_gfortran_pow_r4_i4 library calls

[Tobias Burnus]

Dennis Wassel wrote:
> I have compiled Lapack with gfortran 4.2.2 and am now trying to link
> against that library with gfortran 4.3.0.
> This results in my linker whining:
> slamch.f:(.text+0xaf): undefined reference to `_gfortran_pow_r4_i4'
>
> Checking this I found that the 3.0.0 Fortranlib does supply
> "_gfortran_pow_r4_i8" but not "_gfortran_pow_r4_i4", as the 2.0.0
> still does. Is this a bug or a feature? :-)
>   
Feature. Gfortran now uses in this case the __builtin_powif, which can 
be optimized further by the middle end of GCC.

Between 4.1 and 4.2 and 4.3 we did/do not guarantee that the library 
interface remains stable; within a stable branch it does. However, 
starting from 4.3.0 we use versioned symbols, i.e. on system where this 
is supported, all 4.3-compiled programs/libraries should work with 
libgfortran of later gfortran versions. (Which means that we will 
continue to carry stuff around which is unused using newer compilers.)

I have never experimented with it, but it might work to link to both 
libraries; assume you put libgfortran of 4.2.0 into a different 
directory, then linking with "-lgfortran -L<path to 4.2> -lgfortran" 
might work. However, even if it seems to work, this can cause some 
unexpected problems in some special cases.

Thus the safest way is indeed to recompile Lapack with gfortran 4.3. 
(Hoping that the [sd]lartg do not appear). If you don't have last years 
3.1.1. there would be even another good reason for it ;-)

Tobias