[gfortran,patch] New option to use BLAS routines for matrix multiplication

[FX Coudert]

Hi all,

The attached patch allows gfortran-compiled code to use the sgemm/ 
dgemm/cgemm/zgemm routines from BLAS to perform matrix  
multiplications. There is no big change from the last patch I posted.  
I'll say a few words about how it works, how I tested it, and then  
answer Janne's comments to my last patch.

OK for mainline?


*How does it work?*

The library functions matmul_{i,r,c}{4,8,10,16} take three extra  
arguments: int try_blas tells whether we want to try using a BLAS;  
int blas_limit is the size criterion for using BLAS or libgfortran  
code; the last argument is a pointer to the BLAS function to be used.

The front-end function gfc_conv_function_call (in trans-expr.c) is  
added an extra tree argument, which corresponds to arguments that  
will be added after all other function arguments. It's currently only  
used for the translation of MATMUL calls, but it could be used in the  
future e.g. bounds checking information.


*How did I test it?*

It was bootstrapped and regtested on i686-linux. I did some manual  
testing and timing on i686-linux, the result of which can be found  
here: http://www.eleves.ens.fr/home/coudert/timing.png These graphs  
report the execution time as a function of matrix size, for  
multiplication of square matrices of complex and real floating point  
kinds 4 and 8. Black curve is for unpatched gfortran, red is for  
patched gfortran with ATLAS (and size limit 0, i.e. all matrix  
multiplications performed by BLAS calls) and green is for patched  
gfortran with Intel MKL (again, size limit is 0).

I also attach to this file an ugly "regression-tester" I made. It  
builds matrices of all types, kinds, size and stride, and performs  
matrix multiplication by different means and compares the results. To  
compile and run:

$ gfortran -c matmul_blas.f90 -fexternal-blas -fblas-matmul-limit=0
$ gfortran matrix.F90 gemm.f90 matmul_blas.o  -ffree-line-length-none
$ ./a.out

The integer parameters nmax and ncheck in matrix.F90 can be changed  
and control the maximal size of the generated matrices, and the  
number of check cycles to run (the more the merrier, since some  
parameters are randomly chosen).


*Answers to Janne's comments* (http://gcc.gnu.org/ml/fortran/2006-09/ 
msg00380.html)

point 1) you're right

point 1b) the three size involved are xcount, ycount and count; the  
BLAS function is now called when the (geometric) mean of these is  
higher than the size limit specified; numbers are cast to float for  
calculations to avoid overflow

point 2) well, for what I have seen, the function call penalty is  
negligeable, especially since BLAS routines are used for heavy  
computations



:ADDPATCH fortran:
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