[clang][initlist] handle incomplete array type in Constant Expr Calculation (#155080)

fix: #151716

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/docs/ReleaseNotes.rst

@@ -338,6 +338,8 @@ Bug Fixes to C++ Support
 - Fix the parsing of variadic member functions when the ellipis immediately follows a default argument.(#GH153445)
 - Fixed a bug that caused ``this`` captured by value in a lambda with a dependent explicit object parameter to not be
   instantiated properly. (#GH154054)
+- Fixed a crash when implicit conversions from initialize list to arrays of
+  unknown bound during constant evaluation. (#GH151716)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/AST/ExprConstant.cpp

@@ -4030,10 +4030,12 @@ findSubobject(EvalInfo &Info, const Expr *E, const CompleteObject &Obj,
     LastField = nullptr;
     if (ObjType->isArrayType()) {
       // Next subobject is an array element.
-      const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(ObjType);
-      assert(CAT && "vla in literal type?");
+      const ArrayType *AT = Info.Ctx.getAsArrayType(ObjType);
+      assert((isa<ConstantArrayType>(AT) || isa<IncompleteArrayType>(AT)) &&
+             "vla in literal type?");
       uint64_t Index = Sub.Entries[I].getAsArrayIndex();
-      if (CAT->getSize().ule(Index)) {
+      if (const auto *CAT = dyn_cast<ConstantArrayType>(AT);
+          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)
@@ -4044,12 +4046,13 @@ 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 (const auto *CAT = dyn_cast<ConstantArrayType>(AT);
+            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