[PR67753] fix copy of PARALLEL entry_parm to CONCAT target_reg

[PR67753] fix copy of PARALLEL entry_parm to CONCAT target_reg

In assign_parms_setup_block, the copy of args in PARALLELs from
entry_parm to stack_parm is deferred to the parm conversion insn seq,
but the copy from stack_parm to target_reg was inserted in the normal
copy seq, that is executed before the conversion insn seq.  Oops.

We could do away with the need for an actual stack_parm in general,
which would have avoided the need for emitting the copy to target_reg
in the conversion seq, but at least on pa, due to the need for stack
to copy between SI and SF modes, it seems like using the reserved
stack slot is beneficial, so I put in logic to use a pre-reserved
stack slot when there is one, and emit the copy to target_reg in the
conversion seq if stack_parm was set up there.

for  gcc/ChangeLog

	PR rtl-optimization/67753
	PR rtl-optimization/64164
	* function.c (assign_parm_setup_block): Avoid allocating a
	stack slot if we don't have an ABI-reserved one.  Emit the
	copy to target_reg in the conversion seq if the copy from
	entry_parm is in it too.  Don't use the conversion seq to copy
	a PARALLEL to a REG or a CONCAT.

From-SVN: r229840