[examples][ORC] Add a new example showing the ORCv2 removable code APIs.

llvm/examples/OrcV2Examples/CMakeLists.txt

@@ -1,4 +1,5 @@
 add_subdirectory(LLJITDumpObjects)
+add_subdirectory(LLJITRemovableCode)
 add_subdirectory(LLJITWithCustomObjectLinkingLayer)
 add_subdirectory(LLJITWithExecutorProcessControl)
 add_subdirectory(LLJITWithGDBRegistrationListener)

llvm/examples/OrcV2Examples/LLJITRemovableCode/CMakeLists.txt

@@ -0,0 +1,14 @@
+set(LLVM_LINK_COMPONENTS
+  Core
+  ExecutionEngine
+  IPO
+  IRReader
+  OrcJIT
+  ScalarOpts
+  Support
+  nativecodegen
+  )
+
+add_llvm_example(LLJITRemovableCode
+  LLJITRemovableCode.cpp
+  )

llvm/examples/OrcV2Examples/LLJITRemovableCode/LLJITRemovableCode.cpp

@@ -0,0 +1,137 @@
+//===--------- LLJITRemovableCode.cpp -- LLJIT with Code Removal ----------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// In this example we will use an the resource management APIs to transfer
+// ownership of modules, remove modules from a JITDylib, and then a whole
+// JITDylib from the ExecutionSession.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ExecutionEngine/Orc/LLJIT.h"
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/InitLLVM.h"
+#include "llvm/Support/TargetSelect.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/IPO.h"
+#include "llvm/Transforms/Scalar.h"
+
+#include "../ExampleModules.h"
+
+using namespace llvm;
+using namespace llvm::orc;
+
+ExitOnError ExitOnErr;
+
+// Example IR modules.
+//
+// We will use a few modules containing no-op functions to demonstrate the code
+// removal APIs.
+
+const llvm::StringRef FooMod =
+    R"(
+  define void @foo() {
+  entry:
+    ret void
+  }
+)";
+
+const llvm::StringRef BarMod =
+    R"(
+  define void @bar() {
+  entry:
+    ret void
+  }
+)";
+
+const llvm::StringRef BazMod =
+    R"(
+  define void @baz() {
+  entry:
+    ret void
+  }
+)";
+
+int main(int argc, char *argv[]) {
+  // Initialize LLVM.
+  InitLLVM X(argc, argv);
+
+  InitializeNativeTarget();
+  InitializeNativeTargetAsmPrinter();
+
+  ExitOnErr.setBanner(std::string(argv[0]) + ": ");
+
+  // (1) Create LLJIT instance.
+  auto J = ExitOnErr(LLJITBuilder().create());
+
+  // (2) Create a new JITDylib to use for this example.
+  auto &JD = ExitOnErr(J->createJITDylib("JD"));
+
+  // (3) Add the 'foo' module with no explicit resource tracker. The resources
+  // for 'foo' will be tracked by the default tracker for JD. We will not be
+  // able to free it separately, but its resources will still be freed when we
+  // clear or remove JD.
+  ExitOnErr(J->addIRModule(JD, ExitOnErr(parseExampleModule(FooMod, "foo"))));
+
+  // (4) Create a tracker for the module 'bar' and use it to add that module.
+  auto BarRT = JD.createResourceTracker();
+  ExitOnErr(
+      J->addIRModule(BarRT, ExitOnErr(parseExampleModule(BarMod, "bar"))));
+
+  // (5) Create a tracker for the module 'baz' and use it to add that module.
+  auto BazRT = JD.createResourceTracker();
+  ExitOnErr(
+      J->addIRModule(BazRT, ExitOnErr(parseExampleModule(BazMod, "baz"))));
+
+  // (6) Print out the symbols in their initial state:
+  auto PrintSymbol = [&](StringRef Name) {
+    dbgs() << Name << " = ";
+    if (auto Sym = J->lookup(JD, Name))
+      dbgs() << formatv("{0:x}\n", Sym->getAddress());
+    else
+      dbgs() << "error: " << toString(Sym.takeError()) << "\n";
+  };
+
+  dbgs() << "Initially:\n";
+  PrintSymbol("foo");
+  PrintSymbol("bar");
+  PrintSymbol("baz");
+
+  // (7) Reset BazRT. This will implicitly transfer tracking of module baz to
+  // JD's default resource tracker.
+  dbgs() << "After implicitly transferring ownership of baz to JD's default "
+            "tracker:\n";
+  BazRT = nullptr;
+  PrintSymbol("foo");
+  PrintSymbol("bar");
+  PrintSymbol("baz");
+
+  // (8) Remove BarRT. This should remove the bar symbol.
+  dbgs() << "After removing bar (lookup for bar should yield a missing symbol "
+            "error):\n";
+  ExitOnErr(BarRT->remove());
+  PrintSymbol("foo");
+  PrintSymbol("bar");
+  PrintSymbol("baz");
+
+  // (9) Clear JD. This should remove all symbols currently in the JITDylib.
+  dbgs() << "After clearing JD (lookup should yield missing symbol errors for "
+            "all symbols):\n";
+  ExitOnErr(JD.clear());
+  PrintSymbol("foo");
+  PrintSymbol("bar");
+  PrintSymbol("baz");
+
+  // (10) Remove JD from the ExecutionSession. JD can no longer be used.
+  dbgs() << "Removing JD.\n";
+  ExitOnErr(J->getExecutionSession().removeJITDylib(JD));
+
+  dbgs() << "done.\n";
+
+  return 0;
+}