[patch, fortran] Fix PR 43072

[Thomas Koenig]

Hello world,

the attached patch fixes a missed optimization where a substring equal
in length to the original variable currently leads to an unneeded
temporary.

Regression-tested. OK for trunk?

Regards

	Thomas

2019-01-15  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/43072
	* resolve.c (resolve_array_ref): Add equal_length argument; set it
	if the length of the substring equals that of the orignal
	variable.
	(resolve_ref): Remove the substring if it is equal in length
	length to the original variable, unless it is an EXPR_SUBSTRING).

2019-01-15  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/43072
	* gfortran.dg/actual_array_substr_3.f90: New test.
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