Fix an assertion failure regression in isDesignatorAtObjectEnd for

__builtin_object_size with incomplete array type in struct

The commit r316245 introduced a regression that causes an assertion failure when
Clang tries to cast an IncompleteArrayType to a PointerType when evaluating
__builtin_object_size.

rdar://36094951

Differential Revision: https://reviews.llvm.org/D41405

llvm-svn: 321222

clang/lib/AST/ExprConstant.cpp

@@ -7420,7 +7420,10 @@ static bool isDesignatorAtObjectEnd(const ASTContext &Ctx, const LValue &LVal) {
     // If we don't know the array bound, conservatively assume we're looking at
     // the final array element.
     ++I;
-    BaseType = BaseType->castAs<PointerType>()->getPointeeType();
+    if (BaseType->isIncompleteArrayType())
+      BaseType = Ctx.getAsArrayType(BaseType)->getElementType();
+    else
+      BaseType = BaseType->castAs<PointerType>()->getPointeeType();
   }
 
   for (unsigned E = LVal.Designator.Entries.size(); I != E; ++I) {

clang/test/Sema/builtin-object-size.c

@@ -91,3 +91,22 @@ int pr31843() {
 
   return n;
 }
+
+typedef struct {
+  char string[512];
+} NestedArrayStruct;
+
+typedef struct {
+  int x;
+  NestedArrayStruct session[];
+} IncompleteArrayStruct;
+
+void rd36094951_IAS_builtin_object_size_assertion(IncompleteArrayStruct *p) {
+#define rd36094951_CHECK(mode)                                                 \
+  __builtin___strlcpy_chk(p->session[0].string, "ab", 2,                       \
+                          __builtin_object_size(p->session[0].string, mode))
+  rd36094951_CHECK(0);
+  rd36094951_CHECK(1);
+  rd36094951_CHECK(2);
+  rd36094951_CHECK(3);
+}