[4.0 and mainline] Fix multiplication by constant expansion

[Roger Sayle]

On Mon, 2 Jan 2006, Jan Hubicka wrote:
> 2006-01-02  Jan Hubicka  <jh@suse.cz>
> 	* i386.c (*_cost): Add COSTS_N_INSNS.
> 	(ix86_rtx_costs): Do not use COSTS_N_INSNS.

This clean-up/reorganization is OK for mainline, given that it
implements RTH's recommendation for restructuring these tables.
Hopefully, this new infrastructure will simplify the task of
better parameterizing the x86 backends.  Hopefully, RTH will
let me/us know if he's since changed his mind, and I've over
stepped my backend authority and/or your x86_64 maintainership.

Many thanks,

Roger
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