[PATCH][gcse] Use emit_move_insn rather than creating SET rtx and emitting that

[Kyrill Tkachov <kyrylo dot tkachov at arm dot com>]

Hi all,

This patches fixes the ICE reported at 
https://gcc.gnu.org/ml/gcc-patches/2015-03/msg00949.html
The problem is that gcse generates a (set (reg:OI) (const_int 0)) that 
doesn't match anything
in the arm backend. That SET was created through processing an insn 
generated by the neon_movoi
insn in neon.md. gcse created an OImode reg, put it in a SET rtx with 
const_int 0 and tried to
recognise it which failed.

As pointed out by James Greenhalgh offline the correct thing would have 
been to do an
emit_move_insn to let the backend expanders do the right thing 
(especially in the concerned
testcase gcc.c-torture/execute/pr65427.c that uses 256-bit vectors that 
arm doesn't support
natively).

Bootstrapped and tested on arm, x86, aarch64.
This ICE doesn't happen with 4.9 and 4.8 so it's only a regression for 
GCC 5.
The currently ICE'ins testcase passes now, so no new testcase is added.

Ok for trunk?

Thanks,
Kyrill

2015-03-18  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
            James Greenhalgh  <james.greenhalgh@arm.com>

    * gcse.c (process_insert_insn): Use emit_move_insn rather than
    generating a SET rtx and emitting it.

commit 9b6366d27deb2a366c7cfd308e02ab158527f430
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date:   Wed Mar 18 16:05:36 2015 +0000

    [gcse] Use emit_move_insn rather than creating SET rtx and emitting that

diff --git a/gcc/gcse.c b/gcc/gcse.c
index e03b36c..cc55e91 100644
--- a/gcc/gcse.c
+++ b/gcc/gcse.c
@@ -2168,7 +2168,7 @@ process_insert_insn (struct gcse_expr *expr)
      insn will be recognized (this also adds any needed CLOBBERs).  */
   else
     {
-      rtx_insn *insn = emit_insn (gen_rtx_SET (VOIDmode, reg, exp));
+      rtx_insn *insn = emit_move_insn (reg, exp);
 
       if (insn_invalid_p (insn, false))
 	gcc_unreachable ();