------- Additional Comments From ebotcazou at libertysurf dot fr 2005-03-31
06:30 -------
Subject: Re: [3.4 Regression] -fstrict-aliasing causes incorrect scheduling
> I think it's fixable. I'm not sure exactly why the C++ front-end is
> inserting the additional operations, but they're certainly not essential
> from a C++ semantics point of view. Please reassign the bug to me; I'll
> try to take a look.
Thanks, will do. For the records, here's the tree for the first assignment
with the C compiler:
<modify_expr 0x40186390
type <record_type 0x40220074 x_uint64_t type_0 DI
size <integer_cst 0x401797c0 constant 64>
unit size <integer_cst 0x401799e0 constant 8>
align 64 symtab 0 alias set -1
fields <field_decl 0x4021ef68 a type <array_type 0x4021eef4>
DI file ../pr20607.c line 17 size <integer_cst 0x401797c0 64>
unit size <integer_cst 0x401799e0 8>
align 64 offset_align 64
offset <integer_cst 0x40179ac0 constant 0>
bit offset <integer_cst 0x40179b80 constant 0> context
<record_type 0x4021ed24 __x_uint64_t> arguments <integer_cst 0x40179ac0 0>>
context <translation_unit_decl 0x4017c15c>>
side-effects
arg 0 <component_ref 0x40186378 type <record_type 0x40220074 x_uint64_t>
arg 0 <var_decl 0x402205e4 conv type <union_type 0x40220414 u>
used BLK file ../pr20607.c line 31 size <integer_cst 0x401797c0
64> unit size <integer_cst 0x401799e0 8>
align 64 context <function_decl 0x4022015c dotests_1>
(mem/s:BLK (plus:SI (reg/f:SI 103 virtual-stack-vars)
(const_int -16 [0xfffffffffffffff0])) [8 conv+0 S8 A64])>
arg 1 <field_decl 0x402204fc first type <record_type 0x40220074
x_uint64_t>
DI file ../pr20607.c line 28 size <integer_cst 0x401797c0 64>
unit size <integer_cst 0x401799e0 8>
align 64 offset_align 64 offset <integer_cst 0x40179ac0 0> bit
offset <integer_cst 0x40179b80 0> context <union_type 0x40220414 u>
arguments <integer_cst 0x40179ac0 0> chain <field_decl 0x40220570 second>>>
arg 1 <var_decl 0x4022032c arg1 type <record_type 0x40220074 x_uint64_t>
used DI file ../pr20607.c line 23 size <integer_cst 0x401797c0 64>
unit size <integer_cst 0x401799e0 8>
align 64 context <function_decl 0x4022015c dotests_1>
(reg/v:DI 107 [ arg1 ])
chain <var_decl 0x402203a0 result type <record_type 0x4021ecb0
x_uint32_t>
used BLK file ../pr20607.c line 24 size <integer_cst 0x401797c0
64> unit size <integer_cst 0x401799e0 8>
align 64 context <function_decl 0x4022015c dotests_1>
(mem/s:BLK (plus:SI (reg/f:SI 103 virtual-stack-vars)
(const_int -8 [0xfffffffffffffff8])) [2 result+0 S8 A64])>>>
and with the C++ compiler:
<modify_expr 0x40188510
type <record_type 0x40255000 __x_uint64_t type_1 type_5 DI
size <integer_cst 0x401797c0 constant 64>
unit size <integer_cst 0x401799e0 constant 8>
align 64 symtab 0 alias set 2
fields <field_decl 0x402553a0 a type <array_type 0x4025532c>
used nonlocal decl_3 DI file ../pr20607.C line 17 size
<integer_cst 0x401797c0 64> unit size <integer_cst 0x401799e0 8>
align 64 offset_align 64
offset <integer_cst 0x40179ac0 constant 0>
bit offset <integer_cst 0x40179b80 constant 0> context
<record_type 0x40255000 __x_uint64_t> arguments <integer_cst 0x40179ac0 0>
chain <type_decl 0x402551d0 __x_uint64_t>>
X() X(constX&) this=(X&) n_parents 0 use_template=0 interface-unknown
member-functions <tree_vec 0x40253f40
elt 0 <overload 0x402510f0>
elt 2 <function_decl 0x40255cb0 operator=>
elt 3 <overload 0x40251130>
elt 4 <overload 0x40251110>>
pointer_to_this <pointer_type 0x402550e8> reference_to_this
<reference_type 0x40255a6c> chain <type_decl 0x4025515c __x_uint64_t>>
side-effects
arg 0 <indirect_ref 0x402586cc type <record_type 0x40255000 __x_uint64_t>
arg 0 <nop_expr 0x402586b8 type <pointer_type 0x402550e8>
arg 0 <nop_expr 0x402586a4 type <pointer_type 0x402550e8>
arg 0 <non_lvalue_expr 0x40258690 type <pointer_type
0x402599f8>
arg 0 <nop_expr 0x4025867c type <pointer_type 0x402599f8>
arg 0 <addr_expr 0x40258514 type <pointer_type
0x4025789c>
arg 0 <var_decl 0x40259984 conv>>>>>>>
arg 1 <indirect_ref 0x402586e0
type <record_type 0x402556cc __x_uint64_t readonly type_1 type_5 DI
size <integer_cst 0x401797c0 64> unit size <integer_cst 0x401799e0 8>
align 64 symtab 0 alias set -1 fields <field_decl 0x402553a0 a>
X() X(constX&) this=(X&) n_parents 0 use_template=0
interface-unknown member-functions <tree_vec 0x40253f40>
pointer_to_this <pointer_type 0x40259a6c> reference_to_this
<reference_type 0x40255740>>
readonly
arg 0 <nop_expr 0x40258640 type <reference_type 0x40255740>
arg 0 <nop_expr 0x4025862c type <pointer_type 0x40259a6c>
arg 0 <addr_expr 0x40258618 type <pointer_type 0x402599f8>
arg 0 <var_decl 0x40257658 arg1>>>>>>
Type punning needs a COMPONENT_REF to work (see c_common_get_alias_set).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20607
