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* [Bug middle-end/33187] New: Missed cmove opportunity
@ 2007-08-25 10:34 ubizjak at gmail dot com
2007-08-25 12:39 ` [Bug middle-end/33187] " ubizjak at gmail dot com
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: ubizjak at gmail dot com @ 2007-08-25 10:34 UTC (permalink / raw)
To: gcc-bugs
This testcase:
--cut-here--
double sgn (double __x) {
return __x >= 0.0 ? 1.0 : -1.0;
}
--cut here--
shold compile using -m32 -O2 -march=i686 flags into the code using cmove
instruction, but it doesn't due to interference with float-extension of SFmode
constant into DFmode. Gcc figures out that 1.0 can be loaded as SFmode
constant, float-extended to DFmode. The RTL sequence in each arm then looks
like:
--cut here--
(insn 17 16 18 4 cmov.c:2 (set (reg:SF 64)
(mem/u/c/i:SF (symbol_ref/u:SI ("*.LC2") [flags 0x2]) [3 S4 A32])) 90
{*
movsf_1} (expr_list:REG_EQUAL (const_double:SF 1.0e+0 [0x0.8p+1])
(nil)))
(insn 18 17 19 4 cmov.c:2 (set (reg:DF 58 [ D.1658 ])
(float_extend:DF (reg:SF 64))) 127 {*extendsfdf2_i387}
(expr_list:REG_DE
AD (reg:SF 64)
(expr_list:REG_EQUAL (const_double:DF 1.0e+0 [0x0.8p+1])
(nil))))
--cut here--
This effectivelly blocks ifcvt from generating conditional move in this case.
cmov instruction is generated if 1.0 and -1.0 constants are changed to (i.e.)
1.1 and -1.1, in order to disable automatic float-extend functionality:
sgn:
fldl .LC1
fldz
fldl 4(%esp)
fucomip %st(1), %st
fstp %st(0)
fldl .LC2
fcmovb %st(1), %st
fstp %st(1)
ret
This is a middle-end bug, as the problem with float-extend should be solved in
ifcvt.c
--
Summary: Missed cmove opportunity
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ubizjak at gmail dot com
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=33187
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug middle-end/33187] Missed cmove opportunity
2007-08-25 10:34 [Bug middle-end/33187] New: Missed cmove opportunity ubizjak at gmail dot com
@ 2007-08-25 12:39 ` ubizjak at gmail dot com
2007-08-25 13:25 ` rguenth at gcc dot gnu dot org
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: ubizjak at gmail dot com @ 2007-08-25 12:39 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from ubizjak at gmail dot com 2007-08-25 12:39 -------
There is a small problem in combine. It tries to combine insn 17 and 18, but:
Failed to match this instruction:
(set (reg:DF 58 [ D.1658 ])
(const_double:DF -1.0e+0 [-0x0.8p+1]))
Failed to match this instruction:
(set (reg:DF 58 [ D.1658 ])
(const_double:DF -1.0e+0 [-0x0.8p+1]))
It looks to me, that in the second case combine "over-optimizes" the combined
instruction, failing to check for:
(set (reg:DF 58 [ D.1658 ])
(float_extend:DF (mem/u/c/i:SF (symbol_ref/u:SI ("*.LC2")))))
which just happens to be valid insn for i387 and as such also appropriate for
ifcvt cmove transformation in the second ifcvt pass (after combine).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33187
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug middle-end/33187] Missed cmove opportunity
2007-08-25 10:34 [Bug middle-end/33187] New: Missed cmove opportunity ubizjak at gmail dot com
2007-08-25 12:39 ` [Bug middle-end/33187] " ubizjak at gmail dot com
@ 2007-08-25 13:25 ` rguenth at gcc dot gnu dot org
2007-08-27 20:23 ` ubizjak at gmail dot com
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2007-08-25 13:25 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from rguenth at gcc dot gnu dot org 2007-08-25 13:25 -------
Confirmed.
--
rguenth 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 |2007-08-25 13:25:44
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33187
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug middle-end/33187] Missed cmove opportunity
2007-08-25 10:34 [Bug middle-end/33187] New: Missed cmove opportunity ubizjak at gmail dot com
2007-08-25 12:39 ` [Bug middle-end/33187] " ubizjak at gmail dot com
2007-08-25 13:25 ` rguenth at gcc dot gnu dot org
@ 2007-08-27 20:23 ` ubizjak at gmail dot com
2007-09-04 10:07 ` uros at gcc dot gnu dot org
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: ubizjak at gmail dot com @ 2007-08-27 20:23 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from ubizjak at gmail dot com 2007-08-27 20:22 -------
Patch and the description of the problem at
http://gcc.gnu.org/ml/gcc-patches/2007-08/msg01880.html.
--
ubizjak at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
AssignedTo|unassigned at gcc dot gnu |ubizjak at gmail dot com
|dot org |
URL| |http://gcc.gnu.org/ml/gcc-
| |patches/2007-
| |08/msg01880.html
Status|NEW |ASSIGNED
Keywords| |patch
Last reconfirmed|2007-08-25 13:25:44 |2007-08-27 20:22:49
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33187
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug middle-end/33187] Missed cmove opportunity
2007-08-25 10:34 [Bug middle-end/33187] New: Missed cmove opportunity ubizjak at gmail dot com
` (2 preceding siblings ...)
2007-08-27 20:23 ` ubizjak at gmail dot com
@ 2007-09-04 10:07 ` uros at gcc dot gnu dot org
2007-09-04 10:10 ` ubizjak at gmail dot com
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: uros at gcc dot gnu dot org @ 2007-09-04 10:07 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from uros at gcc dot gnu dot org 2007-09-04 10:07 -------
Subject: Bug 33187
Author: uros
Date: Tue Sep 4 10:07:19 2007
New Revision: 128072
URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=128072
Log:
PR middle-end/33187
* combine.c (subst): Do not try to simplify X if it represents load
of FP constant from the constant pool via float extension.
testsuite/ChangeLog:
PR middle-end/33187
* gcc.target/i386/cmov7.c: New file.
Added:
trunk/gcc/testsuite/gcc.target/i386/cmov7.c
Modified:
trunk/gcc/ChangeLog
trunk/gcc/combine.c
trunk/gcc/testsuite/ChangeLog
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33187
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug middle-end/33187] Missed cmove opportunity
2007-08-25 10:34 [Bug middle-end/33187] New: Missed cmove opportunity ubizjak at gmail dot com
` (3 preceding siblings ...)
2007-09-04 10:07 ` uros at gcc dot gnu dot org
@ 2007-09-04 10:10 ` ubizjak at gmail dot com
2008-01-09 18:44 ` ghazi at gcc dot gnu dot org
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: ubizjak at gmail dot com @ 2007-09-04 10:10 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from ubizjak at gmail dot com 2007-09-04 10:10 -------
Fixed.
--
ubizjak at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution| |FIXED
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33187
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug middle-end/33187] Missed cmove opportunity
2007-08-25 10:34 [Bug middle-end/33187] New: Missed cmove opportunity ubizjak at gmail dot com
` (4 preceding siblings ...)
2007-09-04 10:10 ` ubizjak at gmail dot com
@ 2008-01-09 18:44 ` ghazi at gcc dot gnu dot org
2008-01-10 14:08 ` ubizjak at gmail dot com
2008-01-11 4:38 ` ghazi at gcc dot gnu dot org
7 siblings, 0 replies; 9+ messages in thread
From: ghazi at gcc dot gnu dot org @ 2008-01-09 18:44 UTC (permalink / raw)
To: gcc-bugs
------- Comment #6 from ghazi at gcc dot gnu dot org 2008-01-09 18:25 -------
Uros, the testcase (gcc.target/i386/cmov7.c) fails on x86 with -fpic/-fPIC.
Real bug, or skip with pic?
http://gcc.gnu.org/ml/gcc-testresults/2008-01/msg00366.html
--
ghazi at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ghazi at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33187
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug middle-end/33187] Missed cmove opportunity
2007-08-25 10:34 [Bug middle-end/33187] New: Missed cmove opportunity ubizjak at gmail dot com
` (5 preceding siblings ...)
2008-01-09 18:44 ` ghazi at gcc dot gnu dot org
@ 2008-01-10 14:08 ` ubizjak at gmail dot com
2008-01-11 4:38 ` ghazi at gcc dot gnu dot org
7 siblings, 0 replies; 9+ messages in thread
From: ubizjak at gmail dot com @ 2008-01-10 14:08 UTC (permalink / raw)
To: gcc-bugs
------- Comment #7 from ubizjak at gmail dot com 2008-01-10 07:01 -------
(In reply to comment #6)
> Uros, the testcase (gcc.target/i386/cmov7.c) fails on x86 with -fpic/-fPIC.
> Real bug, or skip with pic?
No, but insn RTX costs is slightly increased for -fpic. From ix86_rtx_cost():
--cut here--
case SYMBOL_REF:
if (TARGET_64BIT && !x86_64_immediate_operand (x, VOIDmode))
*total = 3;
else if (TARGET_64BIT && !x86_64_zext_immediate_operand (x, VOIDmode))
*total = 2;
else if (flag_pic && SYMBOLIC_CONST (x)
&& (!TARGET_64BIT
|| (!GET_CODE (x) != LABEL_REF
&& (GET_CODE (x) != SYMBOL_REF
|| !SYMBOL_REF_LOCAL_P (x)))))
*total = 1;
else
*total = 0;
return true;
--cut here--
Adding -mbranch-cost=5 to dg-options would remove this failure.
--
ubizjak at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
Known to fail|4.2.0 4.3.0 |4.2.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33187
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug middle-end/33187] Missed cmove opportunity
2007-08-25 10:34 [Bug middle-end/33187] New: Missed cmove opportunity ubizjak at gmail dot com
` (6 preceding siblings ...)
2008-01-10 14:08 ` ubizjak at gmail dot com
@ 2008-01-11 4:38 ` ghazi at gcc dot gnu dot org
7 siblings, 0 replies; 9+ messages in thread
From: ghazi at gcc dot gnu dot org @ 2008-01-11 4:38 UTC (permalink / raw)
To: gcc-bugs
------- Comment #8 from ghazi at gcc dot gnu dot org 2008-01-11 03:58 -------
Thanks Uros, patch posted here:
http://gcc.gnu.org/ml/gcc-patches/2008-01/msg00445.html
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33187
^ permalink raw reply [flat|nested] 9+ messages in thread
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2007-08-25 10:34 [Bug middle-end/33187] New: Missed cmove opportunity ubizjak at gmail dot com
2007-08-25 12:39 ` [Bug middle-end/33187] " ubizjak at gmail dot com
2007-08-25 13:25 ` rguenth at gcc dot gnu dot org
2007-08-27 20:23 ` ubizjak at gmail dot com
2007-09-04 10:07 ` uros at gcc dot gnu dot org
2007-09-04 10:10 ` ubizjak at gmail dot com
2008-01-09 18:44 ` ghazi at gcc dot gnu dot org
2008-01-10 14:08 ` ubizjak at gmail dot com
2008-01-11 4:38 ` ghazi at gcc dot gnu dot org
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