Make more use of subreg_lowpart_offset

[Jeff Law]

On 08/23/2017 04:51 AM, Richard Sandiford wrote:
> This patch uses subreg_lowpart_offset in places that open-coded
> the calculation.  It also uses it in regcprop.c to test whether,
> after a mode change, the first register in a multi-register group
> is still the right one.
> 
> Tested on aarch64-linux-gnu and x86_64-linux-gnu, and by making sure
> that there were no differences in testsuite assembly output for one
> target per CPU.  OK to install?
> 
> Richard
> 
> 
> 2017-08-23  Richard Sandiford  <richard.sandiford@linaro.org>
> 	    Alan Hayward  <alan.hayward@arm.com>
> 	    David Sherwood  <david.sherwood@arm.com>
> 
> gcc/
> 	* calls.c (expand_call): Use subreg_lowpart_offset.
> 	* cse.c (cse_insn): Likewise.
> 	* regcprop.c (copy_value): Likewise.
> 	(copyprop_hardreg_forward_1): Likewise.
It was far from obvious that the open coded versions actually
corresponded to subreg_lowpart_offset.  Sorry it took so long.

OK.
jeff