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* [Bug c/31531] New: A microoptimization of isnegative or greaterthan2millions.
@ 2007-04-10 18:05 JCPiza at gmail dot com
2007-04-10 18:14 ` [Bug c/31531] " JCPiza at gmail dot com
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: JCPiza at gmail dot com @ 2007-04-10 18:05 UTC (permalink / raw)
To: gcc-bugs
/* Given X an unsigned of 32 bits, and Y a bool. Try to translate optimizing
*
* Y = X > 2147483647; to Y = ((signed)X) < 0;
* Y = X >= 2147483648; to Y = ((signed)X) < 0;
*
* [ Another optimization is to Y = (X >> 31) ]
*
* The opposite (ELSE):
*
* Y = X <= 2147483647; to Y = ((signed)X) >= 0;
* Y = X < 2147483648; to Y = ((signed)X) >= 0;
*
* [ Another optimization is to Y = ((~X) >> 31) ]
*
* 2147483647=0x7FFFFFFF 2147483648=0x80000000
*
* The unsigned comparison is become to signed comparison.
*
* by J.C. Pizarro */
# gcc version 4.1.3 20070326 (prerelease)
Full test of isnegative is PASSED.
notl %eax
shrl $31, %eax
xorl $1, %eax
IS WORSE THAN
shrl $31, %eax
---------------------
xorl %eax, %eax
cmpl $0, 4(%esp)
sets %al
IS WORSE THAN
movl 4(%esp), %eax
shrl $31, %eax
------------------------------------------------------------------------------
Full info with src code and tarball is in
http://gcc.gnu.org/ml/gcc/2007-04/msg00317.html
I'm sorry, i did want to say 2 billions, not 2 millions.
J.C. Pizarro
--
Summary: A microoptimization of isnegative or
greaterthan2millions.
Product: gcc
Version: 4.1.3
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: JCPiza at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31531
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c/31531] A microoptimization of isnegative or greaterthan2millions.
2007-04-10 18:05 [Bug c/31531] New: A microoptimization of isnegative or greaterthan2millions JCPiza at gmail dot com
@ 2007-04-10 18:14 ` JCPiza at gmail dot com
2007-04-10 18:17 ` [Bug middle-end/31531] A microoptimization of isnegative of signed integer pinskia at gcc dot gnu dot org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: JCPiza at gmail dot com @ 2007-04-10 18:14 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from JCPiza at gmail dot com 2007-04-10 19:14 -------
Created an attachment (id=13349)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=13349&action=view)
isnegative, a wonderful test of equivalence for uoptimization
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31531
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/31531] A microoptimization of isnegative of signed integer
2007-04-10 18:05 [Bug c/31531] New: A microoptimization of isnegative or greaterthan2millions JCPiza at gmail dot com
2007-04-10 18:14 ` [Bug c/31531] " JCPiza at gmail dot com
@ 2007-04-10 18:17 ` pinskia at gcc dot gnu dot org
2007-04-10 18:20 ` pinskia at gcc dot gnu dot org
2007-04-15 5:43 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2007-04-10 18:17 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from pinskia at gcc dot gnu dot org 2007-04-10 19:17 -------
What the real issue is that we don't fold !(x >= 0) into x < 0 before
expanding.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|c |middle-end
Keywords| |missed-optimization
Summary|A microoptimization of |A microoptimization of
|isnegative or |isnegative of signed integer
|greaterthan2millions. |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31531
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/31531] A microoptimization of isnegative of signed integer
2007-04-10 18:05 [Bug c/31531] New: A microoptimization of isnegative or greaterthan2millions JCPiza at gmail dot com
2007-04-10 18:14 ` [Bug c/31531] " JCPiza at gmail dot com
2007-04-10 18:17 ` [Bug middle-end/31531] A microoptimization of isnegative of signed integer pinskia at gcc dot gnu dot org
@ 2007-04-10 18:20 ` pinskia at gcc dot gnu dot org
2007-04-15 5:43 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2007-04-10 18:20 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from pinskia at gcc dot gnu dot org 2007-04-10 19:20 -------
A quick patch like:
Index: expr.c
===================================================================
--- expr.c (revision 123691)
+++ expr.c (working copy)
@@ -6828,7 +6828,7 @@
tree type;
int unsignedp;
enum machine_mode mode;
- enum tree_code code = TREE_CODE (exp);
+ enum tree_code code;
optab this_optab;
rtx subtarget, original_target;
int ignore;
@@ -6840,6 +6840,9 @@
type) \
: (expr))
+ if (TREE_CODE (exp) != COND_EXPR && !GIMPLE_TUPLE_P (exp))
+ exp = fold (exp);
+ code = TREE_CODE(exp);
if (GIMPLE_STMT_P (exp))
{
type = void_type_node;
Makes all functions emit the same code.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31531
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug middle-end/31531] A microoptimization of isnegative of signed integer
2007-04-10 18:05 [Bug c/31531] New: A microoptimization of isnegative or greaterthan2millions JCPiza at gmail dot com
` (2 preceding siblings ...)
2007-04-10 18:20 ` pinskia at gcc dot gnu dot org
@ 2007-04-15 5:43 ` pinskia at gcc dot gnu dot org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2007-04-15 5:43 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from pinskia at gcc dot gnu dot org 2007-04-15 06:43 -------
There are a couple of ways of fixing this bug, folding while going out of ssa.
Doing a tree combined which is PR 15459. Or the patch which I attached.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
BugsThisDependsOn| |15459
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2007-04-15 06:43:24
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31531
^ permalink raw reply [flat|nested] 5+ messages in thread
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2007-04-10 18:05 [Bug c/31531] New: A microoptimization of isnegative or greaterthan2millions JCPiza at gmail dot com
2007-04-10 18:14 ` [Bug c/31531] " JCPiza at gmail dot com
2007-04-10 18:17 ` [Bug middle-end/31531] A microoptimization of isnegative of signed integer pinskia at gcc dot gnu dot org
2007-04-10 18:20 ` pinskia at gcc dot gnu dot org
2007-04-15 5:43 ` pinskia at gcc dot gnu dot org
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