[Bug middle-end/21067] Excessive optimization of floating point expression

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21067

Richard Guenther rguenth at gcc dot gnu.org changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution||INVALID

--- Comment #6 from Richard Guenther rguenth at gcc dot gnu.org 2012-01-11 
12:59:04 UTC ---
Invalid as per comment #4.

[Bug middle-end/21067] Excessive optimization of floating point expression

[vincent at vinc17 dot org]

--- Comment #5 from vincent at vinc17 dot org  2006-05-22 01:08 ---
IMHO, -frounding-math should be the default, unless -ffast-math is given.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21067

[Bug middle-end/21067] Excessive optimization of floating point expression

[roger at eyesopen dot com]

--- Comment #4 from roger at eyesopen dot com  2006-05-20 15:14 ---
This problem is fixed by specifying the -frounding-math command line option,
which informs the compiler that non-default rounding modes may be used.
With gcc-3.4, specifying this command line option disables this potentially
problematic transformation.

Strangely, on mainline, it looks like this transformation is no longer
triggered, which may now indicate a missed optimization regression with
(the default) -fno-rounding-math.  We should also catch the division case.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21067

[Bug middle-end/21067] Excessive optimization of floating point expression

[vincent at vinc17 dot org]

--- Additional Comments From vincent at vinc17 dot org  2005-06-15 16:42 
---
Even without fenv.h, the function could be in a library called in a directed
rounding mode.

And one can change the rounding mode via a standard function in the glibc, no
need for a pragma.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21067

[Bug middle-end/21067] Excessive optimization of floating point expression

[vincent at vinc17 dot org]

-- 
   What|Removed |Added

 CC||vincent at vinc17 dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21067

[Bug middle-end/21067] Excessive optimization of floating point expression

[pinskia at gcc dot gnu dot org]

--- Additional Comments From pinskia at gcc dot gnu dot org  2005-04-17 
07:34 ---
Note GCC does not know about the rounding mode, in fact the round mode is only 
changeable in C99 
by the #pragma which GCC does not do right now and I thought that is a 
different PR already.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21067

[Bug middle-end/21067] Excessive optimization of floating point expression

[bagnara at cs dot unipr dot it]

--- Additional Comments From bagnara at cs dot unipr dot it  2005-04-17 
08:52 ---
Subject: Re:  Excessive optimization of floating point
 expression

pinskia at gcc dot gnu dot org wrote:
 Note GCC does not know about the rounding mode,

This seems a good reason not to attempt optimizations
that only work with a given rounding mode.

 in fact the round mode is only changeable in C99 
 by the #pragma which GCC does not do right now and  I thought that is a 
 different PR already.

I do not see the connection with the #pragma you are talking about.

IMHO, a program that uses the services of fenv.h, which is
covered by section 7.6 of the C99 standard, is a perfectly
legal C99 program, and thus deserves to be compiled correctly
as prescribed by that standard.
Am I missing something?
All the best,

 Roberto



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21067