aarch64: Ensure iterator validity when updating debug uses [PR113616]

The fix for PR113089 introduced range-based for loops over the
debug_insn_uses of an RTL-SSA set_info, but in the case that we reset a
debug insn, the use would get removed from the use list, and thus we
would end up using an invalidated iterator in the next iteration of the
loop.  In practice this means we end up terminating the loop
prematurely, and hence ICE as in PR113089 since there are debug uses
that we failed to fix up.

This patch fixes that by introducing a general mechanism to avoid this
sort of problem.  We introduce a safe_iterator to iterator-utils.h which
wraps an iterator, and also holds the end iterator value.  It then
pre-computes the next iterator value at all iterations, so it doesn't
matter if the original iterator got invalidated during the loop body, we
can still move safely to the next iteration.

We introduce an iterate_safely helper which effectively adapts a
container such as iterator_range into a container of safe_iterators over
the original iterator type.

We then use iterate_safely around all loops over debug_insn_uses () in
the aarch64 ldp/stp pass to fix PR113616.  While doing this, I
remembered that cleanup_tombstones () had the same problem.  I
previously worked around this locally by manually maintaining the next
nondebug insn, so this patch also refactors that loop to use the new
iterate_safely helper.

While doing that I noticed that a couple of cases in cleanup_tombstones
could be converted from using dyn_cast<set_info *> to as_a<set_info *>,
which should be safe because there are no clobbers of mem in RTL-SSA, so
all defs of memory should be set_infos.

gcc/ChangeLog:

	PR target/113616
	* config/aarch64/aarch64-ldp-fusion.cc (fixup_debug_uses_trailing_add):
	Use iterate_safely when iterating over debug uses.
	(fixup_debug_uses): Likewise.
	(ldp_bb_info::cleanup_tombstones): Use iterate_safely to iterate
	over nondebug insns instead of manually maintaining the next insn.
	* iterator-utils.h (class safe_iterator): New.
	(iterate_safely): New.

gcc/testsuite/ChangeLog:

	PR target/113616
	* gcc.c-torture/compile/pr113616.c: New test.

0 files changed, 0 insertions, 0 deletions