[CIR] Build out AST consumer patterns to reach the entry point into CIRGen

Build out the necessary infrastructure for the main entry point into
ClangIR generation -- CIRGenModule. A set of boilerplate classes exist
to facilitate this -- CIRGenerator, CIRGenAction, EmitCIRAction and
CIRGenConsumer. These all mirror the corresponding types from LLVM
generation by Clang's CodeGen.

The main entry point to CIR generation is
`CIRGenModule::buildTopLevelDecl`. It is currently just an empty
function. We've added a test to ensure that the pipeline reaches this
point and doesn't fail, but does nothing else. This will be removed in
one of the subsequent patches that'll add basic `cir.func` emission.

This patch also re-adds `-emit-cir` to the driver. lib/Driver/Driver.cpp
requires that a driver flag exists to facilirate the selection of the
right actions for the driver to create. Without a driver flag you get
the standard behaviors of `-S`, `-c`, etc. If we want to emit CIR IR
and, eventually, bytecode we'll need a driver flag to force this. This
is why `-emit-llvm` is a driver flag. Notably, `-emit-llvm-bc` as a cc1
flag doesn't ever do the right thing. Without a driver flag it is
incorrectly ignored and an executable is emitted. With `-S` a file named
`something.s` is emitted which actually contains bitcode.

Reviewers: AaronBallman, MaskRay, bcardosolopes

Reviewed By: bcardosolopes, AaronBallman

Pull Request: https://github.com/llvm/llvm-project/pull/91007

1 files changed, 16 insertions, 0 deletions

diff --git a/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp b/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
index 7476b10..60fde03 100644
--- a/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
+++ b/clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
@@ -31,6 +31,11 @@
 #include "llvm/Support/BuryPointer.h"
 #include "llvm/Support/DynamicLibrary.h"
 #include "llvm/Support/ErrorHandling.h"
+
+#if CLANG_ENABLE_CIR
+#include "clang/CIR/FrontendAction/CIRGenAction.h"
+#endif
+
 using namespace clang;
 using namespace llvm::opt;
 
@@ -42,6 +47,13 @@ CreateFrontendBaseAction(CompilerInstance &CI) {
   StringRef Action("unknown");
   (void)Action;
 
+  unsigned UseCIR = CI.getFrontendOpts().UseClangIRPipeline;
+  frontend::ActionKind Act = CI.getFrontendOpts().ProgramAction;
+  bool EmitsCIR = Act == EmitCIR;
+
+  if (!UseCIR && EmitsCIR)
+    llvm::report_fatal_error("-emit-cir and only valid when using -fclangir");
+
   switch (CI.getFrontendOpts().ProgramAction) {
   case ASTDeclList:            return std::make_unique<ASTDeclListAction>();
   case ASTDump:                return std::make_unique<ASTDumpAction>();
@@ -54,7 +66,11 @@ CreateFrontendBaseAction(CompilerInstance &CI) {
   case EmitAssembly:           return std::make_unique<EmitAssemblyAction>();
   case EmitBC:                 return std::make_unique<EmitBCAction>();
   case EmitCIR:
+#if CLANG_ENABLE_CIR
+    return std::make_unique<::cir::EmitCIRAction>();
+#else
     llvm_unreachable("CIR suppport not built into clang");
+#endif
   case EmitHTML:               return std::make_unique<HTMLPrintAction>();
   case EmitLLVM:               return std::make_unique<EmitLLVMAction>();
   case EmitLLVMOnly:           return std::make_unique<EmitLLVMOnlyAction>();