public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug target/40603] unnecessary conversion from unsigned byte load to signed byte load
2009-07-01 6:56 [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load carrot at google dot com
@ 2009-07-01 6:56 ` carrot at google dot com
2009-07-01 9:13 ` ramana dot radhakrishnan at arm dot com
` (8 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: carrot at google dot com @ 2009-07-01 6:56 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from carrot at google dot com 2009-07-01 06:56 -------
Created an attachment (id=18105)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18105&action=view)
test case
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40603
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load
@ 2009-07-01 6:56 carrot at google dot com
2009-07-01 6:56 ` [Bug target/40603] " carrot at google dot com
` (9 more replies)
0 siblings, 10 replies; 11+ messages in thread
From: carrot at google dot com @ 2009-07-01 6:56 UTC (permalink / raw)
To: gcc-bugs
Compile the following function with options -Os -mthumb -march=armv5te
int ldrb(unsigned char* p)
{
if (p[8] <= 0x7F)
return 2;
else
return 5;
}
Gcc generates following codes:
push {lr}
mov r3, #8
ldrsb r3, [r0, r3]
mov r0, #2
cmp r3, #0
bge .L2
mov r0, #5
.L2:
@ sp needed for prologue
pop {pc}
The source code if (p[8] <= 0x7F) is translated to:
mov r3, #8
ldrsb r3, [r0, r3]
cmp r3, #0
A better code sequence should be:
ldrb r3, [r0, 8]
cmp r3, 0x7F
This can save one instruction.
The tree dump shows in a very early pass (ldrb.c.003t.original) the comparison
was transformed to
if ((signed char) *(p + 8) >= 0)
I guess gcc thinks comparing with 0 is much cheaper than comparing with other
numbers. Am I right?
Unfortunately in thumb mode, loading a signed byte costs more than loading an
unsigned byte and comparing with 0 has same cost as comparing with 0x7F.
--
Summary: unnecessary conversion from unsigned byte load to signed
byte load
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: carrot at google dot com
GCC build triplet: i686-linux
GCC host triplet: i686-linux
GCC target triplet: arm-eabi
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40603
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug target/40603] unnecessary conversion from unsigned byte load to signed byte load
2009-07-01 6:56 [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load carrot at google dot com
2009-07-01 6:56 ` [Bug target/40603] " carrot at google dot com
@ 2009-07-01 9:13 ` ramana dot radhakrishnan at arm dot com
2009-07-01 9:13 ` [Bug target/40603] New: " Ramana Radhakrishnan
` (7 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: ramana dot radhakrishnan at arm dot com @ 2009-07-01 9:13 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from ramana dot radhakrishnan at arm dot com 2009-07-01 09:13 -------
Subject: Re: New: unnecessary conversion from unsigned
byte load to signed byte load
> Unfortunately in thumb mode, loading a signed byte costs more than loading an
> unsigned byte and comparing with 0 has same cost as comparing with 0x7F.
I don't know of any core where loading a signed byte is more expensive
than unsigned byte in thumb mode. What did you have in mind ?
I suspect what you mean is that the sign extension here is not required
and we could get away with ldrb.
>
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40603
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load
2009-07-01 6:56 [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load carrot at google dot com
2009-07-01 6:56 ` [Bug target/40603] " carrot at google dot com
2009-07-01 9:13 ` ramana dot radhakrishnan at arm dot com
@ 2009-07-01 9:13 ` Ramana Radhakrishnan
2009-07-01 10:25 ` [Bug target/40603] " carrot at google dot com
` (6 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: Ramana Radhakrishnan @ 2009-07-01 9:13 UTC (permalink / raw)
To: gcc-bugzilla; +Cc: gcc-bugs
> Unfortunately in thumb mode, loading a signed byte costs more than loading an
> unsigned byte and comparing with 0 has same cost as comparing with 0x7F.
I don't know of any core where loading a signed byte is more expensive
than unsigned byte in thumb mode. What did you have in mind ?
I suspect what you mean is that the sign extension here is not required
and we could get away with ldrb.
>
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug target/40603] unnecessary conversion from unsigned byte load to signed byte load
2009-07-01 6:56 [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load carrot at google dot com
` (2 preceding siblings ...)
2009-07-01 9:13 ` [Bug target/40603] New: " Ramana Radhakrishnan
@ 2009-07-01 10:25 ` carrot at google dot com
2009-07-08 10:50 ` ramana at gcc dot gnu dot org
` (5 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: carrot at google dot com @ 2009-07-01 10:25 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from carrot at google dot com 2009-07-01 10:24 -------
(In reply to comment #2)
> Subject: Re: New: unnecessary conversion from unsigned
> byte load to signed byte load
>
>
> > Unfortunately in thumb mode, loading a signed byte costs more than loading an
> > unsigned byte and comparing with 0 has same cost as comparing with 0x7F.
>
> I don't know of any core where loading a signed byte is more expensive
> than unsigned byte in thumb mode. What did you have in mind ?
>
> I suspect what you mean is that the sign extension here is not required
> and we could get away with ldrb.
>
In thumb1, instruction ldrb has an addressing mode of Rn + imm5, but ldrsb has
only addressing mode of Rn + Rm. So loading unsigned byte from p[8] needs only
one instruction
ldrb r3, [r0, 8]
But loading singed byte from p[8] needs two instructions:
mov r3, 8
ldrsb r3, [r0, r3]
So in this case (base + constant offset), loading a signed byte is more
expensive than unsigned byte in thumb mode.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40603
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug target/40603] unnecessary conversion from unsigned byte load to signed byte load
2009-07-01 6:56 [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load carrot at google dot com
` (3 preceding siblings ...)
2009-07-01 10:25 ` [Bug target/40603] " carrot at google dot com
@ 2009-07-08 10:50 ` ramana at gcc dot gnu dot org
2009-07-22 21:22 ` rearnsha at gcc dot gnu dot org
` (4 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: ramana at gcc dot gnu dot org @ 2009-07-08 10:50 UTC (permalink / raw)
To: gcc-bugs
--
ramana at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2009-07-08 10:49:52
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40603
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug target/40603] unnecessary conversion from unsigned byte load to signed byte load
2009-07-01 6:56 [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load carrot at google dot com
` (4 preceding siblings ...)
2009-07-08 10:50 ` ramana at gcc dot gnu dot org
@ 2009-07-22 21:22 ` rearnsha at gcc dot gnu dot org
2010-03-20 19:29 ` ramana at gcc dot gnu dot org
` (3 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: rearnsha at gcc dot gnu dot org @ 2009-07-22 21:22 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from rearnsha at gcc dot gnu dot org 2009-07-22 21:22 -------
The transformation to signed char is done very early on (maybe even during
parsing). The 003t.original dump already contains:
if ((signed char) *(p + 8) >= 0)
--
rearnsha at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rearnsha at gcc dot gnu dot
| |org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40603
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug target/40603] unnecessary conversion from unsigned byte load to signed byte load
2009-07-01 6:56 [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load carrot at google dot com
` (5 preceding siblings ...)
2009-07-22 21:22 ` rearnsha at gcc dot gnu dot org
@ 2010-03-20 19:29 ` ramana at gcc dot gnu dot org
2010-03-26 12:01 ` bernds at codesourcery dot com
` (2 subsequent siblings)
9 siblings, 0 replies; 11+ messages in thread
From: ramana at gcc dot gnu dot org @ 2010-03-20 19:29 UTC (permalink / raw)
To: gcc-bugs
--
ramana at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
Keywords| |missed-optimization
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40603
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug target/40603] unnecessary conversion from unsigned byte load to signed byte load
2009-07-01 6:56 [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load carrot at google dot com
` (6 preceding siblings ...)
2010-03-20 19:29 ` ramana at gcc dot gnu dot org
@ 2010-03-26 12:01 ` bernds at codesourcery dot com
2010-04-16 10:05 ` bernds at gcc dot gnu dot org
2010-04-16 11:23 ` bernds at gcc dot gnu dot org
9 siblings, 0 replies; 11+ messages in thread
From: bernds at codesourcery dot com @ 2010-03-26 12:01 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from bernds at codesourcery dot com 2010-03-26 12:01 -------
http://gcc.gnu.org/ml/gcc-patches/2010-03/msg01235.html
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40603
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug target/40603] unnecessary conversion from unsigned byte load to signed byte load
2009-07-01 6:56 [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load carrot at google dot com
` (7 preceding siblings ...)
2010-03-26 12:01 ` bernds at codesourcery dot com
@ 2010-04-16 10:05 ` bernds at gcc dot gnu dot org
2010-04-16 11:23 ` bernds at gcc dot gnu dot org
9 siblings, 0 replies; 11+ messages in thread
From: bernds at gcc dot gnu dot org @ 2010-04-16 10:05 UTC (permalink / raw)
To: gcc-bugs
------- Comment #6 from bernds at gcc dot gnu dot org 2010-04-16 10:05 -------
Subject: Bug 40603
Author: bernds
Date: Fri Apr 16 10:04:15 2010
New Revision: 158407
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=158407
Log:
PR target/40603
* config/arm/arm.md (cbranchqi4): New pattern.
* config/arm/predicates.md (const0_operand,
cbranchqi4_comparison_operator): New predicates.
PR target/40603
* gcc.target/arm/thumb-cbranchqi.c: New test.
Added:
trunk/gcc/testsuite/gcc.target/arm/thumb-cbranchqi.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/config/arm/arm.md
trunk/gcc/config/arm/predicates.md
trunk/gcc/testsuite/ChangeLog
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40603
^ permalink raw reply [flat|nested] 11+ messages in thread
* [Bug target/40603] unnecessary conversion from unsigned byte load to signed byte load
2009-07-01 6:56 [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load carrot at google dot com
` (8 preceding siblings ...)
2010-04-16 10:05 ` bernds at gcc dot gnu dot org
@ 2010-04-16 11:23 ` bernds at gcc dot gnu dot org
9 siblings, 0 replies; 11+ messages in thread
From: bernds at gcc dot gnu dot org @ 2010-04-16 11:23 UTC (permalink / raw)
To: gcc-bugs
------- Comment #7 from bernds at gcc dot gnu dot org 2010-04-16 11:23 -------
Fixed.
--
bernds at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40603
^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2010-04-16 11:23 UTC | newest]
Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2009-07-01 6:56 [Bug target/40603] New: unnecessary conversion from unsigned byte load to signed byte load carrot at google dot com
2009-07-01 6:56 ` [Bug target/40603] " carrot at google dot com
2009-07-01 9:13 ` ramana dot radhakrishnan at arm dot com
2009-07-01 9:13 ` [Bug target/40603] New: " Ramana Radhakrishnan
2009-07-01 10:25 ` [Bug target/40603] " carrot at google dot com
2009-07-08 10:50 ` ramana at gcc dot gnu dot org
2009-07-22 21:22 ` rearnsha at gcc dot gnu dot org
2010-03-20 19:29 ` ramana at gcc dot gnu dot org
2010-03-26 12:01 ` bernds at codesourcery dot com
2010-04-16 10:05 ` bernds at gcc dot gnu dot org
2010-04-16 11:23 ` bernds at gcc dot gnu dot org
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).