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* [Bug target/29042] New: Useless floating-point stores and loads on x86
@ 2006-09-12 20:28 guillaume dot melquiond at ens-lyon dot fr
2006-10-30 2:17 ` [Bug target/29042] [4.0/4.1/4.2/4.3 Regression] " pinskia at gcc dot gnu dot org
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: guillaume dot melquiond at ens-lyon dot fr @ 2006-09-12 20:28 UTC (permalink / raw)
To: gcc-bugs
This is the same testcase as PR26778. This bug is marked as resolved, and the
patch indeed prevents GCC from using useless mmx registers. Concerning integer
operations, the generated assembly got even better than GCC 3.4, as the values
are directly incremented in memory instead of being loaded and stored; no
callee-save register is used anymore. Unfortunately, there is still a
regression with respect to the floating-point stack.
Testcase compiled with -march=pentium3 -O3:
typedef union {
long long l;
double d;
} db_number;
double test(double x[3]) {
double th = x[1] + x[2];
if (x[2] != th - x[1]) {
db_number thdb;
thdb.d = th;
thdb.l++;
th = thdb.d;
}
return x[0] + th;
}
It may be clearer with a unified diff between the assembly code generated by
3.4.6 and the one by 4.2.0 (svn 2006-09-12). Note: the assembly code for 3.4
was edited by hand in order to reduce the noise due to mismatching integer
registers.
pushl %ebp
movl %esp, %ebp
subl $16, %esp
movl 8(%ebp), %eax
fldl 8(%eax)
fldl 16(%eax)
fld %st(1)
fadd %st(1), %st
+ fstl -8(%ebp)
fsub %st, %st(2)
fxch %st(1)
fucomip %st(2), %st
fstp %st(1)
jp .L7
- je .L2
+ je .L9
.L7:
fstpl -16(%ebp)
addl $1, -16(%ebp)
adcl $0, -12(%ebp)
fldl -16(%ebp)
+ fstpl -8(%ebp)
+ jmp .L2
+ .p2align 4,,7
+.L9:
+ fstp %st(0)
+ .p2align 4,,15
.L2:
+ fldl -8(%ebp)
faddl (%eax)
leave
ret
The 3.4 code never stores the value of th; it is kept at the top of the
floating-point stack. In my opinion, this is optimal. This is no longer the
case with 4.2 code. The value of "th" is stored in -8(%ebp). Then, on one
branch (L7), it is overwritten with the content of -16(%ebp). And on the other
branch (L9), the value is discarded from the top of the stack and then
immediatly (L2) reloaded from memory. Each line prefixed by + is useless: if
none is present, the code will still behave correctly and it will contain five
assembly instructions less.
--
Summary: Useless floating-point stores and loads on x86
Product: gcc
Version: 4.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: guillaume dot melquiond at ens-lyon dot fr
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29042
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/29042] [4.0/4.1/4.2/4.3 Regression] Useless floating-point stores and loads on x86
2006-09-12 20:28 [Bug target/29042] New: Useless floating-point stores and loads on x86 guillaume dot melquiond at ens-lyon dot fr
@ 2006-10-30 2:17 ` pinskia at gcc dot gnu dot org
2006-11-01 18:23 ` mmitchel at gcc dot gnu dot org
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2006-10-30 2:17 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from pinskia at gcc dot gnu dot org 2006-10-30 02:17 -------
Confirmed, this regression was caused by the removal of ADDRESSOF.
--
pinskia 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 |2006-10-30 02:17:03
date| |
Summary|Useless floating-point |[4.0/4.1/4.2/4.3 Regression]
|stores and loads on x86 |Useless floating-point
| |stores and loads on x86
Target Milestone|--- |4.0.4
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29042
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/29042] [4.0/4.1/4.2/4.3 Regression] Useless floating-point stores and loads on x86
2006-09-12 20:28 [Bug target/29042] New: Useless floating-point stores and loads on x86 guillaume dot melquiond at ens-lyon dot fr
2006-10-30 2:17 ` [Bug target/29042] [4.0/4.1/4.2/4.3 Regression] " pinskia at gcc dot gnu dot org
@ 2006-11-01 18:23 ` mmitchel at gcc dot gnu dot org
2007-02-03 20:05 ` gdr at gcc dot gnu dot org
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: mmitchel at gcc dot gnu dot org @ 2006-11-01 18:23 UTC (permalink / raw)
To: gcc-bugs
--
mmitchel at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29042
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/29042] [4.0/4.1/4.2/4.3 Regression] Useless floating-point stores and loads on x86
2006-09-12 20:28 [Bug target/29042] New: Useless floating-point stores and loads on x86 guillaume dot melquiond at ens-lyon dot fr
2006-10-30 2:17 ` [Bug target/29042] [4.0/4.1/4.2/4.3 Regression] " pinskia at gcc dot gnu dot org
2006-11-01 18:23 ` mmitchel at gcc dot gnu dot org
@ 2007-02-03 20:05 ` gdr at gcc dot gnu dot org
2007-02-03 21:01 ` pinskia at gcc dot gnu dot org
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: gdr at gcc dot gnu dot org @ 2007-02-03 20:05 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from gdr at gcc dot gnu dot org 2007-02-03 20:05 -------
Won't fix in GCC-4.0.x. Adjusting milestone.
--
gdr at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|4.0.4 |4.1.3
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29042
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/29042] [4.0/4.1/4.2/4.3 Regression] Useless floating-point stores and loads on x86
2006-09-12 20:28 [Bug target/29042] New: Useless floating-point stores and loads on x86 guillaume dot melquiond at ens-lyon dot fr
` (2 preceding siblings ...)
2007-02-03 20:05 ` gdr at gcc dot gnu dot org
@ 2007-02-03 21:01 ` pinskia at gcc dot gnu dot org
2007-02-14 9:20 ` mmitchel at gcc dot gnu dot org
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2007-02-03 21:01 UTC (permalink / raw)
To: gcc-bugs
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|4.1.3 |4.1.2
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29042
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/29042] [4.0/4.1/4.2/4.3 Regression] Useless floating-point stores and loads on x86
2006-09-12 20:28 [Bug target/29042] New: Useless floating-point stores and loads on x86 guillaume dot melquiond at ens-lyon dot fr
` (3 preceding siblings ...)
2007-02-03 21:01 ` pinskia at gcc dot gnu dot org
@ 2007-02-14 9:20 ` mmitchel at gcc dot gnu dot org
2007-06-18 5:29 ` [Bug target/29042] [4.0/4.1/4.2 " pinskia at gcc dot gnu dot org
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: mmitchel at gcc dot gnu dot org @ 2007-02-14 9:20 UTC (permalink / raw)
To: gcc-bugs
--
mmitchel at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|4.1.2 |4.1.3
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29042
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/29042] [4.0/4.1/4.2 Regression] Useless floating-point stores and loads on x86
2006-09-12 20:28 [Bug target/29042] New: Useless floating-point stores and loads on x86 guillaume dot melquiond at ens-lyon dot fr
` (4 preceding siblings ...)
2007-02-14 9:20 ` mmitchel at gcc dot gnu dot org
@ 2007-06-18 5:29 ` pinskia at gcc dot gnu dot org
2008-07-04 21:31 ` [Bug target/29042] [4.2 " jsm28 at gcc dot gnu dot org
2009-03-30 19:37 ` jsm28 at gcc dot gnu dot org
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu dot org @ 2007-06-18 5:29 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from pinskia at gcc dot gnu dot org 2007-06-18 05:29 -------
This has now been fixed on the trunk. I think by the dataflow branch merge.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Known to work| |4.3.0
Summary|[4.0/4.1/4.2/4.3 Regression]|[4.0/4.1/4.2 Regression]
|Useless floating-point |Useless floating-point
|stores and loads on x86 |stores and loads on x86
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29042
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/29042] [4.2 Regression] Useless floating-point stores and loads on x86
2006-09-12 20:28 [Bug target/29042] New: Useless floating-point stores and loads on x86 guillaume dot melquiond at ens-lyon dot fr
` (5 preceding siblings ...)
2007-06-18 5:29 ` [Bug target/29042] [4.0/4.1/4.2 " pinskia at gcc dot gnu dot org
@ 2008-07-04 21:31 ` jsm28 at gcc dot gnu dot org
2009-03-30 19:37 ` jsm28 at gcc dot gnu dot org
7 siblings, 0 replies; 9+ messages in thread
From: jsm28 at gcc dot gnu dot org @ 2008-07-04 21:31 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from jsm28 at gcc dot gnu dot org 2008-07-04 21:31 -------
Closing 4.1 branch.
--
jsm28 at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|[4.1/4.2 Regression] Useless|[4.2 Regression] Useless
|floating-point stores and |floating-point stores and
|loads on x86 |loads on x86
Target Milestone|4.1.3 |4.2.5
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29042
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug target/29042] [4.2 Regression] Useless floating-point stores and loads on x86
2006-09-12 20:28 [Bug target/29042] New: Useless floating-point stores and loads on x86 guillaume dot melquiond at ens-lyon dot fr
` (6 preceding siblings ...)
2008-07-04 21:31 ` [Bug target/29042] [4.2 " jsm28 at gcc dot gnu dot org
@ 2009-03-30 19:37 ` jsm28 at gcc dot gnu dot org
7 siblings, 0 replies; 9+ messages in thread
From: jsm28 at gcc dot gnu dot org @ 2009-03-30 19:37 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from jsm28 at gcc dot gnu dot org 2009-03-30 19:37 -------
Closing 4.2 branch, fixed in 4.3.
--
jsm28 at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Known to fail|4.0.4 |4.0.4 4.2.5
Resolution| |FIXED
Target Milestone|4.2.5 |4.3.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29042
^ permalink raw reply [flat|nested] 9+ messages in thread
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2006-09-12 20:28 [Bug target/29042] New: Useless floating-point stores and loads on x86 guillaume dot melquiond at ens-lyon dot fr
2006-10-30 2:17 ` [Bug target/29042] [4.0/4.1/4.2/4.3 Regression] " pinskia at gcc dot gnu dot org
2006-11-01 18:23 ` mmitchel at gcc dot gnu dot org
2007-02-03 20:05 ` gdr at gcc dot gnu dot org
2007-02-03 21:01 ` pinskia at gcc dot gnu dot org
2007-02-14 9:20 ` mmitchel at gcc dot gnu dot org
2007-06-18 5:29 ` [Bug target/29042] [4.0/4.1/4.2 " pinskia at gcc dot gnu dot org
2008-07-04 21:31 ` [Bug target/29042] [4.2 " jsm28 at gcc dot gnu dot org
2009-03-30 19:37 ` jsm28 at gcc dot gnu dot org
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