[Bug middle-end/80929] [7/8 Regression] Division with constant no more optimized to mult highpart

["gjl at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80929

--- Comment #6 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
Created attachment 41861
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41861&action=edit
time-i.c: C test case

(In reply to Richard Biener from comment #4)
> Fixed?

No.  The attached test case

$ avr-gcc-8 time-i.c -mmcu=atmega168 -O2 -S -dp

Still uses slow __[u]divmodhi when optimizing for speed.  The code has 2
divisions and modulo with 60.  The first mod is expanded as mul highpart (insn
25) but the second is expanded as __divmodhi4 call (insn 67):

timeid_add:
        ...
        ldi r26,lo8(-119)        ;  24  *movhi/5        [length = 2]
        ldi r27,lo8(-120)
        call __umulhisi3         ;  25  *umulhi3_highpart_call  [length = 2]
        ...
        ldi r22,lo8(16)  ;  61  *movhi/5        [length = 2]
        ldi r23,lo8(14)
        call __udivmodhi4        ;  62  *udivmodhi4_call        [length = 2]
        std Z+2,r22      ;  34  movqi_insn/3    [length = 1]
        movw r24,r18     ;  65  *movhi/1        [length = 1]
        ldi r22,lo8(60)  ;  66  *movhi/5        [length = 2]
        ldi r23,0
        call __divmodhi4         ;  67  *divmodhi4_call [length = 2]
        std Z+1,r24      ;  50  movqi_insn/3    [length = 1]
/* epilogue start */