[Patch][expand] Check gimple statement to improve LSHIFT_EXP expand

[Patch][expand] Check gimple statement to improve LSHIFT_EXP expand

This patch improves LSHIFT_EXP expand if the shift operand comes from sign
extension and the shift result across word_mode_size boundary. See code
comments for details.

2015-08-19  Jiong.Wang  <jiong.wang@arm.com>

gcc/
  * expr.c (expand_expr_real_2): Check gimple statement during
  LSHIFT_EXPR expand.

gcc/testsuite
  * gcc.dg/wide_shift_64_1.c: New testcase.
  * gcc.dg/wide_shift_128_1.c: Likewise.
  * gcc.target/aarch64/ashlti3_1.c: Likewise.

From-SVN: r227018