Disable threading through latches until after loop optimizations.

Disable threading through latches until after loop optimizations.

The motivation for this patch was enabling the use of global ranges in
the path solver, but this caused certain properties of loops being
destroyed which made subsequent loop optimizations to fail.
Consequently, this patch's mail goal is to disable jump threading
involving the latch until after loop optimizations have run.

As can be seen in the test adjustments, we mostly shift the threading
from the early threaders (ethread, thread[12] to the late threaders
thread[34]).  I have nuked some of the early notes in the testcases
that came as part of the jump threader rewrite.  They're mostly noise
now.

Note that we could probably relax some other restrictions in
profitable_path_p when loop optimizations have completed, but it would
require more testing, and I'm hesitant to touch more things than needed
at this point.  I have added a reminder to the function to keep this
in mind.

Finally, perhaps as a follow-up, we should apply the same restrictions to
the forward threader.  At some point I'd like to combine the cost models.

Tested on x86-64 Linux.

p.s. There is a thorough discussion involving the limitations of jump
threading involving loops here:

	https://gcc.gnu.org/pipermail/gcc/2021-September/237247.html

gcc/ChangeLog:

	* tree-pass.h (PROP_loop_opts_done): New.
	* gimple-range-path.cc (path_range_query::internal_range_of_expr):
	Intersect with global range.
	* tree-ssa-loop.c (tree_ssa_loop_done): Set PROP_loop_opts_done.
	* tree-ssa-threadbackward.c
	(back_threader_profitability::profitable_path_p): Disable
	threading through latches until after loop optimizations have run.

gcc/testsuite/ChangeLog:

	* gcc.dg/tree-ssa/ssa-dom-thread-2b.c: Adjust for disabling of
	threading through latches.
	* gcc.dg/tree-ssa/ssa-dom-thread-6.c: Same.
	* gcc.dg/tree-ssa/ssa-dom-thread-7.c: Same.

Co-authored-by: Michael Matz <matz@suse.de>