Subzero: Fixed deadlock with _start but no globals

tests_lit/asan_tests/no_globals.ll

Index: tests_lit/asan_tests/no_globals.ll
diff --git a/tests_lit/asan_tests/no_globals.ll b/tests_lit/asan_tests/no_globals.ll
new file mode 100644
index 0000000000000000000000000000000000000000..1a3d7f96f2ff43c09eac6facff74344d598feeb2
--- /dev/null
+++ b/tests_lit/asan_tests/no_globals.ll
@@ -0,0 +1,19 @@
+; Check that Subzero can instrument _start when there are no globals.
+; Previously Subzero would deadlock when _start was the first function. Also
+; test that instrumenting start does not deadlock waiting for nonexistent
+; global initializers to be lowered.
+
+; REQUIRES: no_minimal_build
+
+; RUN: %p2i -i %s --args -verbose=inst -fsanitize-address \
+; RUN:     | FileCheck --check-prefix=DUMP %s
+
+; RUN: %p2i -i %s --args -verbose=inst -fsanitize-address -threads=0 \
+; RUN:     | FileCheck --check-prefix=DUMP %s
+
+
+define void @_start(i32 %arg) {
+  ret void
+}
+
+; DUMP: __asan_init