[Bug rtl-optimization/88001] New: ASMCONS cannot handle properly UNSPEC(CONST)

[claziss at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88001

            Bug ID: 88001
           Summary: ASMCONS cannot handle properly UNSPEC(CONST)
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: claziss at gmail dot com
  Target Milestone: ---

ASMCONS cannot handle CONST (UNSPEC) properly, leading to a wrong
output.

I have the following rtl before asmcons pass:

(insn 8 13 9 2 (set (reg:SI 157 [ list ])
        (asm_operands:SI ("") ("=g") 0 [
                (const:SI (unspec:SI [
                            (symbol_ref:SI ("c_const") [flags 0x2]  <var_decl
0x7f6735ad25a0 c_const>)
                        ] ARC_UNSPEC_GOTOFFPC))
            ]
             [
                (asm_input:SI ("0") ../t02.c:9)
            ]
             [] ../t02.c:9)) ../t02.c:9 -1
     (nil))

Asmcons pass leads to this:

(insn 13 3 8 2 (set (reg:SI 157 [ list ])
        (const:SI (unspec:SI [
                    (symbol_ref:SI ("c_const") [flags 0x2]  <var_decl
0x7fd69f6365a0 c_const>)
                ] ARC_UNSPEC_GOTOFFPC))) ../t02.c:9 -1
     (nil))
(insn 8 13 9 2 (set (reg:SI 157 [ list ])
        (asm_operands:SI ("") ("=g") 0 [
                (const:SI (unspec:SI [
                            (symbol_ref:SI ("c_const") [flags 0x2]  <var_decl
0x7fd69f6365a0 c_const>)
                        ] ARC_UNSPEC_GOTOFFPC))
            ]
             [
                (asm_input:SI ("0") ../t02.c:9)
            ]
             [] ../t02.c:9)) ../t02.c:9 -1
     (nil))

Which will lead latter on to an ICE when we verify the rtx sharing.

My test program is this one, and it needs to be compiled for ARC backend with
the following options: -mcpu=archs -O2 -fpic

typedef void (*func_ptr) (void);
static func_ptr __DTOR_LIST__[1] = { (func_ptr)(-1) };

void foo (int a)
{
  func_ptr *dtor_list;
  __asm ("" : "=g" (dtor_list) : "0" (__DTOR_LIST__));
  dtor_list[a]();
}