On Tue, Nov 2, 2021 at 2:27 PM Richard Biener <richard.guent...@gmail.com> wrote: > > On Mon, Nov 1, 2021 at 2:03 PM Jeff Law via Gcc-patches > <gcc-patches@gcc.gnu.org> wrote: > > > > > > > > On 11/1/2021 3:54 AM, Aldy Hernandez wrote: > > > Chasing down stage3 miscomparisons is never fun, and having no way to > > > distinguish between jump threads registered by a particular > > > pass, is even harder. This patch adds debug counters for the individual > > > back threading passes. I've left the ethread pass alone, as that one is > > > usually benign, but we could easily add it if needed. > > > > > > The fact that we can only pass one boolean argument to the passes > > > infrastructure has us do all sorts of gymnastics to differentiate > > > between the various back threading passes. > > > > > > Tested on x86-64 Linux. > > > > > > OK? > > > > > > gcc/ChangeLog: > > > > > > * dbgcnt.def: Add debug counter for back_thread[12] and > > > back_threadfull[12]. > > > * passes.def: Pass "first" argument to each back threading pass. > > > * tree-ssa-threadbackward.c (back_threader::back_threader): Add > > > first argument. > > > (back_threader::debug_counter): New. > > > (back_threader::maybe_register_path): Call debug_counter. > > OK > > But it's ugly. Very. Why isn't a single debug-counter good enough? > You should be able to reduce to a single threading pass via > -fdisable-tree-xyz and then bisect with the debug counter.
Indeed. I'm not a big fan either. The -fdisable-tree-xyz approach is my first line of defense, but sometimes the problem is a combination of threading passes working in tandem. For example, thread1 threads a path that causes a later thread99 pass to find another path. So I can't just have one counter. We need to be able to bisect the thread1 path, and then, if there's still a problem, bisect the thread99 pass. I was fighting a bootstrap miscomparison bug when I could reduce the problem to 2 threading passes, and then further to thread1's 123 path, and thread2's 567 and 890 paths. Not fun. Aldy > > Alternatively at least store the debug counter to query somewhere > so you can have the "hot" path query a single one. So instead of > > if (!dbg_cnt (back_thread1)) > > do > > if (!dbg_cnt (curr_cnt)) > > and compute curr_cnt somewhere. > > Richard. > > > jeff > > >
