Calculation of RTX Costs

[Paulo J. Matos]

Hello,

I would like some clarification on the meaning of RTX Costs.
When optimising for speed I assume they estimate the time at which the
final generated code is going to take to execute for each rtx.
When optimising for size it is the estimated number of words that each
rtx will generate in the final image. Is this correct?

Moreover, is there a reason for the existence of COST_N_INSNS(x) and why
this multiplies x by 4? Is 4 just a special number? Any reason on why I
should be using COST_N_INSNS instead of just assigning *total (of
target_rtx_costs) to a simple integer?

Cheers,

-- 
PMatos