Claw back some of the code size regression in 548.exchange2_r

Claw back some of the code size regression in 548.exchange2_r

This patch tries harder to detect cases in which the inner dimension
of an array access is invariant, such as:

     x(i, :) = 100

It fixes some of the code size regression in 548.exchange2_r, with
size improving by 5% compared to before the patch.  Of the two other
SPEC 2017 tests affected by loop versioning, 554.roms_r improved by a
trivial amount (0.3%) and 549.fotonik3d_r didn't change.  All three
results are with -Ofast -flto.

2019-01-19  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* gimple-loop-versioning.cc (loop_versioning::dump_inner_likelihood):
	New function, split out from...
	(loop_versioning::analyze_stride): ...here.
	(loop_versioning::find_per_loop_multiplication): Use gassign.
	(loop_versioning::analyze_term_using_scevs): Return a success code.
	(loop_versioning::analyze_arbitrary_term): New function.
	(loop_versioning::analyze_address_fragment): Use
	analyze_arbitrary_term if all else fails.

gcc/testsuite/
	* gfortran.dg/loop_versioning_1.f90: Bump the number of identified
	inner strides.
	* gfortran.dg/loop_versioning_9.f90: New test.
	* gfortran.dg/loop_versioning_10.f90: Likewise.

From-SVN: r268093