Allow larger copies when not slow_unaligned_access and no padding.

Allow larger copies when not slow_unaligned_access and no padding.

This allows copy_blkmode_to_reg to perform larger copies when it is safe to do so by calculating
the bitsize per iteration doing the maximum copy allowed that does not read more
than the amount of bits left to copy.

Strictly speaking, this copying is only done if:

  1. the target supports fast unaligned access
  2. no padding is being used.

This should avoid the issues of the first patch (PR85123) but still work for targets that are safe
to do so.

Original patch https://gcc.gnu.org/ml/gcc-patches/2017-11/msg01088.html
Previous respin https://gcc.gnu.org/ml/gcc-patches/2018-04/msg00239.html

gcc/
2018-08-16  Tamar Christina  <tamar.christina@arm.com>

	* expr.c (copy_blkmode_to_reg): Perform larger copies when safe.

From-SVN: r263594