On Tue, Feb 14, 2012 at 11:51 PM, Richard Henderson <r...@redhat.com> wrote: > On 02/14/2012 02:08 PM, Steven Bosscher wrote: >> OK for trunk? > > This can wait for stage1. > >> +;; On PDP-11, DIV always produces a quotient and a remainder. But CSE >> +;; cannot optimize the divmods away because the SET_DESTs are SUBREGs. >> +; >> ;(define_expand "divmodhi4" >> ; [(parallel [(set (subreg:HI (match_dup 1) 0) > > Which of course begs the question of why that's so. > The division patterns can be modeled similarly to s390.
That is what Ian also said on IRC, but I didn't want to go that far (I didn't think this basically cosmetic change would be a problem for stage4 but rewriting patterns, even for a pet target like this, didn't seem appropriate). Anyway, history for this goes back a long long time: http://gcc.gnu.org/viewcvs?view=revision&revision=10175 The previous div/mod/divmod patterns didn't have subregs. For example: (define_expand "divhi3" - [(set (match_dup 3) - (sign_extend:SI (match_operand:HI 1 "general_operand" "g"))) - (set (match_operand:HI 0 "general_operand" "g") - (truncate:HI - (div:SI - (match_dup 3) - (sign_extend:SI (match_operand:HI 2 "general_operand" "g")))))] - "TARGET_45" - "operands[3] = gen_reg_rtx (SImode);") Not sure why this was changed. What I'd like to do, is remove the divhi3 and movhi3 define_expand and define_insn, and just keep divmodhi4. You point to s390. I suppose you mean the divmoddi4 expander there? > Indeed, all of the appearances of subreg in the md file are errors: I was only playing with your match_flags patches. I get the feeling I am going to regret that... :-) > Should be removed as unnecessary: > > (define_expand "truncsihi2" > > Should be removed as generated by generic code: > > (define_insn "zero_extendqihi2" > (define_expand "zero_extendhisi2" What do you mean with "generated by generic code"? And the define_insn has to stay, surely? Thanks, and sorry for the novice questions! Ciao! Steven
