tree-optimization/114589 - remove profile based sink heuristics

tree-optimization/114589 - remove profile based sink heuristics

The following removes the profile based heuristic limiting sinking
and instead uses post-dominators to avoid sinking to places that
are executed under the same conditions as the earlier location which
the profile based heuristic should have guaranteed as well.

To avoid regressing this moves the empty-latch check to cover all
sink cases.

It also stream-lines the resulting select_best_block a bit but avoids
adjusting heuristics more with this change.  gfortran.dg/streamio_9.f90
starts execute failing with this on x86_64 with -m32 because the
(float)i * 9.9999...e-7 compute is sunk across a STOP causing it
to be no longer spilled and thus the compare failing due to excess
precision.  The patch adds -ffloat-store to avoid this, following
other similar testcases.

This change fixes the testcase in the PR only when using -fno-ivopts
as otherwise VRP is confused.

	PR tree-optimization/114589
	* tree-ssa-sink.cc (select_best_block): Remove profile-based
	heuristics.  Instead reject sink locations that sink
	to post-dominators.  Move empty latch check here from
	statement_sink_location.  Also consider early_bb for the
	loop depth check.
	(statement_sink_location): Remove superfluous check.  Remove
	empty latch check.
	(pass_sink_code::execute): Compute/release post-dominators.

	* gfortran.dg/streamio_9.f90: Use -ffloat-store to avoid
	excess precision when not spilling.
	* g++.dg/tree-ssa/pr114589.C: New testcase.