On Tue, Jun 30, 2015 at 02:16:19PM +0930, Alan Modra wrote: > On Mon, Jun 29, 2015 at 09:34:40AM -0500, Segher Boessenkool wrote: > > On Mon, Jun 29, 2015 at 05:16:39PM +0930, Alan Modra wrote: > > > Note that we already have insn_rtx_cost, and it returns a minimum cost > > > for a SET, so register move insns get a cost of 1 insn. However, > > > despite insn_rtx_cost starting life in combine.c, even combine doesn't > > > use it in all whole insn cases. :-( > > > > In what cases does it not? > > Practically all of the occurrences of set_src_cost in combine.c can be > called on whole insns. By "whole insn" I mean of course the right > hand side of a set, or a single set inside a parallel. I'm not saying > that this causes trouble, since I haven't seen a register move there > (but I haven't looked very hard either).
All (all five) places in combine where it uses set_src_cost it is comparing two possible simplifications, to see if they are simplifications at all. So all is good as far as I see -- certainly simplifying anything to just a register is the best you can do, so a cost of 0 for that is fine. For all instructions (including those that are not single sets) combine uses insn_rtx_cost to decide the cost of the whole instructions, to see if the final instruction combination it came up with is profitable. insn_rtx_cost could certainly use some improvement though :-/ Segher
