From 54c91ec440bfb00aa26fb8bd5372835e6863ea59 Mon Sep 17 00:00:00 2001
From: Andrea Mazzoleni <amadvance@gmail.com>
Date: Wed, 11 Nov 2015 08:02:54 +0100
Subject: [PATCH] Ensure a side effect in CRC computation

---
 cmdline/speed.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/cmdline/speed.c b/cmdline/speed.c
index e2dc6915..eb75d7ec 100644
--- a/cmdline/speed.c
+++ b/cmdline/speed.c
@@ -67,6 +67,14 @@ static int64_t diffgettimeofday(struct timeval *start, struct timeval *stop)
 	ds = size * (int64_t)count * nd; \
 	dt = diffgettimeofday(&start, &stop);
 
+/**
+ * Global variable used to propagate side effects.
+ *
+ * This is required to avoid optimizing compilers
+ * to remove code without side effects.
+ */
+static unsigned side_effect;
+
 void speed(int period)
 {
 	struct timeval start;
@@ -179,7 +187,7 @@ void speed(int period)
 
 	SPEED_START {
 		for (j = 0; j < nd; ++j)
-			crc32c_gen(0, v[j], size);
+			side_effect += crc32c_gen(0, v[j], size);
 	} SPEED_STOP
 
 	printf("%8" PRIu64, ds / dt);
@@ -192,7 +200,7 @@ void speed(int period)
 	if (raid_cpu_has_crc32()) {
 		SPEED_START {
 			for (j = 0; j < nd; ++j)
-				crc32c_x86(0, v[j], size);
+				side_effect += crc32c_x86(0, v[j], size);
 		} SPEED_STOP
 
 		printf("%8" PRIu64, ds / dt);