[Bug c++/17315] New: Strange compile-time regression either in cpp or libstdc++ against gcc3.4.1

[Bug c++/17315] New: Strange compile-time regression either in cpp or libstdc++ against gcc3.4.1

[kgardas at objectsecurity dot com]

Hello,

while trying to submit bugreport about regression in compile-time, I've found
interesting fact, that while not-preprocessed file regress on every optimization
level about 10, 20 and 30% (for -O0, 1, 2) in comparison with 3.4.1, I'm not
able to duplicate such regression while using preprocessed file. A comparison
table looks:

Not preprocessed file:
File            341-O0  350-O0  Delta%  341-O1  350-O1  Delta%  341-O2  350-O2 
Delta%
basic_seq.cc    3.77    4.21    -10.45  3.98    4.99    -20.24  3.82    5.72   
-33.22

File preprocessed by GCC 3.4.1:
File            341-O0  350-O0  Delta%  341-O1  350-O1  Delta%  341-O2  350-O2 
Delta%
basic_seq.cc    3.69    3.31    11.48   3.91    3.47    12.68   3.78    3.65    3.56

File preprocessed by GCC 3.5.0:
File            341-O0  350-O0  Delta%  341-O1  350-O1  Delta%  341-O2  350-O2 
Delta%
basic_seq.cc    4.61    4.15    11.08   5.28    4.83    9.32    5.62    5.57    0.9

3.5.0 is from 20040830.

Whole report to gcc@ mailing list can be found
here:http://gcc.gnu.org/ml/gcc/2004-09/msg00100.html

I will attach all needed file here too.

Karel

-- 
           Summary: Strange compile-time regression either in cpp or
                    libstdc++ against gcc3.4.1
           Product: gcc
           Version: 3.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kgardas at objectsecurity dot com
                CC: gcc-bugs at gcc dot gnu dot org
 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=17315

[Bug c++/17315] Strange compile-time regression either in cpp or libstdc++ against gcc3.4.1

[kgardas at objectsecurity dot com]

------- Additional Comments From kgardas at objectsecurity dot com  2004-09-04 07:29 -------
Created an attachment (id=7043)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=7043&action=view)
File basic_seq.cc preprocessed by GCC 3.5.0


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug c++/17315] Strange compile-time regression either in cpp or libstdc++ against gcc3.4.1

[kgardas at objectsecurity dot com]

------- Additional Comments From kgardas at objectsecurity dot com  2004-09-04 07:29 -------
Created an attachment (id=7042)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=7042&action=view)
File basic_seq.cc preprocessed by GCC 3.4.1


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug c++/17315] Strange compile-time regression either in cpp or libstdc++ against gcc3.4.1

[kgardas at objectsecurity dot com]

------- Additional Comments From kgardas at objectsecurity dot com  2004-09-04 07:32 -------
Created an attachment (id=7044)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=7044&action=view)
Not preprocessed basic_seq.cc file

This file is intended for comparison with both preproceesed files, to find out
what's going wrong with this issue, i.e. why 3.5.0 is faster on all
optimization levels while compiling preprocessed files in comparison with 3.4.1
and why it is slower for compiling not-preprocessed file on all optimization
levels.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression either in cpp or libstdc++ against gcc3.4.1

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |libstdc++


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression either in cpp or libstdc++ against gcc3.4.1

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-09-07 09:57 -------
Karel,

To fully reproduce this, we need all the header files needed to preprocess 
basic_seq.cc ourselves. Would you please attacch them?

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |giovannibajo at libero dot
                   |                            |it


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression either in cpp or libstdc++ against gcc3.4.1

[kgardas at objectsecurity dot com]

------- Additional Comments From kgardas at objectsecurity dot com  2004-09-07 10:21 -------
Subject: Re:  Strange compile-time regression either in
 cpp or libstdc++ against gcc3.4.1


Sure! They are attached.

Karel

------- Additional Comments From kgardas at objectsecurity dot com  2004-09-07 10:21 -------
Created an attachment (id=7062)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=7062&action=view)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug preprocessor/17315] Strange compile-time regression in cpp against gcc3.4.1

[pcarlini at suse dot de]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|libstdc++                   |preprocessor
            Summary|Strange compile-time        |Strange compile-time
                   |regression either in cpp or |regression in cpp against
                   |libstdc++ against gcc3.4.1  |gcc3.4.1


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug preprocessor/17315] Strange compile-time regression in cpp against gcc3.4.1

[kgardas at objectsecurity dot com]

------- Additional Comments From kgardas at objectsecurity dot com  2004-09-07 14:32 -------
Subject: Re:  Strange compile-time regression in cpp
 against gcc3.4.1


Paolo,

I would just like to ask if you are really sure that this is preprocessor
related and so changing component from libstdc++ to preprocessor is right,
especially when I simply preprocess files by -E and measure the same time
spent by 3.4.1 and 3.5.0 preprocessors... (0.26 second spent by 3.4.1 and
0.27 spent by 3.5.0)

Thanks,
Karel




-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug preprocessor/17315] Strange compile-time regression in cpp against gcc3.4.1

[pcarlini at suse dot de]

------- Additional Comments From pcarlini at suse dot de  2004-09-07 14:43 -------
Subject: Re:  Strange compile-time regression in cpp against gcc3.4.1

Of course libstdc++ cannot have anything to do with a compile-time
regression since it is *not* used at all!



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug preprocessor/17315] Strange compile-time regression in cpp against gcc3.4.1

[pcarlini at suse dot de]

------- Additional Comments From pcarlini at suse dot de  2004-09-07 15:00 -------
To be clear: libstdc++ is a *runtime* library, not a part of the compiler 
proper (like libcpp, for instance). Of course C++ applications eventually link 
it and of course the library may grow bigger and the link itself can become 
slower. But definitely this cannot be considered a library bug: the libstdc++ 
category is for bugs of the library proper. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug preprocessor/17315] Strange compile-time regression in cpp against gcc3.4.1

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-09-07 15:03 -------
Paolo,

I don't understand. libstdc++ headers are brought in by #include directives. It 
looks like in 3.5 more stuff is included, and the difference results in 10% of 
compile-time difference.

Now, when the file is already preprocessed, CPP really has to do nothing but 
tokenize the stream. I do not understand why you think this to be a CPP bug. 
Would you care explaining?

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug preprocessor/17315] Strange compile-time regression in cpp against gcc3.4.1

[kgardas at objectsecurity dot com]

------- Additional Comments From kgardas at objectsecurity dot com  2004-09-07 15:08 -------
Subject: Re:  Strange compile-time regression in cpp
 against gcc3.4.1


Paolo,

thanks for your explanation, but I see possible way how libstdc++ may
affect c++ compile-time performance, the way is that it may use much
complicated macros evaluation and so hitting cpp performance, not talking
about the fact that include files might be just bigger. The problem is
that when testing cpp performance separately, I see nearly the same
results, so certainly both preprocessor are good and speedy in saving ii
files. My guess is that the problem migt be somewhere between 3.5.0's cpp
and cc1plus, i.e. data transfer, but not knowing anything about gcc's
internals this is just wild guess...

Karel




-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug preprocessor/17315] Strange compile-time regression in cpp against gcc3.4.1

[pcarlini at suse dot de]

------- Additional Comments From pcarlini at suse dot de  2004-09-07 15:09 -------
I have no idea whether cpp is involved or not... Probably it's not, as you are 
saying. I have only removed the wrong categorization libstdc++ which is 
certainly wrong, since it's used for bugs in the library. Please notice that I 
have *not* confirmed the bug! 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug preprocessor/17315] Strange compile-time regression in cpp against gcc3.4.1

[kgardas at objectsecurity dot com]

------- Additional Comments From kgardas at objectsecurity dot com  2004-09-07 15:11 -------
Subject: Re:  Strange compile-time regression in cpp
 against gcc3.4.1


Giovanni,

I'm afraid Paolo is right that this is not libstdc++ bug, especially when
-E comparison are nearly the same and difference in line numbers count of
preprocessed files is just minor:

$ ~/usr/local/gcc3.4.2/bin/c++ -time -I../include  -time -O0 -Wall   -DPIC -fPIC  -E basic_seq.cc|wc -l
# cc1plus 0.25 0.03
  46477
$ c++ -time -I../include  -time -O0 -Wall   -DPIC -fPIC  -E basic_seq.cc|wc -l
# cc1plus 0.27 0.03
  47680
$

Karel



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug preprocessor/17315] Strange compile-time regression in cpp against gcc3.4.1

[giovannibajo at libero dot it]

------- Additional Comments From giovannibajo at libero dot it  2004-09-08 00:19 -------
Subject: Re:  Strange compile-time regression in cpp against gcc3.4.1

pcarlini at suse dot de wrote:

> I have no idea whether cpp is involved or not...

It is not, because it can be reproduced with .ii files, where the preprocessed
is not even invoked.

>  it's not, as you are saying. I have only removed the wrong
> categorization libstdc++ which is
> certainly wrong, since it's used for bugs in the library. Please
> notice that I have *not* confirmed the bug!

The *only* difference between the two preprocessed files is libstdc++.

Let's say for a moment that, for some absurd reason, including <iostream> in
3.5 brings into scope 4000 new instantiations that where not present in 3.4.
This would cause a compile-time regression for any program including iostream.
How would you mark such a bug, if not with libstdc++?

There is only one data point in this bug: including libstdc++ from 3.5 causes
*at least* 10% compile-time regression compared to libstdc++ from 3.4. Now,
either the new libstdc++ exploits by mere chance some special bottleneck in the
compiler while the old libstdc++ didn't, or the code itself is slower to
compile for some reason. This is kind of hard to analyze and surely an
interesting issue (the regression is enough to totally destroy the compile-time
improvements that the tree-ssa folks brought to us), so I would appreciate some
help, and not only something like "please this is not my bug, go away".

Giovanni Bajo




-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression in cpp against gcc3.4.1

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-09-08 05:35 -------
As shown the preprocessed file has got faster with 3.5.0 so it cannot be cpp at all.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|preprocessor                |libstdc++


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression in cpp against gcc3.4.1

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-09-08 05:37 -------
I should also note the numbers come with repsect with 3.5.0 preprocessed source and 3.4.0 
preprocessed source on both compilers so we see that 3.5.0 is faster on both preprocessed source so 
even the C++ front-end is slower.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug c++/17315] Strange compile-time regression in cpp against gcc3.4.1

[pcarlini at suse dot de]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|libstdc++                   |c++


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression in cpp against gcc3.4.1

[pcarlini at suse dot de]

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------- Additional Comments From pcarlini at suse dot de  2004-09-08 09:13 -------
IMO the comparison itself doesn´t make much sense, since current mainline is 
using mt_allocator by default, while 3.4.1 uses the new-based allocator: FWIW, 
this difference explains the increased size of the pre-processed source but in 
general compiling and linking a testcase preprocessed with 3.4.1 with current 
mainline doesn´t make much sense... 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |libstdc++


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression in cpp against gcc3.4.1

[giovannibajo at libero dot it]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 1103 bytes --]


------- Additional Comments From giovannibajo at libero dot it  2004-09-08 11:13 -------
Subject: Re:  Strange compile-time regression in cpp against gcc3.4.1

pcarlini at suse dot de wrote:

> IMO the comparison itself doesn´t make much sense,
> since current mainline is using mt_allocator by default, while 3.4.1
> uses the new-based allocator: FWIW, this difference explains the
> increased size of the pre-processed source but in general compiling
> and linking a testcase preprocessed with 3.4.1 with current mainline
> doesn´t make much sense...

Well, it would not if the compiler behaved almost the same, as I would have
expected. A 10% difference means that either the mt_allocator is too slow to be
compiled for some reason, or that the frontend is too slow on it and it should
not.

Is there a way to set the new-based allocator as default in 3.5? Even a
temporary patch Karel can try. If switching back to the new-based allocator in
3.5.0 gets the performance back, at least we would have isolated the problem.

Giovanni Bajo




-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression in cpp against gcc3.4.1

[pcarlini at suse dot de]

------- Additional Comments From pcarlini at suse dot de  2004-09-08 11:38 -------
Yes, Giovanni, I agree that this kind of test is worth doing. Just passing 
--enable-libstdcxx-allocator=new at configure time suffices. The viceversa 
would be also useful, that is, passing --enable-libstdcxx-allocator=mt to 
3.4.1 configure. However, again, please remember that the user, in general, is 
*not* supposed to preprocess with 3.4.1 and compile/link with 3.5.0 (or much 
more generally, use an allocator type at pre-processing time and a different 
one at compile/link time), *very* bad things can happen... ;) 
Also, please consider that mt_allocator is more complex and *is* expected to 
be more challenging for the compiler: its performance are *much* better, no 
free lunch... ;) 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression in cpp against gcc3.4.1

[kgardas at objectsecurity dot com]

------- Additional Comments From kgardas at objectsecurity dot com  2004-09-09 20:07 -------
Subject: Re:  Strange compile-time regression in cpp
 against gcc3.4.1


As Paolo suggested, I have tried to use new based allocator and configure
gcc with --enable-libstdcxx-allocator=new.

Results are:

File		341-O0	350-O0	Delta%	341-O1	350-O1	Delta%	341-O2	350-O2	Delta%
basic_seq.cc	3.78	3.60	5.0	4.01	3.76	6.6	3.92	4.01	-2.2


which looks like --enable-libstdcxx-allocator=new is a good candidate for
a fast C++ compilations. :-) I hope I will be able to test it on a full
orb directory to see all results.

Cheers,
Karel



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression in cpp against gcc3.4.1

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-12-08 00:12 -------
So can we close this as not to be fixed as it is new allocator which is causing the problem (which is 
runtime improvement)?

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression in cpp against gcc3.4.1

[pcarlini at suse dot de]

------- Additional Comments From pcarlini at suse dot de  2004-12-08 10:23 -------
Yes, Andrew, we cannot do anything about this.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression in cpp against gcc3.4.1

[kgardas at objectsecurity dot com]

------- Additional Comments From kgardas at objectsecurity dot com  2004-12-08 10:26 -------
Subject: Re:  Strange compile-time regression in cpp
 against gcc3.4.1


Sure, close it! 4.0.0 is enough faster anyway! :-)

Cheers,
Karel



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315

[Bug libstdc++/17315] Strange compile-time regression in cpp against gcc3.4.1

[pcarlini at suse dot de]

------- Additional Comments From pcarlini at suse dot de  2004-12-08 10:31 -------
Ok ;)

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17315