[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, 1 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index cb0523898c3a..ab133b513733 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -75,7 +75,7 @@ static llvm::cl::opt<bool> LimitedCoverage(
 static const char AnnotationSection[] = "llvm.metadata";
 
 static CGCXXABI *createCXXABI(CodeGenModule &CGM) {
-  switch (CGM.getTarget().getCXXABI().getKind()) {
+  switch (CGM.getContext().getCXXABIKind()) {
   case TargetCXXABI::AppleARM64:
   case TargetCXXABI::Fuchsia:
   case TargetCXXABI::GenericAArch64: