Fix PR46932: Block auto increment on frame pointer

Block auto increment on frame pointer references.  This is never
beneficial since the SFP expands into SP+C or FP+C during register
allocation.  The generated code for the testcase is now as expected:

	str	x30, [sp, -32]!
	strb	w0, [sp, 31]
	add	x0, sp, 31
	bl	foo3
	ldr	x30, [sp], 32
	ret

    gcc/
	PR middle-end/46932
	* auto-inc-dec.c (parse_add_or_inc): Block autoinc on sfp.

    gcc/testsuite/
	PR middle-end/46932
	* gcc.dg/pr46932.c: New testcase.

From-SVN: r250564

gcc/ChangeLog

+2017-07-26  Wilco Dijkstra  <wdijkstr@arm.com>
+
+	PR middle-end/46932
+	* auto-inc-dec.c (parse_add_or_inc): Block autoinc on sfp.
+
 2017-07-26  Martin Liska  <mliska@suse.cz>
 
 	PR sanitize/81186

gcc/auto-inc-dec.c

@@ -769,6 +769,12 @@ parse_add_or_inc (rtx_insn *insn, bool before_mem)
   inc_insn.pat = pat;
   inc_insn.reg_res = SET_DEST (pat);
   inc_insn.reg0 = XEXP (SET_SRC (pat), 0);
+
+  /* Block any auto increment of the frame pointer since it expands into
+     an addition and cannot be removed by copy propagation.  */
+  if (inc_insn.reg0 == frame_pointer_rtx)
+    return false;
+
   if (rtx_equal_p (inc_insn.reg_res, inc_insn.reg0))
     inc_insn.form = before_mem ? FORM_PRE_INC : FORM_POST_INC;
   else

gcc/testsuite/ChangeLog

+2017-07-26  Wilco Dijkstra  <wdijkstr@arm.com>
+
+	PR middle-end/46932
+	* gcc.dg/pr46932.c: New testcase.
+
 2017-07-26  Martin Liska  <mliska@suse.cz>
 
 	PR sanitize/81186

gcc/testsuite/gcc.dg/pr46932.c

+/* { dg-options "-O2 -fdump-rtl-auto_inc_dec" } */
+
+/* Check that accesses based on the frame pointer do not
+   use auto increment.  */
+
+extern void foo(char*);
+void t01(char t)
+{
+  char c = t;
+  foo(&c);
+}
+
+/* { dg-final { scan-rtl-dump-not "success" "auto_inc_dec" } } */