[Bug debug/86455] var-tracking mishandles pre_dec

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86455

--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
Hmm, even more obvious. We push bx to argp - 24:
...
ORIGINAL:
(insn/f 26 3 27 2 (set (mem:DI (pre_dec:DI (reg/f:DI 7 sp)) [0  S8 A8])
        (reg:DI 3 bx)) "clztest.c":12 61 {*pushdi2_rex64}
     (expr_list:REG_DEAD (reg:DI 3 bx)
        (nil)))
ADJUSTED:
(insn/f 26 3 27 2 (parallel [
            (set (mem:DI (plus:DI (reg/f:DI 16 argp)
                        (const_int -24 [0xffffffffffffffe8])) [0  S8 A8])
                (reg:DI 3 bx))
            (set (reg/f:DI 7 sp)
                (plus:DI (reg/f:DI 16 argp)
                    (const_int -24 [0xffffffffffffffe8])))
        ]) "clztest.c":12 61 {*pushdi2_rex64}
     (expr_list:REG_DEAD (reg:DI 3 bx)
        (nil)))
...

but pop bx from argp - 16:
...
ORIGINAL:
(insn/f 29 28 30 2 (set (reg:DI 3 bx)
        (mem:DI (post_inc:DI (reg/f:DI 7 sp)) [0  S8 A8])) "clztest.c":17 71
{*popdi1}
     (expr_list:REG_CFA_ADJUST_CFA (set (reg/f:DI 7 sp)
            (plus:DI (reg/f:DI 7 sp)
                (const_int 8 [0x8])))
        (nil)))
ADJUSTED:
(insn/f 29 28 30 2 (parallel [
            (set (reg:DI 3 bx)
                (mem:DI (plus:DI (reg/f:DI 16 argp)
                        (const_int -16 [0xfffffffffffffff0])) [0  S8 A8]))
            (set (reg/f:DI 7 sp)
                (plus:DI (reg/f:DI 16 argp)
                    (const_int -8 [0xfffffffffffffff8])))
        ]) "clztest.c":17 71 {*popdi1}
     (expr_list:REG_CFA_ADJUST_CFA (set (reg/f:DI 7 sp)
            (plus:DI (reg/f:DI 7 sp)
                (const_int 8 [0x8])))
        (nil)))
...