[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, 18 insertions, 0 deletions

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index b2fa21e..4b0bd30 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -3512,6 +3512,10 @@ void CompilerInvocation::GenerateLangArgs(const LangOptions &Opts,
   if (Opts.getSignReturnAddressKey() ==
       LangOptions::SignReturnAddressKeyKind::BKey)
     GenerateArg(Args, OPT_msign_return_address_key_EQ, "b_key", SA);
+
+  if (Opts.CXXABI)
+    GenerateArg(Args, OPT_fcxx_abi_EQ, TargetCXXABI::getSpelling(*Opts.CXXABI),
+                SA);
 }
 
 bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
@@ -3996,6 +4000,20 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
     }
   }
 
+  // The value can be empty, which indicates the system default should be used.
+  StringRef CXXABI = Args.getLastArgValue(OPT_fcxx_abi_EQ);
+  if (!CXXABI.empty()) {
+    if (!TargetCXXABI::isABI(CXXABI)) {
+      Diags.Report(diag::err_invalid_cxx_abi) << CXXABI;
+    } else {
+      auto Kind = TargetCXXABI::getKind(CXXABI);
+      if (!TargetCXXABI::isSupportedCXXABI(T, Kind))
+        Diags.Report(diag::err_unsupported_cxx_abi) << CXXABI << T.str();
+      else
+        Opts.CXXABI = Kind;
+    }
+  }
+
   return Diags.getNumErrors() == NumErrorsBefore;
 }