[clang][initlist] handle incomplete array type in Constant Expr Calculation

In #65918, support of incomplete array type is added in TryReferenceListInitialization.
It causes the crash in Constant Expr Calculation since it only considers the case where it is ConstantArrayType.

This patch wants to add support for incomplete array type also.

Author: HerrCai0907

clang/lib/AST/ExprConstant.cpp

@@ -4030,9 +4030,13 @@ findSubobject(EvalInfo &Info, const Expr *E, const CompleteObject &Obj,
     if (ObjType->isArrayType()) {
       // Next subobject is an array element.
       const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(ObjType);
-      assert(CAT && "vla in literal type?");
+      const IncompleteArrayType *IAT =
+          Info.Ctx.getAsIncompleteArrayType(ObjType);
+      const ArrayType *AT = CAT ? static_cast<const ArrayType *>(CAT)
+                                : static_cast<const ArrayType *>(IAT);
+      assert(AT && "vla in literal type?");
       uint64_t Index = Sub.Entries[I].getAsArrayIndex();
-      if (CAT->getSize().ule(Index)) {
+      if (CAT && CAT->getSize().ule(Index)) {
         // Note, it should not be possible to form a pointer with a valid
         // designator which points more than one past the end of the array.
         if (Info.getLangOpts().CPlusPlus11)
@@ -4043,12 +4047,12 @@ findSubobject(EvalInfo &Info, const Expr *E, const CompleteObject &Obj,
         return handler.failed();
       }
 
-      ObjType = CAT->getElementType();
+      ObjType = AT->getElementType();
 
       if (O->getArrayInitializedElts() > Index)
         O = &O->getArrayInitializedElt(Index);
       else if (!isRead(handler.AccessKind)) {
-        if (!CheckArraySize(Info, CAT, E->getExprLoc()))
+        if (CAT && !CheckArraySize(Info, CAT, E->getExprLoc()))
           return handler.failed();
 
         expandArray(*O, Index);

clang/test/CodeGenCXX/cxx20-p0388-unbound-ary.cpp

@@ -32,4 +32,19 @@ void foo(int a) {
   f({a});
 }
 
+constexpr int gh151716() {
+  int(&&g)[]{0,1,2};
+  return g[2];
+}
+// CHECK-LABEL: @_ZN3One10gh151716_fEv
+// CHECK-NEXT: entry:
+// CHECK-NEXT:   %v = alloca i32, align 4
+// CHECK-NEXT:   call void @llvm.lifetime.start.p0(ptr nonnull %v)
+// CHECK-NEXT:   store volatile i32 2, ptr %v, align 4
+// CHECK-NEXT:   call void @llvm.lifetime.end.p0(ptr nonnull %v)
+// CHECK-NEXT:   ret void
+void gh151716_f() {
+  volatile const int v = gh151716();
+}
+
 } // namespace One