[Patch, Fortran] CAF dep (1/3): PR62278 - improve dependency.c's gfc_check_dependency's check (missed-optimization)

[Tobias Burnus]

The current gfc_check_dependency check always looked at the pointer 
attribute - and assumed the worst, if either the LHS or the RHS was true.

Thus, it claimed that "a" and "b" alias for the following definition:  
integer, pointer :: p;  integer :: a. However, as "a" has no target (or 
pointer) attribute, that's not possible. Additionally, "class(t) :: a" 
has internally the "pointer" attribute (but 
CLASS_DATA(sym)->attr.class_pointer == 0), however, in the Fortran 
sense, "a" is not a pointer and cannot alias.

I do not have a good example for the test case, except for a similar one 
as above using "a[i] = p" and looking at the dump; but that requires 
patch 3/3 of this series.

Build and regtested on x86-64-gnu-linux. (I do get a failure for 
gfortran.dg/graphite/pr42393.f90, but only with -O1 -fgraphite-identity 
and also without the patch.)

OK for the trunk?

Tobias
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