Teach ARM va_arg to ignore empty structs.

Empty structs are ignored for parameter passing purposes, but va_arg was
incrementing the pointer anyway which could lead to va_list getting out of
sync.

llvm-svn: 184605

1 files changed, 27 insertions, 0 deletions

diff --git a/clang/test/CodeGenCXX/arm-vaarg.cpp b/clang/test/CodeGenCXX/arm-vaarg.cpp
new file mode 100644
index 00000000000..9850fb342fa
--- /dev/null
+++ b/clang/test/CodeGenCXX/arm-vaarg.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -triple armv7-apple-ios -emit-llvm -o - %s | FileCheck %s
+struct Empty {};
+
+Empty emptyvar;
+
+int take_args(int a, ...) {
+  __builtin_va_list l;
+  __builtin_va_start(l, a);
+// CHECK: call void @llvm.va_start
+
+  emptyvar = __builtin_va_arg(l, Empty);
+// CHECK: load i8**
+// CHECK-NOT: getelementptr
+// CHECK: [[EMPTY_PTR:%[a-zA-Z0-9._]+]] = bitcast i8* {{%[a-zA-Z0-9._]+}} to %struct.Empty*
+
+  // It's conceivable that EMPTY_PTR may not actually be a valid pointer
+  // (e.g. it's at the very bottom of the stack and the next page is
+  // invalid). This doesn't matter provided it's never loaded (there's no
+  // well-defined way to tell), but it becomes a problem if we do try to use it.
+// CHECK-NOT: load %struct.Empty* [[EMPTY_PTR]]
+
+  int i = __builtin_va_arg(l, int);
+// CHECK: load i32*
+
+  __builtin_va_end(l);
+  return i;
+}