Fix more ICEs in -fsave-optimization-record (PR tree-optimization/89235)

Fix more ICEs in -fsave-optimization-record (PR tree-optimization/89235)

PR tree-optimization/89235 reports an ICE inside -fsave-optimization-record
whilst reporting the inlining chain of of the location_t in the
vect_location global.

This is very similar to PR tree-optimization/86637, fixed in r266821.

The issue is that the inlining chains are read from the location_t's
ad-hoc data, referencing GC-managed tree blocks, but the former are
not GC roots; it's simply assumed that old locations referencing dead
blocks never get used again.

The fix is to reset the "vect_location" global in more places.  Given
that is a somewhat subtle detail, the patch adds a sentinel class to
reset vect_location at the end of a scope.  Doing it as a class
simplifies the task of ensuring that the global is reset on every
exit path from a function, and also gives a good place to signpost
the above subtlety (in the documentation for the class).

The patch also adds test cases for both of the PRs mentioned above.

gcc/testsuite/ChangeLog:
	PR tree-optimization/86637
	PR tree-optimization/89235
	* gcc.c-torture/compile/pr86637-1.c: New test.
	* gcc.c-torture/compile/pr86637-2.c: New test.
	* gcc.c-torture/compile/pr86637-3.c: New test.
	* gcc.c-torture/compile/pr89235.c: New test.

gcc/ChangeLog:
	PR tree-optimization/86637
	PR tree-optimization/89235
	* tree-vect-loop.c (optimize_mask_stores): Add an
	auto_purge_vect_location sentinel to ensure that vect_location is
	purged on exit.
	* tree-vectorizer.c
	(auto_purge_vect_location::~auto_purge_vect_location): New dtor.
	(try_vectorize_loop_1): Add an auto_purge_vect_location sentinel
	to ensure that vect_location is purged on exit.
	(pass_slp_vectorize::execute): Likewise, replacing the manual
	reset.
	* tree-vectorizer.h (class auto_purge_vect_location): New class.

From-SVN: r268659