On Mon, Jul 26, 2021 at 11:07 PM Jeff Law <jeffreya...@gmail.com> wrote: > > > > On 7/25/2021 7:47 PM, Bin.Cheng wrote: > > On Sat, Jul 24, 2021 at 12:30 AM Jeff Law via Gcc-patches > > <gcc-patches@gcc.gnu.org> wrote: > >> > >> > >> On 7/14/2021 3:14 AM, bin.cheng via Gcc-patches wrote: > >>> Hi, > >>> I ran into a wrong code bug in code with deep template instantiation when > >>> working on sdx::simd. > >>> The root cause as described in commit summary is we skip prologue insns > >>> in init_alias_analysis. > >>> This simple patch fixes the issue, however, it's hard to reduce a case > >>> because of heavy use of > >>> templates. > >>> Bootstrap and test on x86_64, is it OK? > >> It's a clear correctness improvement, but what's unclear to me is why > >> we'd want to skip them in the epilogue either. > > I can only guess, there is nothing to initialize epilogue for because > > no code follows. > Yea, but couldn't the lack of analysis of the epilogue lead to a pass > mis-optimizing code within the epilogue itself? It's not terribly > likely, but it just seems wrong to skip the epilogue like this. > Remember, the aliasing bits are just an analysis phase to find the > aliasing relationships that exist and we don't necessarily know how that > data is going to be used. It may in fact be safe now, but may not be > safe in the future if someone added a late RTL pass that used the > aliasing info in a new way. > > The more I think about it, the more I think we should remove remove this > hunk of code completely. There is some chance for fallout, but I think > it's unlikely. Hi Jeff, Thanks for the suggestion, here is the simple patch removing all of it. diff --git a/gcc/alias.c b/gcc/alias.c index 69e1eb89ac6..099acabca6b 100644 --- a/gcc/alias.c +++ b/gcc/alias.c @@ -3406,14 +3406,6 @@ init_alias_analysis (void) rpo = XNEWVEC (int, n_basic_blocks_for_fn (cfun)); rpo_cnt = pre_and_rev_post_order_compute (NULL, rpo, false);
- /* The prologue/epilogue insns are not threaded onto the - insn chain until after reload has completed. Thus, - there is no sense wasting time checking if INSN is in - the prologue/epilogue until after reload has completed. */ - bool could_be_prologue_epilogue = ((targetm.have_prologue () - || targetm.have_epilogue ()) - && reload_completed); - pass = 0; do { @@ -3459,10 +3451,6 @@ init_alias_analysis (void) { rtx note, set; - if (could_be_prologue_epilogue - && prologue_epilogue_contains (insn)) - continue; - /* If this insn has a noalias note, process it, Otherwise, scan for sets. A simple set will have no side effects which could change the base value of any other register. */ No fallouts in bootstrap/test on x86_64. Is it OK? Thanks, bin > > Jeff >