[flang][driver] Add support for Frontend Plugins

Introducing a plugin API and a simple HelloWorld Plugin example.
This patch adds the `-load` and `-plugin` flags to frontend driver and
the code around using custom frontend actions from within a plugin
shared library object.

It also adds to the Driver-help test to check the help option with the
updated driver flags.

Additionally, the patch creates a plugin-example test to check the
HelloWorld plugin example runs correctly. As part of this, a new CMake
flag (`FLANG_BUILD_EXAMPLES`) is added to allow the example to be built
and for the test to run.

This Plugin API has only been tested on Linux.

Reviewed By: awarzynski

Differential Revision: https://reviews.llvm.org/D106137

1 files changed, 12 insertions, 0 deletions

diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index baa0f32..c16c969 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -199,6 +199,18 @@ static bool ParseFrontendArgs(FrontendOptions &opts, llvm::opt::ArgList &args,
     }
   }
 
+  // Parsing -load <dsopath> option and storing shared object path
+  if (llvm::opt::Arg *a = args.getLastArg(clang::driver::options::OPT_load)) {
+    opts.plugins.push_back(a->getValue());
+  }
+
+  // Parsing -plugin <name> option and storing plugin name and setting action
+  if (const llvm::opt::Arg *a =
+          args.getLastArg(clang::driver::options::OPT_plugin)) {
+    opts.programAction = PluginAction;
+    opts.ActionName = a->getValue();
+  }
+
   opts.outputFile = args.getLastArgValue(clang::driver::options::OPT_o);
   opts.showHelp = args.hasArg(clang::driver::options::OPT_help);
   opts.showVersion = args.hasArg(clang::driver::options::OPT_version);