[Bug target/55026] Useless stores generated for structures passed by value

["mans at mansr dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55026

--- Comment #3 from Mans Rullgard <mans at mansr dot com> 2012-10-22 19:34:25 UTC ---
It has actually got worse over time.  With 4.3 I get this:

f:
        sub     sp, sp, #8
        mov     r2, r0
        stmia   sp, {r0, r1}
        add     r0, r1, r2
        add     sp, sp, #8
        bx      lr

Here it's only doing the stores, not the loads, and it does them using sp
directly.

With 4.4 and 4.5 it gets slightly worse:

f:
        sub     sp, sp, #8
        mov     r3, sp
        stmia   r3, {r0, r1}
        mov     r3, r0
        add     r0, r1, r3
        add     sp, sp, #8
        bx      lr

Now it's copying sp to another register used as base address in the store.  The
load is still absent.

4.6 and later produce the code I quoted originally.  I can't say I like the
trend.