RA: Implement reuse of equivalent memory for caller saves optimization

RA: Implement reuse of equivalent memory for caller saves optimization

The test case shows opportunity to reuse memory with constant address for
caller saves optimization for constant or pure function call.  The patch
implements the memory reuse.

        PR rtl-optimization/103541

gcc/ChangeLog:

	* ira.h (struct ira_reg_equiv_s): Add new field caller_save_p.
	* ira.cc (validate_equiv_mem): Check memref address variance.
	(update_equiv_regs): Define caller save equivalence for
	valid_combine.
	(setup_reg_equiv): Clear defined_p flag for caller save equivalence.
	* lra-constraints.cc (lra_copy_reg_equiv): Add new arg
	call_save_p.  Use caller save equivalence depending on the arg.
	(split_reg): Adjust the call.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr103541.c: New.