Prevent infinite loops from being optimized away.

llvm/llvm-project@6c31295 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: 374546142

test/syscalls/linux/BUILD

@@ -1,4 +1,4 @@
-load("//tools:defs.bzl", "cc_binary", "cc_library", "default_net_util", "gtest", "select_arch", "select_system")
+load("//tools:defs.bzl", "cc_binary", "cc_library", "default_net_util", "gbenchmark", "gtest", "select_arch", "select_system")
 
 package(
     default_visibility = ["//:sandbox"],
@@ -3785,17 +3785,18 @@ cc_binary(
     srcs = ["timers.cc"],
     linkstatic = 1,
     deps = [
-        "//test/util:cleanup",
-        "@com_google_absl//absl/flags:flag",
-        "@com_google_absl//absl/time",
+        gbenchmark,
         gtest,
+        "//test/util:cleanup",
         "//test/util:logging",
         "//test/util:multiprocess_util",
         "//test/util:posix_error",
         "//test/util:signal_util",
         "//test/util:test_util",
         "//test/util:thread_util",
         "//test/util:timer_util",
+        "@com_google_absl//absl/flags:flag",
+        "@com_google_absl//absl/time",
     ],
 )
 

test/syscalls/linux/timers.cc

@@ -26,6 +26,7 @@
 #include "absl/flags/flag.h"
 #include "absl/time/clock.h"
 #include "absl/time/time.h"
+#include "benchmark/benchmark.h"
 #include "test/util/cleanup.h"
 #include "test/util/logging.h"
 #include "test/util/multiprocess_util.h"
@@ -92,6 +93,8 @@ TEST(TimerTest, ProcessKilledOnCPUSoftLimit) {
     TEST_PCHECK(setrlimit(RLIMIT_CPU, &cpu_limits) == 0);
     MaybeSave();
     for (;;) {
+      int x = 0;
+      benchmark::DoNotOptimize(x);  // Don't optimize this loop away.
     }
   }
   ASSERT_THAT(pid, SyscallSucceeds());
@@ -151,6 +154,8 @@ TEST(TimerTest, ProcessPingedRepeatedlyAfterCPUSoftLimit) {
     TEST_PCHECK(setrlimit(RLIMIT_CPU, &cpu_limits) == 0);
     MaybeSave();
     for (;;) {
+      int x = 0;
+      benchmark::DoNotOptimize(x);  // Don't optimize this loop away.
     }
   }
   ASSERT_THAT(pid, SyscallSucceeds());
@@ -197,6 +202,8 @@ TEST(TimerTest, ProcessKilledOnCPUHardLimit) {
     TEST_PCHECK(setrlimit(RLIMIT_CPU, &cpu_limits) == 0);
     MaybeSave();
     for (;;) {
+      int x = 0;
+      benchmark::DoNotOptimize(x);  // Don't optimize this loop away.
     }
   }
   ASSERT_THAT(pid, SyscallSucceeds());