[Bug math/6406] Improve performance of libm wrapper functions.

[Bug math/6406] Improve performance of libm wrapper functions.

[aj at suse dot de]

http://sourceware.org/bugzilla/show_bug.cgi?id=6406

Andreas Jaeger <aj at suse dot de> changed:

           What    |Removed                     |Added
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         AssignedTo|aj at suse dot de           |drepper.fsp at gmail dot
                   |                            |com

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[Bug math/6406] Improve performance of libm wrapper functions.

[drepper.fsp at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=6406

--- Comment #7 from Ulrich Drepper <drepper.fsp at gmail dot com> 2011-10-08 08:45:27 UTC ---
This is horrible.

Provide optimized inline versions of the standard functions and then fix the
compiler to reuse the result of function calls which convert the floating-point
numbers to the bitmasks.  If the inlined conversion function is marked 'const'
then the compiler should be able to determine that subsequent calls to


   bits = float2bits(floatvar);

return exactly the same result and should reuse it (given that floatvar hasn't
changed).

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[Bug math/6406] Improve performance of libm wrapper functions.

[jakub at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=6406

Jakub Jelinek <jakub at redhat dot com> changed:

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                 CC|                            |jakub at redhat dot com

--- Comment #8 from Jakub Jelinek <jakub at redhat dot com> 2011-10-08 09:21:01 UTC ---
For all these 4 functions has gcc its builtins, and if the gcc compiled code
using those builtins could be improved, a bug with particular testcases should
be filed against gcc.

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[Bug math/6406] Improve performance of libm wrapper functions.

[drepper.fsp at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=6406

Ulrich Drepper <drepper.fsp at gmail dot com> changed:

           What    |Removed                     |Added
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             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #9 from Ulrich Drepper <drepper.fsp at gmail dot com> 2011-10-15 14:13:59 UTC ---
I'm closing this bug.  I optimized the wrappers *correctly*.  Anything else is
up to the compiler and those people who care about the niche architectures. 
They have to provide additions to their respective math_private.h.

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[Bug math/6406] New: Improve performance of libm wrapper functions.

[sjmunroe at us dot ibm dot com]

Many math lib functions have a wrapper function in front of the ieee754
implementation. This wrapper function will check for specific error conditions
and set errno as required by C99 or Posix.

This wrapper function can add significant path length and is composed of often
redundant isnan, isinf, finite tests which is incur the call overhead to that
function. Also since we are using the general purpose functions, the same value
is  transfered and manipulated in the same or similar ways multiple times.

Performance could be improved by making these tests inline, allowing the
compiler and optimize out data transfers and common subexpressions.

-- 
           Summary: Improve performance of libm wrapper functions.
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: aj at suse dot de
        ReportedBy: sjmunroe at us dot ibm dot com
                CC: glibc-bugs at sources dot redhat dot com
GCC target triplet: powerpc64-*-linux and others


http://sourceware.org/bugzilla/show_bug.cgi?id=6406

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[Bug math/6406] Improve performance of libm wrapper functions.

[sjmunroe at us dot ibm dot com]

------- Additional Comments From sjmunroe at us dot ibm dot com  2008-04-15 02:00 -------
Created an attachment (id=2691)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=2691&action=view)
A proposed method for inlining range checks in libm wrappers

This method defines macros in math_private.h that; declare transfer variables
(unions), transfer FP parms to a convenient (int) form for manipulation, 
defines macros for inline versions of ISNAN, ISINF, FINITE, SIGNBIT. 
the the DCL and XFER macros are separate to allow the flexibility for
scheduling.
This version includes the default math/math_private.h, examples uses for
w_exp.c w_log.c and w_pow.c and a platform specific override for powerpc.

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[Bug math/6406] Improve performance of libm wrapper functions.

[sjmunroe at us dot ibm dot com]

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http://sourceware.org/bugzilla/show_bug.cgi?id=6406

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[Bug math/6406] Improve performance of libm wrapper functions.

[sjmunroe at us dot ibm dot com]

------- Additional Comments From sjmunroe at us dot ibm dot com  2008-04-15 02:16 -------
The implementation above returns a performance improvement at the micro
benchmark level of 4% (w_exp), 8% (w_log), and 15% (w_pow) for power5 and power6
systems. based on GCC-4.3 and todays GLIBC cvs.

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[Bug math/6406] Improve performance of libm wrapper functions.

[sjmunroe at us dot ibm dot com]

------- Additional Comments From sjmunroe at us dot ibm dot com  2008-04-15 02:27 -------
Created an attachment (id=2692)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=2692&action=view)
Example implementation of the x86_64 platform

This is an example for x86_64. So far it returns mixed results. the results are
disappointing for w_exp and w_log but an impressive 43% improvement for w_pow.
Not sure why the simpler w_exp and w_log case do not improve. As far as I can
tell the total path is shorter with this test patch.

This is only test and without this patch ./math/math_privated.h from the
previous patch maintains the existing implementation.

I am sure someone more skilled in x86_64 can devise a solution that retains the
gains for w_pow and resolves the problems with w_exp and w_log.

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[Bug math/6406] Improve performance of libm wrapper functions.

[sjmunroe at us dot ibm dot com]

------- Additional Comments From sjmunroe at us dot ibm dot com  2008-04-15 16:07 -------
marked the severity as enhancement

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           Severity|normal                      |enhancement


http://sourceware.org/bugzilla/show_bug.cgi?id=6406

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[Bug math/6406] Improve performance of libm wrapper functions.

[sjmunroe at us dot ibm dot com]

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http://sourceware.org/bugzilla/show_bug.cgi?id=6406

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[Bug math/6406] Improve performance of libm wrapper functions.

[sjmunroe at us dot ibm dot com]

------- Additional Comments From sjmunroe at us dot ibm dot com  2008-06-26 14:12 -------
HJ this is the proposal I mentioned to you at GCC Summit. It way for each
platform to inline the isnan, isinf, finite, etc test in the libm function
wrappers (i.e w_pow.c)

Is uses macros defined in math-private.h to inline the various (redundent) tests
required to set errno (if needed). The generic ./math/math_private.h maintains
the status quo, but a platform can override math_private.h to define macros that
work best for them.

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[Bug math/6406] Improve performance of libm wrapper functions.

[hjl dot tools at gmail dot com]

------- Additional Comments From hjl dot tools at gmail dot com  2008-06-27 15:34 -------
(In reply to comment #5)
> HJ this is the proposal I mentioned to you at GCC Summit. It way for each
> platform to inline the isnan, isinf, finite, etc test in the libm function
> wrappers (i.e w_pow.c)
> 
> Is uses macros defined in math-private.h to inline the various (redundent) tests
> required to set errno (if needed). The generic ./math/math_private.h maintains
> the status quo, but a platform can override math_private.h to define macros that
> work best for them.

I will take a look at x86-64.

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