Ping #4

This small addition improves costs of PARALLELs in
rtlanal.c:seq_cost().  Up to now, these costs are
assumed to be 1 which gives gross inexact costs for,
e.g. divmod which is represented as PARALLEL.

The patch just forwards cost computation to insn_rtx_cost
which uses the cost of the 1st SET (if any) and otherwise
assign costs of 1 insn.

Bootstrapped & regtested on x86_64.

Moreover, it fixed the division by constant on avr where
the problem popped up since PR79665.

Ok to install?

Johann

gcc/
	PR middle-end/80929
	* rtlanal.c (seq_cost) [PARALLEL]: Get cost from insn_rtx_cost
	instead of assuming cost of 1.