Switch to a different workaround for unimplementability of P0145R3 in MS ABIs.

Instead of ignoring the evaluation order rule, ignore the "destroy parameters
in reverse construction order" rule for the small number of problematic cases.
This only causes incorrect behavior in the rare case where both parameters to
an overloaded operator <<, >>, ->*, &&, ||, or comma are of class type with
non-trivial destructor, and the program is depending on those parameters being
destroyed in reverse construction order.

We could do a little better here by reversing the order of parameter
destruction for those functions (and reversing the argument evaluation order
for all direct calls, not just those with operator syntax), but that is not a
complete solution to the problem, as the same situation can be reached by an
indirect function call.

Approach reviewed off-line by rnk.

llvm-svn: 282777

1 files changed, 12 insertions, 4 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 378a2562f8a..db579854886 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -3318,13 +3318,22 @@ public:
   static bool isObjCMethodWithTypeParams(const T *) { return false; }
 #endif
 
+  enum class EvaluationOrder {
+    ///! No language constraints on evaluation order.
+    Default,
+    ///! Language semantics require left-to-right evaluation.
+    ForceLeftToRight,
+    ///! Language semantics require right-to-left evaluation.
+    ForceRightToLeft
+  };
+
   /// EmitCallArgs - Emit call arguments for a function.
   template <typename T>
   void EmitCallArgs(CallArgList &Args, const T *CallArgTypeInfo,
                     llvm::iterator_range<CallExpr::const_arg_iterator> ArgRange,
                     const FunctionDecl *CalleeDecl = nullptr,
                     unsigned ParamsToSkip = 0,
-                    bool ForceRightToLeftEvaluation = false) {
+                    EvaluationOrder Order = EvaluationOrder::Default) {
     SmallVector<QualType, 16> ArgTypes;
     CallExpr::const_arg_iterator Arg = ArgRange.begin();
 
@@ -3364,15 +3373,14 @@ public:
     for (auto *A : llvm::make_range(Arg, ArgRange.end()))
       ArgTypes.push_back(getVarArgType(A));
 
-    EmitCallArgs(Args, ArgTypes, ArgRange, CalleeDecl, ParamsToSkip,
-                 ForceRightToLeftEvaluation);
+    EmitCallArgs(Args, ArgTypes, ArgRange, CalleeDecl, ParamsToSkip, Order);
   }
 
   void EmitCallArgs(CallArgList &Args, ArrayRef<QualType> ArgTypes,
                     llvm::iterator_range<CallExpr::const_arg_iterator> ArgRange,
                     const FunctionDecl *CalleeDecl = nullptr,
                     unsigned ParamsToSkip = 0,
-                    bool ForceRightToLeftEvaluation = false);
+                    EvaluationOrder Order = EvaluationOrder::Default);
 
   /// EmitPointerWithAlignment - Given an expression with a pointer
   /// type, emit the value and compute our best estimate of the