tree-optimization/97089 - fix bogus unsigned division replacement

This fixes bogus replacing of an unsigned (-x)/y division by
-(x/y).

2020-09-18  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/97089
	* tree-ssa-sccvn.c (visit_nary_op): Do not replace unsigned
	divisions.

gcc/tree-ssa-sccvn.c

@@ -4824,8 +4824,11 @@ visit_nary_op (tree lhs, gassign *stmt)
 	    }
 	}
       break;
-    case RDIV_EXPR:
     case TRUNC_DIV_EXPR:
+      if (TYPE_UNSIGNED (type))
+	break;
+      /* Fallthru.  */
+    case RDIV_EXPR:
     case MULT_EXPR:
       /* Match up ([-]a){/,*}([-])b with v=a{/,*}b, replacing it with -v.  */
       if (! HONOR_SIGN_DEPENDENT_ROUNDING (type))