testcase for last_vuse in FRE

This adds a testcase for some basic FRE functionality.

2020-02-25  Richard Biener  <rguenther@suse.de>

	* gcc.dg/tree-ssa/ssa-fre-86.c: New testcase.

gcc/testsuite/ChangeLog

 2020-02-25  Richard Biener  <rguenther@suse.de>
 
+	* gcc.dg/tree-ssa/ssa-fre-86.c: New testcase.
+
+2020-02-25  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/93868
 	* gcc.dg/torture/pr93868.c: New testcase.
 

gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-86.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-fre1" } */
+
+int foo(int *p, int b, float *q)
+{
+  int tem;
+  if (b)
+    {
+      *q = 0;
+      tem = *p;
+    }
+  else
+    {
+      *q = 1;
+      tem = *p;
+    }
+  return *p - tem;
+}
+
+/* { dg-final { scan-tree-dump "return 0;" "fre1" } } */