[Bug target/57329] ICE with -O2 and -mthumb

["terry.guo at arm dot com" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57329

Terry Guo <terry.guo at arm dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |terry.guo at arm dot com

--- Comment #2 from Terry Guo <terry.guo at arm dot com> ---
The case has operations on vector for Thumb-1 targets. Thus subreg is generated
for example:

(insn 65 64 66 2 (set (subreg:SI (reg:TI 137 [ D.4126 ]) 4)
        (reg:SI 211)) 187 {*thumb1_movsi_insn}
     (nil))

The subreg:SI is supposed to be turned into normal reg:SI in subreg1 pass.
However current 4.8 branch incorrectly calculates the rtx cost of such
transformation.

Speed costs
===========
SI move: from zero cost 4, from reg cost 4
DI move: original cost 4, split cost 4 * 2
TI move: original cost 4, split cost 4 * 4
EI move: original cost 4, split cost 4 * 6

The subreg will be kept until IRA stage and causes ICE there.

With Bin's patch at http://gcc.gnu.org/ml/gcc-cvs/2013-03/msg00784.html, we
will get correct rtx cost:

Speed costs
===========
SI move: from zero cost 4, from reg cost 4
DI move: original cost 8, split cost 4 * 2
TI move: original cost 16, split cost 4 * 4
EI move: original cost 24, split cost 4 * 6

Then the split happens, we will get:

(insn 65 64 66 2 (set (reg:SI 393 [ D.4126+4 ])
        (reg:SI 211)) 187 {*thumb1_movsi_insn}
     (nil))

and then everything works well.

I believe this is the cause of the issue and am doing back port to 4.8 branch.