[Bug rtl-optimization/115495] [15 Regression] ICE in smallest_mode_for_size, at stor-layout.cc:356 during combine on RISC-V rv64gcv_zvl256b at -O3

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115495

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-06-14

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Trying 25 -> 26:
   25: r150:DI=r139:V16HI#0 0>>0x10
   26: r151:DI=zero_extend(r150:DI#0)

That is these 2 instructions:
```
(insn 25 24 26 2 (set (reg:DI 150)
        (lshiftrt:DI (subreg:DI (reg:V16HI 139 [ vect_cst__21 ]) 0)
            (const_int 16 [0x10]))) "/app/example.c":5:14 299 {lshrdi3}
     (nil))
(insn 26 25 34 2 (set (reg:DI 151)
        (zero_extend:DI (subreg:HI (reg:DI 150) 0))) "/app/example.c":5:14 121
{*zero_extendhidi2}
     (expr_list:REG_DEAD (reg:DI 150)
        (nil)))
```
The above rtl looks good as far as I know. It looks like
get_best_extraction_insn is using V16HI there though which is where it goes
wrong.

Confirmed.

This comes from the expanision of:
;; MEM <vector(16) short int> [(short int *)&a] = vect_cst__21;

Which looks different for GCC 14.1.0 and much simplier.