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

[mans at mansr dot com]

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.