On Thu, Nov 29, 2018 at 12:20 AM Jan Hubicka <hubi...@ucw.cz> wrote: > > > On Tue, Nov 20, 2018 at 6:55 PM bin.cheng <bin.ch...@linux.alibaba.com> > > wrote: > > > > > > Sender:Jan Hubicka <hubi...@ucw.cz> > > > Sent at:2018 Nov 5 (Mon) 22:21 > > > To:Richard Biener <richard.guent...@gmail.com> > > > Cc:bin.cheng <bin.ch...@linux.alibaba.com>; GCC Patches > > > <gcc-patches@gcc.gnu.org> > > > Subject:Re: [PATCH AutoFDO/2]Treat ZERO as common profile > > > probability/count > > > > > > > > > > > > On Wed, Oct 31, 2018 at 7:30 AM bin.cheng > > > > > <bin.ch...@linux.alibaba.com> wrote: > > > > > > > > > > > > Hi, > > > > > > In new profile probability/count infra, we have different precision > > > > > > quality categories, > > > > > > and probabilities/counts of different categories are not supposed > > > > > > to be compared or > > > > > > calculated. Though in general is an improvement, it introduces > > > > > > unexpected behavior. > > > > > > Specifically, class profile_probablity and profile_count themselves > > > > > > are implemented > > > > > > by comparing probabilities/counts against profile_count::zero(). > > > > > > while zero() is of > > > > > > profile_precision category, it's always compared different to zero > > > > > > of other precision > > > > > > categories including afdo. > > > > > > > > > > > > I can see two ways fixing this: 1) Treat zero as a common > > > > > > probability/count regardless > > > > > > of its category; 2) Provide an "is_zero" method rather than relying > > > > > > on "==" comparison > > > > > > against probability_count::zero(). 2) requires lots of code > > > > > > changes so I went with 1) > > > > > > in this patch set. This patch doesn't handle "always" but it might > > > > > > be. > > > > > > > > > > > > This patch also corrects a minor issue where we try to invert an > > > > > > uninitialized value. > > > > > > > > > > > > Bootstrap and test on x86_64 in patch set. Is it OK? > > > > > > > > > > I'll defer on the emit_store_flag_force change, likewise for the zero > > > > > handling in > > > > > compares - I don't think zeros of different qualities should compare > > > > > equal. > > > > > Would compares against ::always() not have the very same issue? > > > > > Likewise ::even(), > > > > > ::likely(), etc.? Those always get guessed quality. > > > > > > > > > > The invert change looks OK to me. The related change to the always() > > > > > API would > > > > > suggest to replace guessed_always() with always (guessed) and also do > > > > > similar > > > > > changes throughout the whole API... > > > > > > > > > > Honza? > > > > > > > > The zeros are really differenct zeros. profile_count::zero makes us to > > > > drop the basic block into cold section because we know that it won't be > > > > executed in normal run of program (either we have accurate profile > > > > feedback or by proving that the program is on way to crash or user > > > > annotated cold section). Having guessed zero or auto-fdo zero won't > > > > make us to do such agressive size optimization. > > > > This is important since those zeros relatively commonly happens by > > > > accident and thus if we dropped all the code to cold section the cold > > > > section would be visited relativel often during execution of program > > > > which would eliminate its need. > > > > > > > > Most comparsion in profile-count.h which goes agains profile_count==zero > > > > are realy intended to pass only for this "aboslute zero". They bypass > > > > the precision adjusmtents which normally happen when you merge values > > > > of different precision. > > > > > > > > What kind of unexpected behaviour are you seeing? > > > > We already have nonzero_p which is what we use when we want to know that > > > > count is non-zero in some sense of precision. > > > Hi Honza, > > > Sorry for letting this slip away. So in case of AutoFDO, due to the > > > nature > > > of sampling, lots of funcs/bbs are annotated with zero profile_count in > > > afdo > > > precision, and we have checks against zero profile_count in precise > > > precision > > > All these checks end up with false and cause issues. Take the code in > > > update_profiling_info as an example: > > > > > > update_profiling_info (struct cgraph_node *orig_node, > > > struct cgraph_node *new_node) > > > { > > > struct cgraph_edge *cs; > > > struct caller_statistics stats; > > > profile_count new_sum, orig_sum; > > > profile_count remainder, orig_node_count = orig_node->count; > > > > > > if (!(orig_node_count.ipa () > profile_count::zero ())) > > > return; > > > //... > > > for (cs = new_node->callees; cs; cs = cs->next_callee) > > > cs->count = cs->count.apply_scale (new_sum, orig_node_count); > > > > > > Since we also have below code in profile_count::operator>, > > > if (other == profile_count::zero ()) > > > return !(*this == profile_count::zero ()); > > > > > > If orig_node_count is afdo zero, the above zero check for orig_node_count > > > returns false, we end up with passing zero density to apply_scale issue > > > and > > > asserting. > > > > > > In this updated patch, I restrcited changes only to > > > profile_count::operator > > > <, >, <= and >=. Plus, I think there is a latent typo in operator>= > > > because > > > current code return TRUE if '*this' is precise zero and 'other' is precise > > > non-zero. > > > @@ -879,7 +879,7 @@ public: > > > if (other == profile_count::zero ()) > > > return true; > > > if (*this == profile_count::zero ()) > > > - return !(other == profile_count::zero ()); > > > + return !other.nonzero_p (); > > We already have > > True: > profile_count::zero < any other value > any other value > profile_count::zero > profile_count::zero <= any initialized value > profile_count::zero <= profile_count::zero > any initialized value >= profile_count::zero > > false > profile_count::zero > any other value > any other value < profile_count::zero > > You are right about typo in >=, it should be: > > Index: profile-count.h > =================================================================== > --- profile-count.h (revision 266450) > +++ profile-count.h (working copy) > @@ -879,7 +879,7 @@ > if (other == profile_count::zero ()) > return true; > if (*this == profile_count::zero ()) > - return !(other == profile_count::zero ()); > + return other == profile_count::zero (); > gcc_checking_assert (compatible_p (other)); > return m_val >= other.m_val; > } > > With your patch we get false for: > profile_count::zero < guessed/auto_fdo/other 0 > guessed/auto_fdo/other > profile_count::zero > guessed/auto_fdo/other <= profile_count::zero > profile_count::zero >= profile_count::zero > > The original idea was to intentionally make profile_count::zero smaller > than any toher types of initialized values, since it is more strict hint > that the path will not be taken. > For example in bb_reorder if you end up with "funny" profile with two > exit edges one having profile_count::zero and other being zero as result > of (unsucesfull) profile updates it is still better idea to pick the > profile_count::zero for taken edge. With your patch it will end up > picking either of the paths. > > How the patch helps to your situation? Hi Honza, thanks very much for elaborating. Issue in case of autofdo is as described in last message: Given update_profiling_info implemented as below:
update_profiling_info (struct cgraph_node *orig_node, struct cgraph_node *new_node) { struct cgraph_edge *cs; struct caller_statistics stats; profile_count new_sum, orig_sum; profile_count remainder, orig_node_count = orig_node->count; //*****Operator ">" returns true if orig_node_count == autofdo.zero. if (!(orig_node_count.ipa () > profile_count::zero ())) return; //... for (cs = new_node->callees; cs; cs = cs->next_callee) //*****Result in apply_scale called with autofdo.zero as the 2nd argument. cs->count = cs->count.apply_scale (new_sum, orig_node_count); Also apply_scale is implemented as: profile_count apply_scale (profile_count num, profile_count den) const { if (*this == profile_count::zero ()) return *this; if (num == profile_count::zero ()) return num; if (!initialized_p () || !num.initialized_p () || !den.initialized_p ()) return profile_count::uninitialized (); if (num == den) return *this; gcc_checking_assert (den.m_val); Here we have (num != zero && den == autofdo.zero), it triggers the gcc_checking_assert. According to your explanation, guess we need to call force_nonzero for orig_node_count before calling apply_scale, right? Thanks, bin