target/109650: Fix wrong code after cc0 -> CCmode transition.

This patch fixes a wrong-code bug in the wake of PR92729, the transition that
turned the AVR backend from cc0 to CCmode.  In cc0, the insn that uses cc0 like
a conditional branch always follows the cc0 setter, which is no more the case
with CCmode where set and use of REG_CC might be in different basic blocks.

This patch removes the machine-dependent reorg pass in avr_reorg entirely.

It is replaced by a new, AVR specific mini-pass that runs prior to split2.
Canonicalization of comparisons away from the "difficult" codes GT[U] and LE[U]
is now mostly performed by implementing TARGET_CANONICALIZE_COMPARISON.

Moreover:

* Text peephole conditions get "dead_or_set_regno_p (*, REG_CC)" as needed.

* RTL peephole conditions get "peep2_regno_dead_p (*, REG_CC)" as needed.

* Conditional branches no more clobber REG_CC.

* insn output for compares looks ahead to determine the branch mode in use.
  This needs also "dead_or_set_regno_p (*, REG_CC)".

* Add RTL peepholes for decrement-and-branch detection.

* Some of the patterns like "*cmphi.zero-extend.0" lost their
  combine-ational part wit PR92729.  Restore them.

Finally, it fixes some of the many indentation glitches left over from PR92729.

gcc/
	PR target/109650
	PR target/92729
	* config/avr/avr-passes.def (avr_pass_ifelse): Insert new pass.
	* config/avr/avr.cc (avr_pass_ifelse): New RTL pass.
	(avr_pass_data_ifelse): New pass_data for it.
	(make_avr_pass_ifelse, avr_redundant_compare, avr_cbranch_cost)
	(avr_canonicalize_comparison, avr_out_plus_set_ZN)
	(avr_out_cmp_ext): New functions.
	(compare_condtition): Make sure REG_CC dies in the branch insn.
	(avr_rtx_costs_1): Add computation of cbranch costs.
	(avr_adjust_insn_length) [ADJUST_LEN_ADD_SET_ZN, ADJUST_LEN_CMP_ZEXT]:
	[ADJUST_LEN_CMP_SEXT]Handle them.
	(TARGET_CANONICALIZE_COMPARISON): New define.
	(avr_simplify_comparison_p, compare_diff_p, avr_compare_pattern)
	(avr_reorg_remove_redundant_compare, avr_reorg): Remove functions.
	(TARGET_MACHINE_DEPENDENT_REORG): Remove define.
	* config/avr/avr-protos.h (avr_simplify_comparison_p): Remove proto.
	(make_avr_pass_ifelse, avr_out_plus_set_ZN, cc_reg_rtx)
	(avr_out_cmp_zext): New Protos
	* config/avr/avr.md (branch, difficult_branch): Don't split insns.
	(*cbranchhi.zero-extend.0", *cbranchhi.zero-extend.1")
	(*swapped_tst<mode>, *add.for.eqne.<mode>): New insns.
	(*cbranch<mode>4): Rename to cbranch<mode>4_insn.
	(define_peephole): Add dead_or_set_regno_p(insn,REG_CC) as needed.
	(define_deephole2): Add peep2_regno_dead_p(*,REG_CC) as needed.
	Add new RTL peepholes for decrement-and-branch and *swapped_tst<mode>.
	Rework signtest-and-branch peepholes for *sbrx_branch<mode>.
	(adjust_len) [add_set_ZN, cmp_zext]: New.
	(QIPSI): New mode iterator.
	(ALLs1, ALLs2, ALLs4, ALLs234): New mode iterators.
	(gelt): New code iterator.
	(gelt_eqne): New code attribute.
	(rvbranch, *rvbranch, difficult_rvbranch, *difficult_rvbranch)
	(branch_unspec, *negated_tst<mode>, *reversed_tst<mode>)
	(*cmpqi_sign_extend): Remove insns.
	(define_c_enum "unspec") [UNSPEC_IDENTITY]: Remove.
	* config/avr/avr-dimode.md (cbranch<mode>4): Canonicalize comparisons.
	* config/avr/predicates.md (scratch_or_d_register_operand): New.
	* config/avr/constraints.md (Yxx): New constraint.

gcc/testsuite/
	PR target/109650
	* gcc.target/avr/torture/pr109650-1.c: New test.
	* gcc.target/avr/torture/pr109650-2.c: New test.

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