RTX costs

[Richard Kenner]

> After reading the internal docs about rtx_costs I am left wondering what 
> they exactly are estimating.
> - Are they estimating in the beginning of expand how many insns will be 
> generated from a particular insn until the assembler is generated?
> - or Are they estimating how many assembler instructions will be 
> generated for a particular insn?

The latter is what they're *supposed* to be measuring, but of course it's
an approximation.