[Bug tree-optimization/42248] compat test struct-by-value-17 fails execution with -O1 -fschedule-insns

["pthaugen at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #3 from pthaugen at gcc dot gnu dot org  2010-01-13 22:11 -------
Created an attachment (id=19585)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19585&action=view)
Testcase

Adding a shortened executable testcase that still fails.

This looks like an aliasing issue. We're not creating a dependency between a
store and load of a memory location which then allows the scheduler to reorder
the insns.

(insn 2 9 3 2 test.c:10 (set (mem/s/c:DI (plus:DI (reg/f:DI 67 ap)
                (const_int 48 [0x30])) [0 x+0 S8 A64])
        (reg:DI 3 3)) 373 {*movdi_internal64} (expr_list:REG_DEAD (reg:DI 3 3)
        (nil)))
...
(insn 11 8 12 2 test.c:10 (set (reg:DF 126 [ x$a ])
        (mem/s/j/c:DF (plus:DI (reg/f:DI 67 ap)
                (const_int 48 [0x30])) [0 x.a+0 S8 A64])) 360
{*movdf_hardfloat64} (nil))


Some debug data along the dependency creation/alias checking path:

Breakpoint 4, true_dependence (mem=0x40000357068, mem_mode=DImode,
x=0x400003571d0, 
    varies=@0x112aa168: 0x106737c4 <rtx_varies_p>) at
/home/pthaugen/src/gcc/trunk/gcc/gcc/alias.c:2367
2367      return rtx_refs_may_alias_p (x, mem, true);
(gdb) pr x
(mem/s/j/c:DF (plus:DI (reg/f:DI 67 ap)
        (const_int 48 [0x30])) [0 x.a+0 S8 A64])
(gdb) pr mem
(mem/s/c:DI (plus:DI (reg/f:DI 67 ap)
        (const_int 48 [0x30])) [0 x+0 S8 A64])

We then go through rtx_refs_may_alias_p() -> refs_may_alias_p_1() ->
decl_refs_may_alias_p() which contains the following code where we return
false.

  /* If both references are based on different variables, they cannot alias. 
*/
  if (!operand_equal_p (base1, base2, 0))
    return false;

Breakpoint 7, operand_equal_p (arg0=0x40000370110, arg1=0x40000370660, flags=0)
    at /home/pthaugen/src/gcc/trunk/gcc/gcc/fold-const.c:3160
3160      if (TREE_CODE (arg0) == ERROR_MARK || TREE_CODE (arg1) == ERROR_MARK)

(gdb) prt arg0
 <parm_decl 0x40000370110 x
    type <record_type 0x4000042cac8 Scf10 type_0 BLK
        size <integer_cst 0x400002d0e10 constant 256>
        unit size <integer_cst 0x400002d0460 constant 32>
        align 64 symtab 0 alias set -1 canonical type 0x4000042ca20
        fields <field_decl 0x40000450c78 a type <complex_type 0x400003b1c38
complex double>
            DC file test.c line 2 col 19
            size <integer_cst 0x400002d0a50 constant 128>
            unit size <integer_cst 0x400002d0a78 constant 16>
            align 64 offset_align 128
            offset <integer_cst 0x400002d04b0 constant 0>
            bit offset <integer_cst 0x400002d0b90 constant 0> context
<record_type 0x4000042ca20> chain <field_decl 0x40000450d10 b>> context
<translation_unit_decl 0x400003d26d0 D.1272>
        pointer_to_this <pointer_type 0x4000042ce10> chain <type_decl
0x400003d2560 D.1257>>
    used BLK file test.c line 9 col 14 size <integer_cst 0x400002d0e10 256>
unit size <integer_cst 0x400002d0460 32>
    align 64 context <function_decl 0x4000044a700 check>
    (mem/s/c:BLK (plus:DI (reg/f:DI 67 ap)
        (const_int 48 [0x30])) [0 x+0 S32 A64]) arg-type <record_type
0x4000042cac8 Scf10>
    incoming-rtl (reg:DI 3 3 [ x+-8 ]) chain <parm_decl 0x40000370198 y>>
(gdb) prt arg1
 <parm_decl 0x40000370660 x
    type <record_type 0x4000042cac8 Scf10 type_0 BLK
        size <integer_cst 0x400002d0e10 constant 256>
        unit size <integer_cst 0x400002d0460 constant 32>
        align 64 symtab 0 alias set -1 canonical type 0x4000042ca20
        fields <field_decl 0x40000450c78 a type <complex_type 0x400003b1c38
complex double>
            DC file test.c line 2 col 19
            size <integer_cst 0x400002d0a50 constant 128>
            unit size <integer_cst 0x400002d0a78 constant 16>
            align 64 offset_align 128
            offset <integer_cst 0x400002d04b0 constant 0>
            bit offset <integer_cst 0x400002d0b90 constant 0> context
<record_type 0x4000042ca20> chain <field_decl 0x40000450d10 b>> context
<translation_unit_decl 0x400003d26d0 D.1272>
        pointer_to_this <pointer_type 0x4000042ce10> chain <type_decl
0x400003d2560 D.1257>>
    used BLK file test.c line 9 col 14 size <integer_cst 0x400002d0e10 256>
unit size <integer_cst 0x400002d0460 32>
    align 64 context <function_decl 0x4000044a700 check>
    (mem/s/c:BLK (plus:DI (reg/f:DI 67 ap)
        (const_int 48 [0x30])) [0 x+0 S32 A64]) arg-type <record_type
0x4000042cac8 Scf10>
    incoming-rtl (reg:DI 3 3 [ x+-8 ]) chain <parm_decl 0x400003706e8 y>>


In operand_equal_p() we get to the following which returns false:

    case tcc_declaration:
      /* Consider __builtin_sqrt equal to sqrt.  */
      return (TREE_CODE (arg0) == FUNCTION_DECL
              && DECL_BUILT_IN (arg0) && DECL_BUILT_IN (arg1)
              && DECL_BUILT_IN_CLASS (arg0) == DECL_BUILT_IN_CLASS (arg1)
              && DECL_FUNCTION_CODE (arg0) == DECL_FUNCTION_CODE (arg1));


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42248