On Thu, Feb 19, 2026 at 5:06 AM Siddhesh Poyarekar <[email protected]> wrote: > > On 2026-02-18 22:46, Andrew Pinski wrote: > >> + /* Skip over inval_bb. */ > >> + if (inval_bb != from) > >> + for (auto gsi = gsi_start_bb (from); !gsi_end_p (gsi); > >> + gsi_next_nondebug (&gsi)) > >> + { > >> + gimple *stmt = gsi_stmt (gsi); > >> + if (gimple_code (stmt) == GIMPLE_ASSIGN > >> + && clobvar == gimple_assign_lhs (stmt)) > > > > I am not sure this is correct, this only works if clobvar does not escape. > > I think you need to use the alias oracle here to query if the stmt > > clobbers clobvar or not. > > Ugh, sorry, I don't think I even need that; I had tried to combine the > loop in use_after_inval_p with this but that didn't work. Given that we > know that the use simply straight-lines into the exit block when this is > called, I think we could simply walk through the BBs to determine > reachability without looking for intervening clobbers/inits; the > intervening statements only show up in loops. I'll test and confirm.
Also is 'clobvar' an SSA name? In that case, when you reach CFG merges, you have to translate through PHIs. If it is not a SSA name and you are looking at memory you can use faster traversal of SSA_NAME_DEF_STMT of the VUSEs. > > Also I don't like introducing an extra walk of the IR . Especially > > since this would be O(SUM(STMT,BB)) . > > There must be a way to tell quickly if there is a path from BB1 to BB2 > > without walking the CFG. > I looked but couldn't find one :/ Let me take another look around to > see if I find something. There is none (well, you can walk the CFG only, not stmts). You can do quick dominator checks first. IMO when we commit to emit a diagnostic it's OK to spend "unreasonable" time to prune it (we can always add sth like a --param to limit the work to prune). Richard. > > Thanks, > Sid
