lmbench: avoid gcc optimize-away multiplication

Change expression used in do_integer_mul and do_uint64_mul
benchmarks so GCC doesn't optimize-away the loops,

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Armin Kuster <akuster808@gmail.com>

2 files changed, 80 insertions, 0 deletions

diff --git a/meta-oe/recipes-benchmark/lmbench/lmbench/0001-avoid-gcc-optimize-away-the-loops.patch b/meta-oe/recipes-benchmark/lmbench/lmbench/0001-avoid-gcc-optimize-away-the-loops.patch
new file mode 100644
index 000000000..2d8a2468a
--- /dev/null
+++ b/meta-oe/recipes-benchmark/lmbench/lmbench/0001-avoid-gcc-optimize-away-the-loops.patch
@@ -0,0 +1,79 @@
+[PATCH] avoid gcc optimize-away the loops
+
+Upstream-Status: pending
+
+Change expression used in do_integer_mul and do_uint64_mul
+benchmarks so GCC doesn't optimize-away the loops, other
+things are same:
+-               TEN(r *= s;); r -= t;
++               i = 0;
++               while ( i++ < 10)
++                       r *= s;
++               r -= t;
+
+and TEN is macro:
+        #define TEN(a) a a a a a a a a a a
+
+Signed-off-by: Roy Li <rongqing.li@windriver.com>
+---
+ src/lat_ops.c | 30 +++++++++++++++++++++++++-----
+ 1 file changed, 25 insertions(+), 5 deletions(-)
+
+diff --git a/src/lat_ops.c b/src/lat_ops.c
+index d343ff3..457072b 100644
+--- a/src/lat_ops.c
++++ b/src/lat_ops.c
+@@ -126,11 +126,23 @@ do_integer_mul(iter_t iterations, void* cookie)
+        struct _state *pState = (struct _state*)cookie;
+        register int r = pState->N + 37431;
+        register int s = pState->N + 4;
+-       register int t = r * s * s * s * s * s * s * s * s * s * s - r;
++       register int t = r;
++       int i = 0;
++
++       while ( i++ < 10)
++               t *= s;
++       t -= r;
+ 
+        while (iterations-- > 0) {
+-               TEN(r *= s;); r -= t;
+-               TEN(r *= s;); r -= t;
++               i = 0;
++               while ( i++ < 10)
++                       r *= s;
++               r -= t;
++
++               i = 0;
++               while ( i++ < 10)
++                       r *= s;
++               r -= t;
+        }
+        use_int(r);
+ }
+@@ -207,13 +219,21 @@ do_int64_mul(iter_t iterations, void* cookie)
+        register int64 r = (int64)pState->N + 37420;
+        register int64 s = (int64)pState->N + 4;
+        register int64 t;
++       int i = 0;
+ 
+        r += (int64)(pState->N + 6)<<32;
+        t = r * s * s * s * s * s * s * s * s * s * s - r;
+ 
+        while (iterations-- > 0) {
+-               TEN(r *= s;); r -= t;
+-               TEN(r *= s;); r -= t;
++               i = 0;
++               while ( i++ < 10)
++                       r *= s;
++               r -= t;
++
++               i = 0;
++               while ( i++ < 10)
++                       r *= s;
++               r -= t;
+        }
+        use_int((int)r);
+ }
+-- 
+2.8.1
+
diff --git a/meta-oe/recipes-benchmark/lmbench/lmbench_3.0-a9.bb b/meta-oe/recipes-benchmark/lmbench/lmbench_3.0-a9.bb
index 5459bf9cb..a62389d09 100644
--- a/meta-oe/recipes-benchmark/lmbench/lmbench_3.0-a9.bb
+++ b/meta-oe/recipes-benchmark/lmbench/lmbench_3.0-a9.bb
@@ -18,6 +18,7 @@ SRC_URI = "${SOURCEFORGE_MIRROR}/lmbench/lmbench-${PV}.tgz \
            file://use-base_libdir-instead-of-hardcoded-lib.patch \
            file://lmbench_result_html_report.patch \
            file://fix-lmbench-memory-check-failure.patch \
+           file://0001-avoid-gcc-optimize-away-the-loops.patch \
 "
 SRC_URI[md5sum] = "b3351a3294db66a72e2864a199d37cbf"
 SRC_URI[sha256sum] = "cbd5777d15f44eab7666dcac418054c3c09df99826961a397d9acf43d8a2a551"