On 11/4/25 08:43, Richard Biener wrote:
The following implements additional checking around
SSA immediate use iteration. Specifically this prevents
- any nesting of FOR_EACH_IMM_USE_STMT inside another iteration
via FOR_EACH_IMM_USE_STMT or FOR_EACH_IMM_USE_FAST when iterating
on the same SSA name
- modification (for now unlinking of immediate uses) of a SSA
immediate use list when a fast iteration of the immediate uses
of the SSA name is active
- modification (for now unlinking of immediate uses) of the immediate
use list outside of the block of uses for the currently active stmt
of an ongoing FOR_EACH_IMM_USE_STMT of the SSA name
To implement this additional bookkeeping members are put into the
SSA name structure when ENABLE_GIMPLE_CHECKING is active. I have
kept the existing consistency checking of the fast iterator.
The patch depends on the previous one removing the fake sentinel
immediate use entry. Depends only in sofar that it doesn't apply
on trunk directly at the moment.
Boostrapped and tested on x86_64-unknown-linux-gnu, ontop of
the other patches.
Any further comments? I've seen no comment on the very first
change yet which was removal of the sentinel element (to fix
the ranger interaction)?
I only noticed that yesterday :-)
The sentinels purpose was to make sure adjusting a stmt would be safe
when things are removed. It serves as a guarantee the next pointer will
be valid. I am not opposed to replacing it with something more
modern.. (that code is about 20 years old) as long as there are enough
guardrails to deal with the additional case(s) that would be introduce.
In particular, the sentinel allows the remainder of the use list to
change, including the thing it points to. If the pointer to next
is stashed before any updates, there is a danger what it points to may
change... so that would have to be dissallowed and verified.
I think your listed guardrails should accomplish that. They will trap
in any place that attempts to make those modifications? which means
those passes can then be fixed their poor use of immediate uses...
If this is going in shortly, we don't need my FAST patch that skips the
soon to be nonexistent sentinel eh?.
Andrew
