[Bug rtl-optimization/112995] sel-sched2 ICE without checking verify_changes

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112995

--- Comment #1 from Kewen Lin <linkw at gcc dot gnu.org> ---
Initially we have:

(insn 31 6 10 2 (set (reg/v:SI 9 9 [orig:119 c ] [119])
        (reg/v:SI 64 0 [orig:119 c ] [119])) "test.i":5:5 555
{*movsi_internal1}
     (expr_list:REG_DEAD (reg/v:SI 64 0 [orig:119 c ] [119])
        (nil)))
(insn 10 31 25 2 (set (reg:DI 10 10 [128])
        (ashift:DI (sign_extend:DI (reg/v:SI 9 9 [orig:119 c ] [119]))
            (const_int 2 [0x2]))) "test.i":7:8 278 {ashdi3_extswsli}
     (nil))
(insn 25 10 27 2 (set (reg:DI 64 0 [135])
        (sign_extend:DI (reg/v:SI 9 9 [orig:119 c ] [119]))) "test.i":6:5 31
{extendsidi2}
     (expr_list:REG_DEAD (reg/v:SI 9 9 [orig:119 c ] [119])
        (nil)))

with moving up, we have:

(insn 46 0 0 (set (reg:DI 64 0 [135])
        (sign_extend:DI (reg/v:SI 64 0 [orig:119 c ] [119]))) 31 {extendsidi2}
     (expr_list:REG_DEAD (reg/v:SI 9 9 [orig:119 c ] [119])
        (nil)))

in try_replace_dest_reg, we updated the above EXPR_INSN_RTX to:

(insn 48 0 0 (set (reg:DI 32 0)
        (sign_extend:DI (reg/v:SI 64 0 [orig:119 c ] [119]))) 31 {extendsidi2}
     (nil))

This doesn't match any constraint and it's an unexpected modification.

Unfortunately function try_replace_dest_reg just checks the orig insn with:

      if (REGNO (best_reg) != REGNO (INSN_LHS (orig_insn))
          && (! replace_src_with_reg_ok_p (orig_insn, best_reg)
              || ! replace_dest_with_reg_ok_p (orig_insn, best_reg)))

But it doesn't check EXPR_INSN_RTX, I think it's under the assumption that if
the original insn is able to be replaced then the change on EXPR_INSN_RTX is
fine, but this isn't true as the given test case shows.