[RELOAD] Don't assume subreg mem address is ok

This patch fixes a case where reload blindly assumes a subreg mem is
OK if its address has been partially reloaded by legitimize_reload_address.

	PR rtl-optimization/72771
	* reload.c (find_reloads): Don't assume that a subreg mem is OK
	when find_reloads_toplev returns address_reloaded==-1.
	(alternative_allows_const_pool_ref): Update comment.
testsuite/
	* gcc.c-torture/compile/pr72771.c: New.

From-SVN: r239549

gcc/ChangeLog

+2016-08-18  Alan Modra  <amodra@gmail.com>
+
+	PR rtl-optimization/72771
+	* reload.c (find_reloads): Don't assume that a subreg mem is OK
+	when find_reloads_toplev returns address_reloaded==-1.
+	(alternative_allows_const_pool_ref): Update comment.
+
 2015-08-17  Alan Hayward <alan.hayward@arm.com>
 
 	PR tree-optimization/71752

gcc/reload.c

@@ -3961,7 +3961,7 @@ find_reloads (rtx_insn *insn, int replace, int ind_levels, int live_known,
 	       there will be no reload needed at all.  */
 	    if (plus == NULL_RTX
 		&& subreg == NULL_RTX
-		&& alternative_allows_const_pool_ref (this_address_reloaded == 0
+		&& alternative_allows_const_pool_ref (this_address_reloaded != 1
 						      ? substed_operand[i]
 						      : NULL,
 						      recog_data.constraints[i],
@@ -4606,8 +4606,8 @@ find_reloads (rtx_insn *insn, int replace, int ind_levels, int live_known,
 
 /* Return true if alternative number ALTNUM in constraint-string
    CONSTRAINT is guaranteed to accept a reloaded constant-pool reference.
-   MEM gives the reference if it didn't need any reloads, otherwise it
-   is null.  */
+   MEM gives the reference if its address hasn't been fully reloaded,
+   otherwise it is NULL.  */
 
 static bool
 alternative_allows_const_pool_ref (rtx mem ATTRIBUTE_UNUSED,

gcc/testsuite/ChangeLog

+2016-08-18  Alan Modra  <amodra@gmail.com>
+
+	* gcc.c-torture/compile/pr72771.c: New.
+
 2016-08-17  Jakub Jelinek  <jakub@redhat.com>
 
 	PR fortran/67496

gcc/testsuite/gcc.c-torture/compile/pr72771.c

+void fn2(void);
+void fn3(unsigned long);
+
+signed char a;
+int b, c, e, f;
+float *d;
+
+void fn1(void) {
+        unsigned short g = 0;
+lbl_986:
+        for (;;) {
+                c = 0;
+                for (; c <= 2;) {
+                        *d = g;
+                        fn2();
+                        if (e)
+                                goto lbl_986;
+                }
+                g = 2;
+                for (; (short) g >= 0; g--) {
+                        for (; b;) {
+                                fn3(45360);
+                                f = 0;
+                                for (; a >= 0; a--)
+                                        ;
+                        }
+                }
+        }
+}