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From: "law at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/95663] static_cast checks for null even when
 the pointer is dereferenced
Date: Sat, 27 Jun 2020 15:36:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95663

--- Comment #13 from Jeffrey A. Law <law at redhat dot com> ---
Marc,

Yes, absolutely.  In fact, I think that falls out of the work Martin S is d=
oing
in this space.  Conceptually we're looking to generalize that code so that =
we
can route more cases where the compiler detects undefined behavior through =
the
path isolation routines.

Within those commonized routines we want to have a knob which selects diffe=
rent
behavior from the compiler when undefined behavior is detected which could
potentially include issuing the RTL equivalent of __builtin_unreachable vs =
trap
vs warn, but leave the code alone, try to mitigate, etc.

Where I think we've differed in the past is what to do with conditional bra=
nch
upon which the undefined behavior is control dependent upon.  As you may
remember, the original submission of path isolation would turn that conditi=
onal
into an unconditional branch to the valid path.  That's not correct because
there can be observable behavior that occurs on the path from the condition=
al,
but before the undefined behavior triggers.  Having a knob to twiddle *that*
may or may not be a good idea.=