[PATCH] PR67305, tighten neon_vector_mem_operand on eliminable registers

[Jiong Wang <jiong dot wang at foss dot arm dot com>]

As discussed at the bugzilla

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67305

neon_vector_mem_operand is broken.  As the comments says
"/* Reject eliminable registers.  */", the code block at the head
of this function which checks eliminable registers is designed to do
early reject only, there shouldn't be any early accept.

If this code hunk doesn't reject the incoming rtx, then the rtx pattern
should still go through all default checks below. All other similar
functions, thumb1_legitimate_address_p, arm_coproc_mem_operand,
neon_struct_mem_operand etc are exactly follow this check flow.

So as Jim Wilson commented on the bugzilla, instead of "return !strict",
we need to only do the check if strict be true, and only does rejection
which means return FALSE, for all other cases, we need to go through
those normal checks below.

neon_vector_mem_operand is only used by several misalign pattern, I
guess that's why this bug is not exposed for long time.

boostrap & regression OK on armv8 aarch32, ok for trunk?

2015-11-04  Jiong Wang  <jiong.wang@arm.com>
            Jim Wilson  <wilson@gcc.gnu.org>

gcc/
  PR target/67305
  * config/arm/arm.md (neon_vector_mem_operand): Return FALSE if strict
  be true and eliminable registers mentioned.

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 87e55e9..7fbf897 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -12957,14 +12957,14 @@ neon_vector_mem_operand (rtx op, int type, bool strict)
   rtx ind;
 
   /* Reject eliminable registers.  */
-  if (! (reload_in_progress || reload_completed)
-      && (   reg_mentioned_p (frame_pointer_rtx, op)
+  if (strict && ! (reload_in_progress || reload_completed)
+      && (reg_mentioned_p (frame_pointer_rtx, op)
 	  || reg_mentioned_p (arg_pointer_rtx, op)
 	  || reg_mentioned_p (virtual_incoming_args_rtx, op)
 	  || reg_mentioned_p (virtual_outgoing_args_rtx, op)
 	  || reg_mentioned_p (virtual_stack_dynamic_rtx, op)
 	  || reg_mentioned_p (virtual_stack_vars_rtx, op)))
-    return !strict;
+    return FALSE;
 
   /* Constants are converted into offsets from labels.  */
   if (!MEM_P (op))