P0145R3 (C++17 evaluation order tweaks): evaluate the right-hand side of

assignment and compound-assignment operators before the left-hand side. (Even
if it's an overloaded operator.)

This completes the implementation of P0145R3 + P0400R0 for all targets except
Windows, where the evaluation order guarantees for <<, >>, and ->* are
unimplementable as the ABI requires the function arguments are evaluated from
right to left (because parameter destructors are run from left to right in the
callee).

llvm-svn: 282556

1 files changed, 10 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index bca711fbc8c..63aa3467850 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -4121,8 +4121,17 @@ RValue CodeGenFunction::EmitCall(QualType CalleeType, llvm::Value *Callee,
   if (Chain)
     Args.add(RValue::get(Builder.CreateBitCast(Chain, CGM.VoidPtrTy)),
              CGM.getContext().VoidPtrTy);
+
+  // C++17 requires that we evaluate arguments to a call using assignment syntax
+  // right-to-left. It also requires that we evaluate arguments to operators
+  // <<, >>, and ->* left-to-right, but that is not possible under the MS ABI,
+  // so there is no corresponding "force left-to-right" case.
+  bool ForceRightToLeft = false;
+  if (auto *OCE = dyn_cast<CXXOperatorCallExpr>(E))
+    ForceRightToLeft = OCE->isAssignmentOp();
+
   EmitCallArgs(Args, dyn_cast<FunctionProtoType>(FnType), E->arguments(),
-               E->getDirectCallee(), /*ParamsToSkip*/ 0);
+               E->getDirectCallee(), /*ParamsToSkip*/ 0, ForceRightToLeft);
 
   const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeFreeFunctionCall(
       Args, FnType, /*isChainCall=*/Chain);