[26/77] Use is_a <scalar_int_mode> in subreg/extract simplifications

[26/77] Use is_a <scalar_int_mode> in subreg/extract simplifications

This patch adds is_a <scalar_int_mode> checks to various places that
were optimising subregs or extractions in ways that only made sense
for scalar integers.  Often the subreg transformations were looking
for extends, truncates or shifts and trying to remove the subreg, which
wouldn't be correct if the SUBREG_REG was a vector rather than a scalar.

The simplify_binary_operation_1 part also removes a redundant:

  GET_MODE (opleft) == GET_MODE (XEXP (opright, 0))

since this must be true for:

  (ior A (lshifrt B ...))  A == opleft, B == XEXP (opright, 0)

2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* combine.c (find_split_point): Add is_a <scalar_int_mode> checks.
	(make_compound_operation_int): Likewise.
	(change_zero_ext): Likewise.
	* expr.c (convert_move): Likewise.
	(convert_modes): Likewise.
	* fwprop.c (forward_propagate_subreg): Likewise.
	* loop-iv.c (get_biv_step_1): Likewise.
	* optabs.c (widen_operand): Likewise.
	* postreload.c (move2add_valid_value_p): Likewise.
	* recog.c (simplify_while_replacing): Likewise.
	* simplify-rtx.c (simplify_unary_operation_1): Likewise.
	(simplify_binary_operation_1): Likewise.  Remove redundant
	mode equality check.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@251478 138bc75d-0d04-0410-961f-82ee72b054a4