Remove DImode expansions for 1-bit shifts

Remove DImode expansions for 1-bit shifts

A left shift of 1 can always be done using an add, so slightly adjust rtx
cost for DImode left shift by 1 so that adddi3 is preferred in all cases,
and the arm_ashldi3_1bit is redundant.

DImode right shifts of 1 are rarely used (6 in total in the GCC binary),
so there is little benefit of the arm_ashrdi3_1bit and arm_lshrdi3_1bit
patterns.  The generated code is better and faster without these shifts
as it allows early expansion, optimization and better register allocation.

    gcc/
	* config/arm/arm.md (ashldi3): Remove shift by 1 expansion.
	(arm_ashldi3_1bit): Remove pattern.
	(ashrdi3): Remove shift by 1 expansion.
	(arm_ashrdi3_1bit): Remove pattern.
	(lshrdi3): Remove shift by 1 expansion.
	(arm_lshrdi3_1bit): Remove pattern.
	* config/arm/arm.c (arm_rtx_costs_internal): Slightly increase
	cost of ashldi3 by 1.
	* config/arm/neon.md (ashldi3_neon): Remove shift by 1 expansion.
	(<shift>di3_neon): Likewise.

From-SVN: r254237