[ms-cxxabi] Use inalloca on win32 when passing non-trivial C++ objects

When a non-trivial parameter is present, clang now gathers up all the
parameters that lack inreg and puts them into a packed struct.  MSVC
always aligns each parameter to 4 bytes and no more, so this is a pretty
simple struct to lay out.

On win64, non-trivial records are passed indirectly.  Prior to this
change, clang was incorrectly using byval on win64.

I'm able to self-host a working clang with this change and additional
LLVM patches.

Reviewers: rsmith

Differential Revision: http://llvm-reviews.chandlerc.com/D2636

llvm-svn: 200597

1 files changed, 8 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 875591d0df9..3433c8ca30c 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -45,8 +45,14 @@ public:
   }
 
   RecordArgABI getRecordArgABI(const CXXRecordDecl *RD) const {
-    if (RD->hasNonTrivialCopyConstructor() || RD->hasNonTrivialDestructor())
-      return RAA_DirectInMemory;
+    if (RD->hasNonTrivialCopyConstructor() || RD->hasNonTrivialDestructor()) {
+      llvm::Triple::ArchType Arch = CGM.getTarget().getTriple().getArch();
+      if (Arch == llvm::Triple::x86)
+        return RAA_DirectInMemory;
+      // On x64, pass non-trivial records indirectly.
+      // FIXME: Test other Windows architectures.
+      return RAA_Indirect;
+    }
     return RAA_Default;
   }