[Bug target/40416] unnecessary register spill

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

------- Comment #2 from ramana at gcc dot gnu dot org  2009-06-12 12:54 -------
(In reply to comment #1)
> Created an attachment (id=17983)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17983&action=view) [edit]
> test case
> 

Your attachment didn't have #include <stdint.h> - Please try and supply
pre-processed input which is self contained . Adding a -I from a build
directory can be rather painful . Thanks - 

> The spilling is occurred around the first loop:
> 
>         push    {r4, r5, r6, r7, lr}
>         sub     sp, sp, #12
>         .loc 1 5 0
>         str     r2, [sp, #4]          // A
>         .loc 1 6 0
>         add     r6, r1, r2
>         mov     r4, r0
>         .loc 1 8 0
>         b       .L2
> .L5:
>         .loc 1 10 0
>         mov     r7, #0
>         ldrsh   r5, [r4, r7]
>         .loc 1 12 0
>         cmp     r2, r5
>         bge     .L3
>         .loc 1 14 0
>         ldrb    r7, [r1]
>         strb    r7, [r1, r2]
>         .loc 1 15 0
>         strh    r2, [r4]
>         .loc 1 16 0
>         lsl     r1, r2, #1
>         sub     r2, r5, r2
>         strh    r2, [r1, r4]
> .L6:
>         .loc 1 5 0
>         ldr     r5, [sp, #4]     //   B
>         lsl     r4, r5, #1
>         add     r0, r0, r4
>         b       .L4
> .L3:
>         .loc 1 19 0
>         lsl     r7, r5, #1
>         mov     ip, r7
>         add     r4, r4, ip
>         .loc 1 20 0
>         add     r1, r1, r5
>         .loc 1 21 0
>         sub     r2, r2, r5
> .L2:
>         .loc 1 8 0
>         cmp     r2, #0
>         bgt     .L5
>         b       .L6
> .L4:
>         .loc 1 30 0
>         mov     r1, #0
> 
> 
> The spilling is occurred at instruction A and reload at instruction B.
> 
> The spilled value is x. The source code computes next_runs and next_alpha
> before while loop and preserve them through the loop body. But the generated
> code preserve next_alpha, original runs and original x through the loop body
> and compute next_runs after the loop. This caused an extra usage of register
> and results in a register spilling.
> 

Could you say what you'd like the code to be because I don't see an option but
to spill one of the values here. ?


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40416