On Thu, Oct 15, 2015 at 09:19:49AM +0100, Kyrill Tkachov wrote: > >I can see all the fprintf in combine.c but I just dont know how to triggle > >the dump. > > If you specify -fdump-rtl-combine on the command line gcc will create a > dump file > with the information that combine dumps. > > Usually I just dump all rtl passes with -da. You can also use -fdump-rtl-combine-details to view whatever the pass considers to be "the details", just like with tree dumps. Unfortunately this seems to not be documented. For combine, all the combination attempts are printed with this, which is usually the more interesting information. Combine then also prints the costs of all potential combinations (it uses insn_rtx_cost as the cost: if the insn is a single SET, or a PARALLEL of a single SET (and other things), it computes set_src_cost of the src of that set; if positive, it returns that; otherwise, COST_N_INSNS (1); in other cases (not a single set) it returns 0). You can also use -fdump-rtl-combine-all to just have it print *everything*, often the best thing to do. -da is -fdump-rtl-all-all. I recommend -da (and cleaning up after yourself, there are rather many dumps ;-) ) Segher
