clang-cl: Evaluate arguments left-to-right in constructor call with initializer list (PR31831)

[hans]

Summary

clang-cl would evaluate the arguments right-to-left (see PR), and for non-Windows targets I suppose we only got it because we were already emitting left-to-right in CodeGenFunction::EmitCallArgs.

[rnk]

lgtm

Can you check if we got this wrong in clang 3.8 and 3.9? I'm wondering if this was a regression, or if we always got this wrong.

[hans]

In D29350#662525, @rnk wrote:

Can you check if we got this wrong in clang 3.8 and 3.9? I'm wondering if this was a regression, or if we always got this wrong.

I tried back to 3.5, and it seems we just always got it wrong.

lib/CodeGen/CGClass.cpp

if (isMemcpyEquivalentSpecialMember(D)) {
     Address Src = EmitLValue(Arg).getAddress();
     QualType DestTy = getContext().getTypeDeclType(D->getParent());
     EmitAggregateCopyCtor(This, Src, DestTy, SrcTy);
     return;
   }
 
   // Add the rest of the user-supplied arguments.
   const FunctionProtoType *FPT = D->getType()->castAs<FunctionProtoType>();
-  EmitCallArgs(Args, FPT, E->arguments(), E->getConstructor());
+  EvaluationOrder Order = E->isListInitialization()
+                              ? EvaluationOrder::ForceLeftToRight
+                              : EvaluationOrder::Default;
+  EmitCallArgs(Args, FPT, E->arguments(), E->getConstructor(),
+               /*ParamsToSkip*/ 0, Order);
 
   EmitCXXConstructorCall(D, Type, ForVirtualBase, Delegating, This, Args);
 }
 
 static bool canEmitDelegateCallArgs(CodeGenFunction &CGF,
                                     const CXXConstructorDecl *Ctor,
                                     CXXCtorType Type, CallArgList &Args) {
   // We can't forward a variadic call.

test/CodeGenCXX/initializer-list-ctor-order.cpp

+// RUN: %clang_cc1 -std=c++11 %s -emit-llvm -o - -triple %itanium_abi_triple | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-ITANIUM
+// RUN: %clang_cc1 -std=c++11 %s -emit-llvm -o - -triple i686-windows        | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-MS
+
+extern "C" {
+int f();
+int g();
+}
+
+struct A {
+  A(int, int);
+};
+
+
+void foo() {
+  A a{f(), g()};
+}
+// CHECK-ITANIUM-LABEL: define void @_Z3foov
+// CHECK-MS-LABEL: define void @"\01?foo@@YAXXZ"
+// CHECK: call i32 @f()
+// CHECK: call i32 @g()
+
+struct B : A {
+  B();
+};
+B::B() : A{f(), g()} {}
+// CHECK-ITANIUM-LABEL: define void @_ZN1BC2Ev
+// CHECK-MS-LABEL: define x86_thiscallcc %struct.B* @"\01??0B@@QAE@XZ"
+// CHECK: call i32 @f()
+// CHECK: call i32 @g()