Make more use of benchmark::DoNotOptimize in benchmarks.

A lot of these benchmarks predate DoNotOptimize and rolled their own
hacks.

Bug: http://b/148307629
Test: ran benchmarks before & after and got similar results
Change-Id: If44699d261b687f6253af709edda58f4c90fb285

1 files changed, 1 insertions, 2 deletions

diff --git a/benchmarks/stdio_benchmark.cpp b/benchmarks/stdio_benchmark.cpp
index 037bbd911..03f3f2903 100644
--- a/benchmarks/stdio_benchmark.cpp
+++ b/benchmarks/stdio_benchmark.cpp
@@ -155,9 +155,8 @@ static void FopenFgetcFclose(benchmark::State& state, bool no_locking) {
   while (state.KeepRunning()) {
     FILE* fp = fopen("/dev/zero", "re");
     if (no_locking) __fsetlocking(fp, FSETLOCKING_BYCALLER);
-    volatile int c __attribute__((unused));
     for (size_t i = 0; i < nbytes; ++i) {
-      c = fgetc(fp);
+      benchmark::DoNotOptimize(fgetc(fp));
     }
     fclose(fp);
   }