nullopt;
+  void *Ptr = (void *)(intptr_t)anchor;
+  std::string Path = sys::fs::getMainExecutable(Argvs[0].c_str(), Ptr);
+  SmallString<256> Buf{sys::path::parent_path(Path)};
+  sys::path::append(Buf, (Name + LLVM_PLUGIN_EXT).c_str());
+  return std::string(Buf.str());
+}
+} // namespace
+
+namespace llvm {
+class CGPluginTests : public testing::Test {
+protected:
+  static void SetUpTestCase() {
+    InitializeAllTargetMCs();
+    InitializeAllTargetInfos();
+    InitializeAllTargets();
+  }
+};
+} // namespace llvm
+
+TEST_F(CGPluginTests, LoadPlugin) {
+#if !defined(LLVM_ENABLE_PLUGINS)
+  // Skip the test if plugins are disabled.
+  GTEST_SKIP();
+#endif
+
+  auto PluginPath = libPath("CGTestPlugin");
+  ASSERT_TRUE(PluginPath.has_value());
+  ASSERT_NE("", PluginPath);
+
+  ASSERT_EQ(TargetMachine::TargetPassConfigCallbacks->size(), 0u);
+  std::string Error;
+  auto Library =
+      sys::DynamicLibrary::getPermanentLibrary(PluginPath->c_str(), &Error);
+  ASSERT_TRUE(Library.isValid()) << Error;
+  ASSERT_EQ(TargetMachine::TargetPassConfigCallbacks->size(), 1u);
+  TargetMachine::TargetPassConfigCallbacks->clear();
+}
+
+TEST_F(CGPluginTests, ExecuteCallback) {
+#if !defined(LLVM_ENABLE_PLUGINS)
+  // Skip the test if plugins are disabled.
+  GTEST_SKIP();
+#endif
+
+  volatile bool CallbackExecuted = false;
+  volatile bool MPassExecuted = false;
+
+  ASSERT_EQ(TargetMachine::TargetPassConfigCallbacks->size(), 0u);
+  TargetMachine::registerTargetPassConfigCallback(
+      [&](auto &TM, auto &PM, auto *TPC) {
+        CallbackExecuted = true;
+        TPC->insertPass(&GCLoweringID, &CodeGenTest::ID);
+      });
+  ASSERT_EQ(TargetMachine::TargetPassConfigCallbacks->size(), 1u);
+
+  CodeGenTest::RunCallback = [&] { MPassExecuted = true; };
+
+  TargetOptions Options;
+  std::unique_ptr<MCContext> MCC;
+  for (auto T : TargetRegistry::targets()) {
+    if (!T.hasTargetMachine())
+      continue;
+    Triple TT{T.getName(), "", ""};
+    auto *TM = T.createTargetMachine(TT, "", "", Options, std::nullopt,
+                                     std::nullopt, CodeGenOptLevel::Default);
+    ASSERT_TRUE(TM);
+
+    legacy::PassManager PM;
+    MCC.reset(new MCContext(TT, TM->getMCAsmInfo(), TM->getMCRegisterInfo(),
+                            TM->getMCSubtargetInfo()));
+    auto *PtrMCC = MCC.get();
+    CallbackExecuted = false;
+    MPassExecuted = false;
+    if (TM->addPassesToEmitMC(PM, PtrMCC, outs()) == true)
+      continue;
+    ASSERT_TRUE(CallbackExecuted) << T.getName() << " callback failed";
+    ASSERT_TRUE(MPassExecuted) << T.getName() << " MachinePass failed";
+  }
+
+  TargetMachine::TargetPassConfigCallbacks->clear();
+}
----------------
weliveindetail wrote:

Thanks! There will be a lot of LLVM configurations where this will likely fail (Windows, AIX, etc.) and we must figure out where it works and where not. Usually we make a good guess and go through a number of revert/reland cycles. It will be a pain though to do this with the whole patch and it would add unnecessary fuzz to the history for a lot of code. So, why not restrict it to the configuration that you are developing on and iterate from there? Iterations will only touch the test then.

@Tcc100 I guess this will be a good candidate. Is the test running for you like that?
```
# REQUIRES: native && system-linux && llvm-dylib
```

https://github.com/llvm/llvm-project/pull/139059