re PR target/592 ([ARM/Thumb] Poor choice of PIC register)

re PR target/592 ([ARM/Thumb] Poor choice of PIC register)

	PR target/592
	PR middle-end/11135
	* arm.h (struct machine_function): Add pic_reg.
	* arm.c (arm_pic_register): Make unsigned.
	(arm_override_options): Only set arm_pic_register if
	TARGET_SINGLE_PIC_BASE.
	(use_return_insn): Only test for a pic register if it is fixed.
	(arm_compute_save_reg0_reg12_mask): Likewise.
	(thumb_compute_save_reg_mask): Likewise.
	(legitimate_pic_operand): Factor out some known invariants.
	(legitimize_pic_address): If we don't have a fixed pic register,
	then set up a pseudo in the function entry sequence.  Handle the
	pic base being in a pseudo.
	(arm_load_pic_register): Handle the pic register being in a pseudo.
	(arm_expand_prologue): Only set up the pic register if it is fixed.
	(thumb_expand_prologue): Likewise.
	* arm.md (pic_load_addr_based): Handle the pic base being a pseudo.
	(pic_load_addr_based_insn): Likewise.
	(builtin_setjmp_receiver): Don't restore the pic base if it isn't
	fixed.

From-SVN: r109839