On 8/19/26 03:21, Andrea Pinski wrote:
On Tue, Aug 18, 2026 at 4:16 PM Andrew MacLeod <[email protected]> wrote:
My patch for 126329 allows early removal of builtin_unreachable to
proceed by replacing dead statements with an assignment to zero instead
of removing them.
In theory that was safe because there were no uses of the name in the
IL. The fallout was that if there was an existing equivalence or
relation with some other ssa name, this made those equivalences and
relations now relative to [0, 0]. oops.
I looked at a few options, and they all seemed a bit hacky.. In the end,
Ive provided a way to remove all relevant information about a range from
all the various components... Ranger, the relation oracle, the inferred
range oracle, and gori. Although this might seem like a bit of
overkill, it fills a gap that was uncovered a few months ago with
reset_flow_sensitive_info.
There are uses of reset_flow_sensitive_info (name) sprinkled around the
compiler which currently kills just the SSA_NAME_RANGE_INFO for an SSA
NAME. It won't affect ranger or any other component, and this may lead
to behaviour the developer is not expecting.
With this patch, a range_query object now has a reset_range_info ()
which is called by reset_flow_sensitive_info () and corrects this
situation. It will clear any range info from the current range object,
as well as the various oracles.. relations, inferred ranges, and gori.
Its a bit heavy handed but does a full job. I had considered just
clearing some of the cache flags, but if the ssa_name were to be used
again (and other use cases may expect that) some of the old relations
would have popped back into existence. This now expunges all of them.
Overall compile time building gcc is actually a wash.
The DCE fix for this PR now simply calls reset_flow_sensitive_info on
the ssa-name when it rewrites the statement to be an assignment of 0.
This clears all the information that may cause issues, and life is
hopefully good again.
The only problem with this is during forwprop (and other passes), we
save off the flow sensitive info and then restore it.
It uses reset_flow_sensitive_info to clear it but we only save off the
global ranges (or the global pointer data) for that ssa name.
So now we never restore the equivalents here.
But do those passes that "save" flow information use ranger? if they
aren't using ranger, then there are no active oracles or context
sensitive flow information to be cleared. Those equivalences and such
are only for the duration of a pass.
If they are using ranger, that seems like a problem if they are
saving information and restoring it but leaving rangers info alone.
See flow_sensitive_info_storage class in tree-ssanames.cc and its
usage in tree-ssa-forwprop.cc . So this could cause some performance
issues with some code paths happening and such.
If ranger isn't active those calls do nothing.
Thanks,
Andrea
Bootstraps on x86_64-pc-linux-gnu with no regressions. Pushed.
Andrew
