Simplify nvptx/slp* test-cases

Use signed loop iteration variable in nvtpx/slp* test-cases to work around
PR tree-optimizaion/81635.

2017-08-01  Tom de Vries  <tom@codesourcery.com>

	* gcc.target/nvptx/slp-2.c (foo): Use signed loop iteration variable.
	* gcc.target/nvptx/slp.c (foo): Same.

From-SVN: r250778

gcc/testsuite/ChangeLog

+2017-08-01  Tom de Vries  <tom@codesourcery.com>
+
+	* gcc.target/nvptx/slp-2.c (foo): Use signed loop iteration variable.
+	* gcc.target/nvptx/slp.c (foo): Same.
+
 2017-08-01  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/81181

gcc/testsuite/gcc.target/nvptx/slp-2.c

@@ -9,7 +9,7 @@ foo ()
 {
   long long int a, b;
 
-  unsigned int i;
+  int i;
   for (i = 0; i < 1000; i += 2)
     {
       a = p[i];

gcc/testsuite/gcc.target/nvptx/slp.c

@@ -9,7 +9,7 @@ foo ()
 {
   int a, b;
 
-  unsigned int i;
+  int i;
   for (i = 0; i < 1000; i += 2)
     {
       a = p[i];