[Bug math/16296] New: fegetround is pure?

[Bug math/16296] New: fegetround is pure?

[marc.glisse at normalesup dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16296

            Bug ID: 16296
           Summary: fegetround is pure?
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: marc.glisse at normalesup dot org

I could be wrong, but it seems that the function fegetround could get
__attribute_pure__, since it only reads a global state, and in particular the
usual optimizations (remove it if the result is unused, reuse the result from
the first call when there are two calls in a row) should be fine.

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[Bug math/16296] fegetround is pure?

[bugdal at aerifal dot cx]

https://sourceware.org/bugzilla/show_bug.cgi?id=16296

Rich Felker <bugdal at aerifal dot cx> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugdal at aerifal dot cx

--- Comment #1 from Rich Felker <bugdal at aerifal dot cx> ---
How do you expect the compiler to know it can't cache the result of fegetround
across calls to fesetround, fesetenv, etc.?

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[Bug math/16296] fegetround is pure?

[marc.glisse at normalesup dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16296

--- Comment #2 from Marc Glisse <marc.glisse at normalesup dot org> ---
(In reply to Rich Felker from comment #1)
> How do you expect the compiler to know it can't cache the result of
> fegetround across calls to fesetround, fesetenv, etc.?

Uh, the same as for any pure function? The definition of pure is that it only
depends on the arguments and global memory (as opposed to const, which only
depends on the arguments). Any non-pure function call like fesetround clobbers
global memory and the compiler knows that caching becomes invalid then.

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[Bug math/16296] fegetround is pure?

[bugdal at aerifal dot cx]

https://sourceware.org/bugzilla/show_bug.cgi?id=16296

--- Comment #3 from Rich Felker <bugdal at aerifal dot cx> ---
I was probably confusing it with attribute const...

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[Bug math/16296] fegetround is pure?

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=16296

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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[Bug math/16296] fegetround is pure?

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16296

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |2.23

--- Comment #5 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
Fixed for 2.23.

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[Bug math/16296] fegetround is pure?

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=16296

--- Comment #4 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
This is an automated email from the git hooks/post-receive script. It was
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The branch, master has been updated
       via  223d1cacc5dafe8af53e84608c2d130721c4edcd (commit)
      from  0b87419b690d1711697ed95808527400910ff997 (commit)

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=223d1cacc5dafe8af53e84608c2d130721c4edcd

commit 223d1cacc5dafe8af53e84608c2d130721c4edcd
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Sep 15 20:36:50 2015 +0000

    Mark fegetround pure (bug 16296).

    Bug 16296 notes that fegetround is a pure function and should be
    marked as such in fenv.h.  This patch implements that.

    Tested for x86_64 and x86 (testsuite, and that installed stripped
    shared libraries are unchanged by this patch).

        [BZ #16296]
        * math/fenv.h (fegetround): Use __attribute_pure__.
        * include/fenv.h (__fegetround): Likewise.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog      |    4 ++++
 NEWS           |   12 ++++++------
 include/fenv.h |    2 +-
 math/fenv.h    |    2 +-
 4 files changed, 12 insertions(+), 8 deletions(-)

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