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* [Bug ada/12966] New: x86 array comparison optimization
@ 2003-11-08 18:15 dave at synergy dot org
2003-11-08 18:24 ` [Bug ada/12966] " pinskia at gcc dot gnu dot org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: dave at synergy dot org @ 2003-11-08 18:15 UTC (permalink / raw)
To: gcc-bugs
gnatmake -O3 q
See OPTIMIZE below.
Ada source:
with Ada.Text_IO;
use Ada.Text_IO;
procedure Q is
type Unsigned_32 is
mod 2 ** 32;
type A_Type is
array (1..4) of Unsigned_32;
X: A_Type := (0, 0, 0, 0);
Y: A_Type := (0, 0, 0, 0);
begin
if X = Y then
Put_Line(Standard_Output, "=");
else
Put_Line(Standard_Output, "/=");
end if;
end Q;
x86 object:
q.o: file format elf32-i386
Disassembly of section .text:
--
-- procedure Q is
-- begin
--
00000000 <_ada_q>:
0: 55 push %ebp
6: 89 e5 mov %esp,%ebp
b: 83 ec 38 sub $0x38,%esp
e: 89 7d fc mov %edi,0xfffffffc(%ebp)
16: 89 75 f8 mov %esi,0xfffffff8(%ebp)
--
-- X := (0, 0, 0, 0);
--
8: fc cld
9: 31 c0 xor %eax,%eax
1: ba 04 00 00 00 mov $0x4,%edx
11: 89 d1 mov %edx,%ecx
13: 8d 7d e8 lea 0xffffffe8(%ebp),%edi
1c: f3 ab repz stos %eax,%es:(%edi)
--
-- Y := (0, 0, 0, 0);
--
21: 89 d1 mov %edx,%ecx
1e: 8d 7d d8 lea 0xffffffd8(%ebp),%edi
23: f3 ab repz stos %eax,%es:(%edi)
--
-- OPTIMIZE
--
-- if X = Y then
--
-- In the previous two sequences we knew enough to use stosl loops
-- to initialize the X and Y arrays. In this sequence we're comparing the
-- same two arrays for equality. However, this sequence reverts to a
-- cmpsb (not a cmpsl) loop. There is a 4:1 execution penalty for making
-- this decision with no impact on code size.
--
28: b9 10 00 00 00 mov $0x10,%ecx
19: 8d 75 d8 lea 0xffffffd8(%ebp),%esi
25: 8d 7d e8 lea 0xffffffe8(%ebp),%edi
2d: f3 a6 repz cmpsb %es:(%edi),%ds:(%esi)
--
-- Put_Line(Standard_Output, "=");
--
2f: 75 2f jne 60 <_ada_q+0x60>
31: e8 fc ff ff ff call 32 <_ada_q+0x32>
32: R_386_PC32 ada__text_io__standard_output
36: ba 10 00 00 00 mov $0x10,%edx
37: R_386_32 .rodata
3b: b9 00 00 00 00 mov $0x0,%ecx
3c: R_386_32 .rodata
40: 89 54 24 04 mov %edx,0x4(%esp,1)
44: 89 4c 24 08 mov %ecx,0x8(%esp,1)
48: 89 04 24 mov %eax,(%esp,1)
4b: e8 fc ff ff ff call 4c <_ada_q+0x4c>
4c: R_386_PC32 ada__text_io__put_line
--
-- end if;
-- end Q;
--
50: 8b 75 f8 mov 0xfffffff8(%ebp),%esi
53: 8b 7d fc mov 0xfffffffc(%ebp),%edi
56: 89 ec mov %ebp,%esp
58: 5d pop %ebp
59: c3 ret
--
-- Put_Line(Standard_Output, "/=");
--
5a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
60: e8 fc ff ff ff call 61 <_ada_q+0x61>
61: R_386_PC32 ada__text_io__standard_output
65: ba 11 00 00 00 mov $0x11,%edx
66: R_386_32 .rodata
6a: b9 08 00 00 00 mov $0x8,%ecx
6b: R_386_32 .rodata
6f: eb cf jmp 40 <_ada_q+0x40>
--
Summary: x86 array comparison optimization
Product: gcc
Version: 3.3.2
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: ada
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: dave at synergy dot org
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12966
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2005-04-07 7:59 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2003-11-08 18:15 [Bug ada/12966] New: x86 array comparison optimization dave at synergy dot org
2003-11-08 18:24 ` [Bug ada/12966] " pinskia at gcc dot gnu dot org
2004-08-12 1:51 ` pinskia at gcc dot gnu dot org
2004-10-29 14:05 ` [Bug middle-end/12966] " pinskia at gcc dot gnu dot org
2005-04-07 7:59 ` pinskia at gcc dot gnu dot org
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