[Bug tree-optimization/14841] [tree-ssa] const_array[CST] is not folded

[steven at gcc dot gnu dot org]

------- Additional Comments From steven at gcc dot gnu dot org  2004-09-03 21:48 -------
What makes the general case with more fields a bit hard is that you apparently need to 
traverse the component/array ref list to the innermost reference to find the referenced variable.  
Otherwise there is to way to see if the component/array ref references a constant initializer.  
Like so: 
 
(gdb) p debug_tree (*stmt_p) 
 <modify_expr 0x2a95595870 
    type <integer_type 0x2a955968c0 int public SI 
        size <integer_cst 0x2a955949c0 constant invariant 32> 
        unit size <integer_cst 0x2a95594420 constant invariant 4> 
        align 32 symtab 0 alias set 4 precision 32 min <integer_cst 0x2a95594960 -2147483648> 
max <integer_cst 0x2a95594990 2147483647> 
        pointer_to_this <pointer_type 0x2a955b0540>> 
    side-effects 
    arg 0 <var_decl 0x2a959238c0 T.0 type <integer_type 0x2a955968c0 int> 
        used ignored SI file t.c line 12 size <integer_cst 0x2a955949c0 32> unit size 
<integer_cst 0x2a95594420 4> 
        align 32 context <function_decl 0x2a95923540 main>> 
    arg 1 <component_ref 0x2a95595820 type <integer_type 0x2a955968c0 int> 
 
        arg 0 <component_ref 0x2a955957d0 type <record_type 0x2a9590fe00 b> 
            arg 0 <var_decl 0x2a959232a0 t> arg 1 <field_decl 0x2a959230e0 b>> 
        arg 1 <field_decl 0x2a95923000 i type <integer_type 0x2a955968c0 int> 
            SI file t.c line 3 size <integer_cst 0x2a955949c0 32> unit size <integer_cst 
0x2a95594420 4> 
            align 32 offset_align 128 
            offset <integer_cst 0x2a95594450 constant invariant 0> 
            bit offset <integer_cst 0x2a955aa810 constant invariant 0> context <record_type 
0x2a9590fe00 b> arguments <integer_cst 0x2a95594450 0>>> 
    t.c:12> 
$11 = void 
(gdb) p debug_tree (rhs) 
 <component_ref 0x2a95595820 
    type <integer_type 0x2a955968c0 int public SI 
        size <integer_cst 0x2a955949c0 constant invariant 32> 
        unit size <integer_cst 0x2a95594420 constant invariant 4> 
        align 32 symtab 0 alias set 4 precision 32 min <integer_cst 0x2a95594960 -2147483648> 
max <integer_cst 0x2a95594990 2147483647> 
        pointer_to_this <pointer_type 0x2a955b0540>> 
 
    arg 0 <component_ref 0x2a955957d0 
        type <record_type 0x2a9590fe00 b type_0 SI size <integer_cst 0x2a955949c0 32> unit 
size <integer_cst 0x2a95594420 4> 
            align 32 symtab 0 alias set 3 fields <field_decl 0x2a95923000 i> context 
<translation_unit_decl 0x2a959239a0> 
            chain <type_decl 0x2a9590fee0>> 
 
        arg 0 <var_decl 0x2a959232a0 t type <record_type 0x2a9590fc40 a> 
            asm_written used public static SI file t.c line 7 size <integer_cst 0x2a955949c0 32> 
unit size <integer_cst 0x2a95594420 4> 
            align 32 initial <constructor 0x2a95634340> 
            (mem/s:SI (symbol_ref:DI ("t") [flags 0x2] <var_decl 0x2a959232a0 t>) [2 t+0 S4 A32]) 
chain <function_decl 0x2a95923540 main>> 
        arg 1 <field_decl 0x2a959230e0 b type <record_type 0x2a9590fe00 b> 
            SI file t.c line 4 size <integer_cst 0x2a955949c0 32> unit size <integer_cst 
0x2a95594420 4> 
            align 32 offset_align 128 
            offset <integer_cst 0x2a95594450 constant invariant 0> 
            bit offset <integer_cst 0x2a955aa810 constant invariant 0> context <record_type 
0x2a9590fc40 a> arguments <integer_cst 0x2a95594450 0>>> 
    arg 1 <field_decl 0x2a95923000 i type <integer_type 0x2a955968c0 int> 
        SI file t.c line 3 size <integer_cst 0x2a955949c0 32> unit size <integer_cst 
0x2a95594420 4> 
        align 32 offset_align 128 offset <integer_cst 0x2a95594450 0> bit offset <integer_cst 
0x2a955aa810 0> context <record_type 0x2a9590fe00 b> arguments <integer_cst 
0x2a95594450 0>>> 
$12 = void 
(gdb) p rhs->common.constant_flag 
$13 = 0 
(gdb) p debug_tree (rhs->exp.operands[0]->exp.operands[0]) 
 <var_decl 0x2a959232a0 t 
    type <record_type 0x2a9590fc40 a type_0 SI 
        size <integer_cst 0x2a955949c0 constant invariant 32> 
        unit size <integer_cst 0x2a95594420 constant invariant 4> 
        align 32 symtab 0 alias set 2 
        fields <field_decl 0x2a959230e0 b type <record_type 0x2a9590fe00 b> 
            SI file t.c line 4 size <integer_cst 0x2a955949c0 32> unit size <integer_cst 
0x2a95594420 4> 
            align 32 offset_align 128 
            offset <integer_cst 0x2a95594450 constant invariant 0> 
            bit offset <integer_cst 0x2a955aa810 constant invariant 0> context <record_type 
0x2a9590fc40 a> arguments <integer_cst 0x2a95594450 0>> context <translation_unit_decl 
0x2a959239a0> 
        chain <type_decl 0x2a9590fd20>> 
    asm_written used public static SI file t.c line 7 size <integer_cst 0x2a955949c0 32> unit 
size <integer_cst 0x2a95594420 4> 
    align 32 initial <constructor 0x2a95634340> 
    (mem/s:SI (symbol_ref:DI ("t") [flags 0x2] <var_decl 0x2a959232a0 t>) [2 t+0 S4 A32]) 
chain <function_decl 0x2a95923540 main>> 
$14 = void 
 
Either we should somehow mark the component ref itself as constant, or we have to traverse 
the (in this case) COMPONENT_REF to the innermost reference to see the variable that is 
referenced.  That might actually get pretty expensive, I'd think...??? 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14841