[Bug target/77308] surprisingly large stack usage for sha512 on arm

["bernd.edlinger at hotmail dot de" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77308

--- Comment #7 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
even more surprisingly is that:

While thumb2 code (-march=armv6t2 -mthumb) has about the same stack size
as arm code (-marm), thumb1 code has only 1588 bytes stack, and it does
not change with -fno-schedule-insns nor with the patch above:

arm-unknown-eabi-gcc -O3 -march=armv6 -msoft-float -mthumb -S sha512.c

=>

sha512_block_data_order:
        push    {r4, r5, r6, r7, lr}
        mov     r6, r10
        mov     r4, r8
        mov     r7, fp
        mov     r5, r9
        ldr     r3, .L11
        push    {r4, r5, r6, r7}
        ldr     r4, .L11+4
        add     sp, sp, r4

...

.L11:
        .word   1580
        .word   -1588