Quoting "Paulo J. Matos" <pocma...@gmail.com>:
Hi all, 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? - or something else?
When optimizing for speed, they estimate execution cycles, when optimizing for space, they estimate code size. In each case, normalized so that COSTS_N_INSNS (1) is equivalent to the cost of a simple instruction. Or at least that's the theoretical goal. Individual ports might deviate from that for historical and/or practical reasons.
