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* [Bug rtl-optimization/16541] code quality issue for bit manipulations with 64bit
[not found] <bug-16541-1008@http.gcc.gnu.org/bugzilla/>
@ 2008-09-14 4:21 ` pinskia at gcc dot gnu dot org
0 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2008-09-14 4:21 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from pinskia at gcc dot gnu dot org 2008-09-14 04:20 -------
IRA produces even worse code ...
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16541
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug rtl-optimization/16541] code quality issue for bit manipulations with 64bit
[not found] <bug-16541-4@http.gcc.gnu.org/bugzilla/>
@ 2011-05-22 15:51 ` steven at gcc dot gnu.org
0 siblings, 0 replies; 6+ messages in thread
From: steven at gcc dot gnu.org @ 2011-05-22 15:51 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16541
Steven Bosscher <steven at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
--- Comment #6 from Steven Bosscher <steven at gcc dot gnu.org> 2011-05-22 15:21:05 UTC ---
(In reply to comment #2)
> Here is a simplified test case that shows a code quality regression:
>
> extern unsigned char first_one[65536];
> int FirstOnet(unsigned long long arg1)
> {
> if (arg1 >> 48)
> return (first_one[arg1 >> 48]);
> return 0;
> }
>
> the code generated by gcc-3.0 -O2 -fomit-frame-pointer is:
>
> movl 8(%esp), %edx
> movl %edx, %eax
> shrl $16, %eax
> xorl %edx, %edx
> movl %eax, %ecx
> orl %edx, %ecx
> je .L3
> movzbl first_one(%eax), %eax
> ret
> .p2align 2
> .L3:
> xorl %eax, %eax
> ret
>
> and by mainline (a bit worse):
>
> pushl %ebx <- using a callee saved register
> xorl %ecx, %ecx
> movl 12(%esp), %edx
> movl %edx, %eax <- why not load directly to eax?
> xorl %edx, %edx
> shrl $16, %eax
> movl %edx, %ebx
> orl %eax, %ebx
> je .L4
> movzbl first_one(%eax), %ecx
> .L4:
> popl %ebx
> movl %ecx, %eax
> ret
>
>
> Here is what Intel's compiler generates:
>
> movzwl 10(%esp), %edx #28.5
> xorl %eax, %eax #30.3
> orl %edx, %eax #30.3
> je ..B1.3 # Prob 50% #30.3
> # LOE edx ebx ebp esi edi
> ..B1.2: # Preds ..B1.1
> movzbl first_one(%edx), %eax #31.13
> ret #31.13
> # LOE
> ..B1.3: # Preds ..B1.1
> xorl %eax, %eax #32.10
> ret #32.10
>
>
>
$ cc1 -quiet -m32 -O2 t.c -fdump-tree-optimized
$ cat t.s
.file "t.c"
.text
.p2align 4,,15
.globl FirstOnet
.type FirstOnet, @function
FirstOnet:
.LFB0:
.cfi_startproc
movzwl 10(%esp), %edx
xorl %eax, %eax
testl %edx, %edx
je .L2
movzbl first_one(%edx), %eax
.L2:
rep
ret
.cfi_endproc
.LFE0:
.size FirstOnet, .-FirstOnet
.ident "GCC: (GNU) 4.6.0 20110312 (experimental) [trunk revision
170907]"
.section .note.GNU-stack,"",@progbits
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug rtl-optimization/16541] code quality issue for bit manipulations with 64bit
2004-07-14 16:17 [Bug middle-end/16541] New: code quality issue for bit manipulations dann at godzilla dot ics dot uci dot edu
` (2 preceding siblings ...)
2004-08-31 17:22 ` dann at godzilla dot ics dot uci dot edu
@ 2005-05-12 17:40 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2005-05-12 17:40 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2005-05-12 17:40 -------
Looks like a register allocation issue.
--
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |ra
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16541
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug rtl-optimization/16541] code quality issue for bit manipulations with 64bit
2004-07-14 16:17 [Bug middle-end/16541] New: code quality issue for bit manipulations dann at godzilla dot ics dot uci dot edu
2004-07-14 16:28 ` [Bug rtl-optimization/16541] code quality issue for bit manipulations with 64bit pinskia at gcc dot gnu dot org
2004-07-14 21:58 ` dann at godzilla dot ics dot uci dot edu
@ 2004-08-31 17:22 ` dann at godzilla dot ics dot uci dot edu
2005-05-12 17:40 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 6+ messages in thread
From: dann at godzilla dot ics dot uci dot edu @ 2004-08-31 17:22 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From dann at godzilla dot ics dot uci dot edu 2004-08-31 17:22 -------
Using -fno-if-conversion when compiling to the code in comment #2 improves the
generated assembly a bit:
movl 8(%esp), %edx
movl %edx, %eax
xorl %edx, %edx
shrl $16, %eax
movl %edx, %ecx
orl %eax, %ecx
jne .L2
xorl %eax, %eax
ret
.p2align 4,,7
.L2:
movzbl first_one(%eax), %eax
ret
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16541
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug rtl-optimization/16541] code quality issue for bit manipulations with 64bit
2004-07-14 16:17 [Bug middle-end/16541] New: code quality issue for bit manipulations dann at godzilla dot ics dot uci dot edu
2004-07-14 16:28 ` [Bug rtl-optimization/16541] code quality issue for bit manipulations with 64bit pinskia at gcc dot gnu dot org
@ 2004-07-14 21:58 ` dann at godzilla dot ics dot uci dot edu
2004-08-31 17:22 ` dann at godzilla dot ics dot uci dot edu
2005-05-12 17:40 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 6+ messages in thread
From: dann at godzilla dot ics dot uci dot edu @ 2004-07-14 21:58 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From dann at godzilla dot ics dot uci dot edu 2004-07-14 21:58 -------
Here is a simplified test case that shows a code quality regression:
extern unsigned char first_one[65536];
int FirstOnet(unsigned long long arg1)
{
if (arg1 >> 48)
return (first_one[arg1 >> 48]);
return 0;
}
the code generated by gcc-3.0 -O2 -fomit-frame-pointer is:
movl 8(%esp), %edx
movl %edx, %eax
shrl $16, %eax
xorl %edx, %edx
movl %eax, %ecx
orl %edx, %ecx
je .L3
movzbl first_one(%eax), %eax
ret
.p2align 2
.L3:
xorl %eax, %eax
ret
and by mainline (a bit worse):
pushl %ebx <- using a callee saved register
xorl %ecx, %ecx
movl 12(%esp), %edx
movl %edx, %eax <- why not load directly to eax?
xorl %edx, %edx
shrl $16, %eax
movl %edx, %ebx
orl %eax, %ebx
je .L4
movzbl first_one(%eax), %ecx
.L4:
popl %ebx
movl %ecx, %eax
ret
Here is what Intel's compiler generates:
movzwl 10(%esp), %edx #28.5
xorl %eax, %eax #30.3
orl %edx, %eax #30.3
je ..B1.3 # Prob 50% #30.3
# LOE edx ebx ebp esi edi
..B1.2: # Preds ..B1.1
movzbl first_one(%edx), %eax #31.13
ret #31.13
# LOE
..B1.3: # Preds ..B1.1
xorl %eax, %eax #32.10
ret #32.10
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16541
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug rtl-optimization/16541] code quality issue for bit manipulations with 64bit
2004-07-14 16:17 [Bug middle-end/16541] New: code quality issue for bit manipulations dann at godzilla dot ics dot uci dot edu
@ 2004-07-14 16:28 ` pinskia at gcc dot gnu dot org
2004-07-14 21:58 ` dann at godzilla dot ics dot uci dot edu
` (2 subsequent siblings)
3 siblings, 0 replies; 6+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2004-07-14 16:28 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From pinskia at gcc dot gnu dot org 2004-07-14 16:28 -------
Confirmed, basically 64bit and subregisters are not optimized that well on x86, see PR 15792 for
another example.
--
What |Removed |Added
----------------------------------------------------------------------------
BugsThisDependsOn| |15792
Severity|normal |enhancement
Status|UNCONFIRMED |NEW
Component|middle-end |rtl-optimization
Ever Confirmed| |1
GCC target triplet| |i686-pc-linux-gnu
Keywords| |missed-optimization
Last reconfirmed|0000-00-00 00:00:00 |2004-07-14 16:28:16
date| |
Summary|code quality issue for bit |code quality issue for bit
|manipulations |manipulations with 64bit
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16541
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2011-05-22 15:44 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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[not found] <bug-16541-1008@http.gcc.gnu.org/bugzilla/>
2008-09-14 4:21 ` [Bug rtl-optimization/16541] code quality issue for bit manipulations with 64bit pinskia at gcc dot gnu dot org
[not found] <bug-16541-4@http.gcc.gnu.org/bugzilla/>
2011-05-22 15:51 ` steven at gcc dot gnu.org
2004-07-14 16:17 [Bug middle-end/16541] New: code quality issue for bit manipulations dann at godzilla dot ics dot uci dot edu
2004-07-14 16:28 ` [Bug rtl-optimization/16541] code quality issue for bit manipulations with 64bit pinskia at gcc dot gnu dot org
2004-07-14 21:58 ` dann at godzilla dot ics dot uci dot edu
2004-08-31 17:22 ` dann at godzilla dot ics dot uci dot edu
2005-05-12 17:40 ` pinskia at gcc dot gnu dot org
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