modulo-sched: Carefully process loop counter initialization [PR97421]

modulo-sched: Carefully process loop counter initialization [PR97421]

Do not allow direct adjustment of pre-header initialization instruction for
count register if is read in some instruction below in that basic block.

gcc/ChangeLog:

	PR rtl-optimization/97421
	* modulo-sched.c (generate_prolog_epilog): Remove forward
	declaration, adjust last argument name and type.
	(const_iteration_count): Add bool pointer parameter to return
	whether count register is read in pre-header after its
	initialization.
	(sms_schedule): Fix count register initialization adjustment
	procedure according to what const_iteration_count said.

gcc/testsuite/ChangeLog:

	PR rtl-optimization/97421
	* gcc.c-torture/execute/pr97421-1.c: New test.
	* gcc.c-torture/execute/pr97421-2.c: New test.
	* gcc.c-torture/execute/pr97421-3.c: New test.

(cherry picked from commit 4eb8f93d026eaa1de9b4820337069f3ce3465cd0)