[Bug target/9663] [arm] gcc-20030127 misses an optimization opportunity

[ramana dot r at gmail dot com]

------- Comment #8 from ramana dot r at gmail dot com  2009-02-08 05:17 -------
(In reply to comment #7)
> Note you have to do with -fno-inline now on the mainline as the function is
> inlined at -O2.
> 

It looks as though this is fixed in 4.3 and mainline today. I checked with 4.1
and saw that the problem existed in 4.1 


Looking at the assembly generated for the function, I no longer see a cmp and
mov as reported in the bug report. I see similar code generated in 4.1 but no
longer in 4.3 or 4.4. I see subs generated for 4.3 and 4.4 in the loop kernel
as of version r143940 for 4.3 and 144002 for mainline. 

Here is the snippet of code from 4.1, 4.3 and 4.4 as given below.


4.1 

.L8:
        ldr     r3, .L12
        umull   r1, r2, r3, ip
        mov     r2, r2, lsr #3
        mov     r3, r2, asl #1
        mov     r1, r2, asl #3
        add     r3, r3, r1
        rsb     r3, r3, ip
        add     r3, r3, #48
        cmp     r2, #0            ---- Insns from original bug report.
        mov     ip, r2            ----
        strb    r3, [r0, #-1]!
        bne     .L8



4.3
.L5:
        umull   r2, r3, r5, ip
        mov     r3, r3, lsr #3
        mov     r2, r3, asl #1
        mov     r1, r3, asl #3
        add     r2, r2, r1
        rsb     r2, r2, ip
        add     r2, r2, #48
        subs    ip, r3, #0
        strb    r2, [r0, #-1]!
        bne     .L5





4.4 

  .L5:
        umull   r1, r2, r4, ip
        mov     r2, r2, lsr #3
        add     r1, r2, r2, asl #2
        sub     ip, ip, r1, asl #1
        add     r1, ip, #48
        subs    ip, r2, #0
        strb    r1, [r0, #-1]!
        bne     .L5


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=9663