[patch, fortran] Create temporary variables for matmul

[Thomas Koenig]

Hello world,

the attached patch goes one step further in matmul inlinding.

It converts statements like

   r = dot_product(matmul(a2,v1),v2)

into

   tmp = matmul(a2,v1)
   r = dot_product(tmp,v2)

to enable inlining of matmul (but only if inlining
is active, of course).

In order to detect multiple uses of matmul, this is run
several times.  I did this because, with the current
implementation, create_var can fail if -fno-realloc-lhs
is specified.  This is also not optimal, but that's a bug
for another day, and I don't see any drawbacks in
code generation for this (the extra basic blocks will
be removed).

The actual overhead in the case of non-constant bounds should
be small to non-existent, this only replaces one type of
temporary with another.

I had to adjust some test cases which counted things to use
the library version.

Regression-tested.  OK for trunk?

Regards

	Thomas

P.S: Next on the agenda is to better handle the left-over combinations
for Matmul, and to create temporaries for dependencies and
function evaluations in the arguments that we currently do not
handle.

2017-05-07  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/79930
	* frontend-passes.c (matmul_to_var_expr): New function,
	add prototype.
	(matmul_to_var_code):  Likewise.
	(optimize_namespace):  Use them from gfc_code_walker.

2017-05-07  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/79930
	* gfortran.dg/inline_transpose_1.f90:  Add
	-finline-matmul-limit=0 to options.
	* gfortran.dg/matmul_5.f90:  Likewise.
	* gfortran.dg/vect/vect-8.f90: Likewise.
	* gfortran.dg/inline_matmul_14.f90:  New test.
	* gfortran.dg/inline_matmul_15.f90:  New test.
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