ira: update allocated_hardreg_p[] in improve_allocation() [PR110254]

ira: update allocated_hardreg_p[] in improve_allocation() [PR110254]

The improve_allocation() routine does not update the
allocated_hardreg_p[] array after an allocno is assigned a register.

If the register chosen in improve_allocation() is one that already has
been assigned to a conflicting allocno, then allocated_hardreg_p[]
already has the corresponding bit set to TRUE, so nothing needs to be
done.

But improve_allocation() can also choose a register that has not been
assigned to a conflicting allocno, and also has not been assigned to any
other allocno. In this case, allocated_hardreg_p[] has to be updated.

2023-07-21  Surya Kumari Jangala  <jskumari@linux.ibm.com>

gcc/
	PR rtl-optimization/110254
	* ira-color.cc (improve_allocation): Update array
	allocated_hard_reg_p.