Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -9509,6 +9509,8 @@
 
     // Figure out how many T's we're copying.
     uint64_t TSize = Info.Ctx.getTypeSizeInChars(T).getQuantity();
+    if (TSize == 0)
+      return false;
     if (!WChar) {
       uint64_t Remainder;
       llvm::APInt OrigN = N;
Index: clang/test/Sema/builtin-memcpy.c
===================================================================
--- /dev/null
+++ clang/test/Sema/builtin-memcpy.c
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 %s -fsyntax-only -verify
+
+/// Zero-sized structs should not crash.
+int b() {
+  struct {      } a[10];
+  __builtin_memcpy(&a[2], a, 2); // expected-warning {{buffer has size 0, but size argument is 2}}
+  return 0;
+}