[clang] Add -fc++-abi= flag for specifying which C++ ABI to use

This implements the flag proposed in RFC http://lists.llvm.org/pipermail/cfe-dev/2020-August/066437.html.

The goal is to add a way to override the default target C++ ABI through
a compiler flag. This makes it easier to test and transition between different
C++ ABIs through compile flags rather than build flags.

In this patch:
- Store `-fc++-abi=` in a LangOpt. This isn't stored in a
  CodeGenOpt because there are instances outside of codegen where Clang
  needs to know what the ABI is (particularly through
  ASTContext::createCXXABI), and we should be able to override the
  target default if the flag is provided at that point.
- Expose the existing ABIs in TargetCXXABI as values that can be passed
  through this flag.
  - Create a .def file for these ABIs to make it easier to check flag
    values.
  - Add an error for diagnosing bad ABI flag values.

Differential Revision: https://reviews.llvm.org/D85802

1 files changed, 7 insertions, 12 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 93b49ec..aaf20ea 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -75,19 +75,14 @@ static llvm::cl::opt<bool> LimitedCoverage(
 static const char AnnotationSection[] = "llvm.metadata";
 
 static CGCXXABI *createCXXABI(CodeGenModule &CGM) {
-  switch (CGM.getTarget().getCXXABI().getKind()) {
-  case TargetCXXABI::Fuchsia:
-  case TargetCXXABI::GenericAArch64:
-  case TargetCXXABI::GenericARM:
-  case TargetCXXABI::iOS:
-  case TargetCXXABI::iOS64:
-  case TargetCXXABI::WatchOS:
-  case TargetCXXABI::GenericMIPS:
-  case TargetCXXABI::GenericItanium:
-  case TargetCXXABI::WebAssembly:
-  case TargetCXXABI::XL:
+  switch (CGM.getContext().getCXXABIKind()) {
+#define ITANIUM_CXXABI(Name, Str) case TargetCXXABI::Name:
+#define CXXABI(Name, Str)
+#include "clang/Basic/TargetCXXABI.def"
     return CreateItaniumCXXABI(CGM);
-  case TargetCXXABI::Microsoft:
+#define MICROSOFT_CXXABI(Name, Str) case TargetCXXABI::Name:
+#define CXXABI(Name, Str)
+#include "clang/Basic/TargetCXXABI.def"
     return CreateMicrosoftCXXABI(CGM);
   }