On Wed, Apr 5, 2023 at 11:53 PM Jeff Law via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > > > On 4/5/23 14:10, Andrew MacLeod via Gcc-patches wrote: > > When a statement is first processed, any SSA_NAMEs that are dependencies > > are cached for quick future access. > > > > if we ;later rewrite the statement (say propagate a constant into it), > > its possible the ssa-name in this cache is no longer active. Normally > > this is not a problem, but the changed to may_recompute_p forgot to take > > that into account, and was checking a dependency from the cache that was > > in the SSA_NAME_FREE_LIST. It thus had no SSA_NAME_DEF_STMT when we were > > expecting one. > > > > This patch simply rejects dependencies from consideration if they are in > > the free list. > > > > Bootstrapping on x86_64-pc-linux-gnu and presuming no regressio0ns, OK > > for trunk? > eek. So you've got a released name in the cache? What happens if the > name gets released, then re-used? Aren't you going to get bogus results > in that case?
We never re-use SSA names from within the pass releasing it. But if the ranger cache persists across passes this could be a problem. See flush_ssaname_freelist which for example resets the SCEV hash table which otherwise would have the same issue. IIRC ranger never outlives a pass so the patch should be OK. _But_ I wonder how ranger gets at the tree SSA name in the first place - usually caches are indexed by SSA_NAME_VERSION (because that's cheaper and better than a pointer to the tree) and ssa_name (ver) will return NULL for released SSA names. So range_def_chain::rdc could be just struct rdc { int ssa1; // First direct dependency int ssa2; // Second direct dependency bitmap bm; // All dependencies bitmap m_import; }; and ::depend1 return ssa_name (m_def_chain[v].ssa1) and everything would work automatically (and save 8 bytes of storage). Richard. > jeff