[MS] Win64 va_arg should expect large arguments to be passed indirectly

Fixes PR20569

llvm-svn: 279774

1 files changed, 11 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 759e3d6f406..9fd7c493e03 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -3651,7 +3651,17 @@ void WinX86_64ABIInfo::computeInfo(CGFunctionInfo &FI) const {
 
 Address WinX86_64ABIInfo::EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
                                     QualType Ty) const {
-  return emitVoidPtrVAArg(CGF, VAListAddr, Ty, /*indirect*/ false,
+
+  bool IsIndirect = false;
+
+  // MS x64 ABI requirement: "Any argument that doesn't fit in 8 bytes, or is
+  // not 1, 2, 4, or 8 bytes, must be passed by reference."
+  if (isAggregateTypeForABI(Ty) || Ty->isMemberPointerType()) {
+    uint64_t Width = getContext().getTypeSize(Ty);
+    IsIndirect = Width > 64 || !llvm::isPowerOf2_64(Width);
+  }
+
+  return emitVoidPtrVAArg(CGF, VAListAddr, Ty, IsIndirect,
                           CGF.getContext().getTypeInfoInChars(Ty),
                           CharUnits::fromQuantity(8),
                           /*allowHigherAlign*/ false);