[BZ #15424] Prevent optimizing out of benchmark function call

[Siddhesh Poyarekar <siddhesh at redhat dot com>]

Hi,

The compiler would optimize the benchmark function call out of the
loop and call it only once, resulting in blazingly fast times for some
benchmarks (notably atan, sin and cos).  This patch marks the inputs
as volatile so that the code is forced to read again from the input
for each iteration.  The modf code doesn't need the change right now,
but I've added it in any for consistency and to prevent the
possibility of a future compiler finding an optimization opportunity
there.

OK to commit?

Siddhesh

	[BZ #15424]
	* benchtests/bench-modf.c (struct args): Mark arg0 as
	volatile.
	* scripts/bench.pl: Mark members of struct args as volatile.

diff --git a/benchtests/bench-modf.c b/benchtests/bench-modf.c
index 7fae7dc..2b50665 100644
--- a/benchtests/bench-modf.c
+++ b/benchtests/bench-modf.c
@@ -21,7 +21,7 @@ extern double modf (double, double *);
 
 struct args
 {
-  double arg0;
+  volatile double arg0;
 } in[] =
 {
   {  42.42 },
diff --git a/scripts/bench.pl b/scripts/bench.pl
index dcc5ead..dcf1355 100755
--- a/scripts/bench.pl
+++ b/scripts/bench.pl
@@ -71,7 +71,7 @@ else {
       $decl = "$decl,";
     }
 
-    $arg_struct = "$arg_struct $arg arg$num;";
+    $arg_struct = "$arg_struct volatile $arg arg$num;";
     $bench_func = "$bench_func variants[v].in[i].arg$num";
     $decl = "$decl $arg";
     $num = $num + 1;