Add flag to request Clang is ABI-compatible with older versions of itself

This patch adds a flag -fclang-abi-compat that can be used to request that
Clang attempts to be ABI-compatible with some older version of itself.

This is provided on a best-effort basis; right now, this can be used to undo
the ABI change in r310401, reverting Clang to its prior C++ ABI for pass/return
by value of class types affected by that change, and to undo the ABI change in
r262688, reverting Clang to using integer registers rather than SSE registers
for passing <1 x long long> vectors. The intent is that we will maintain this
backwards compatibility path as we make ABI-breaking fixes in future.

The reversion to the old behavior for r310401 is also applied to the PS4 target
since that change is not part of its platform ABI (which is essentially to do
whatever Clang 3.2 did).

llvm-svn: 311823

1 files changed, 2 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/ABIInfo.h b/clang/lib/CodeGen/ABIInfo.h
index e4dce2f2a00..575506da84d 100644
--- a/clang/lib/CodeGen/ABIInfo.h
+++ b/clang/lib/CodeGen/ABIInfo.h
@@ -24,6 +24,7 @@ namespace llvm {
 
 namespace clang {
   class ASTContext;
+  class CodeGenOptions;
   class TargetInfo;
 
 namespace CodeGen {
@@ -68,6 +69,7 @@ namespace swiftcall {
     llvm::LLVMContext &getVMContext() const;
     const llvm::DataLayout &getDataLayout() const;
     const TargetInfo &getTarget() const;
+    const CodeGenOptions &getCodeGenOpts() const;
 
     /// Return the calling convention to use for system runtime
     /// functions.