Prevent infinite loops from being optimized away.

https://github.com/llvm/llvm-project/commit/6c3129549374c0e81e28fd0a21e96f8087b63a78
adds "mustprogress" to loops, which causes empty, side-effect free loops to be
optimized away. These loops are intentionally infinite for purposes of testing,
so add asm statements that prevent them from being removed.

PiperOrigin-RevId: 375188453

test/syscalls/linux/BUILD

@@ -520,13 +520,14 @@ cc_binary(
     srcs = ["concurrency.cc"],
     linkstatic = 1,
     deps = [
-        "@com_google_absl//absl/strings",
-        "@com_google_absl//absl/time",
+        gbenchmark,
         gtest,
         "//test/util:platform_util",
         "//test/util:test_main",
         "//test/util:test_util",
         "//test/util:thread_util",
+        "@com_google_absl//absl/strings",
+        "@com_google_absl//absl/time",
     ],
 )
 

test/syscalls/linux/concurrency.cc

@@ -20,6 +20,7 @@
 #include "absl/strings/string_view.h"
 #include "absl/time/clock.h"
 #include "absl/time/time.h"
+#include "benchmark/benchmark.h"
 #include "test/util/platform_util.h"
 #include "test/util/test_util.h"
 #include "test/util/thread_util.h"
@@ -106,6 +107,8 @@ TEST(ConcurrencyTest, MultiProcessConcurrency) {
   pid_t child_pid = fork();
   if (child_pid == 0) {
     while (true) {
+      int x = 0;
+      benchmark::DoNotOptimize(x);  // Don't optimize this loop away.
     }
   }
   ASSERT_THAT(child_pid, SyscallSucceeds());