As Rainer reported at

  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67421

Also, as described at

  https://gcc.gnu.org/ml/gcc-patches/2015-08/msg01147.html

This patch relax the restriction on wide left shift. Previously we
always honor target private pattern, so when the following check be
true, we cancel the transformation.

  have_insn_for (ASHIFT, mode)

While it's better to do a cost on generated instruction sequences to
decided whether it's beneficial to honor backend pattern. Normally the
generic transformation will be better.

I haven't used GEN_FCN to invoke gen_* directly, instead I reused
"expand_variable_shift" to let it handle all the left work.

wide-shift-64 pass on sparc under the option "-mv8plus -mcpu=v9" now,
and arm32 also generate better code for wide-shift-64.

OK for trunk?

2015-09-03  Jiong. Wang  <jiong.wang@arm.com>

gcc/
  PR rtl-optimization/67421
  * expr.c (expand_expr_real_2): Cost instrcution sequences when doing
  left wide shift tranformation.

-- 
Regards,
Jiong