[PATCH] Reuse the saved_scope structures allocated by push_to_top_level
push_to_top_level gets called fairly frequently in template-heavy code that performs a lot of instantiations, and we currently "leak" a lot of GC memory when compiling such code since [push|pop]_to_top_level() do not bother reusing or even freeing each saved_scope structure it allocates. This patch makes push_to_top_level() reuse the saved_scope structures it allocates. This is similar to how begin_scope() reuses the cp_binding_level structures it allocates. This patch reduces the maximum memory usage of the compiler by 4.5%, from 525MB to 500MB, when compiling the Boost::Fusion test file libs/fusion/test/compile_time/transform.cpp from the Boost 1.60 testsuite. Bootstrapped and tested on x86_64-pc-linux-gnu, OK for trunk or for GCC 7? gcc/cp/ChangeLog: * name-lookup.c (free_saved_scope): New free list of saved_scope structures. (push_to_top_level): Attempt to reuse a saved_scope struct from free_saved_scope instead of allocating a new one each time. (pop_from_top_level_1): Chain the now-unused saved_scope structure onto free_saved_scope. --- gcc/cp/name-lookup.c | 25 - 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c index 89d84d7..3478b6a 100644 --- a/gcc/cp/name-lookup.c +++ b/gcc/cp/name-lookup.c @@ -6134,6 +6134,10 @@ store_class_bindings (vec *names, timevar_cond_stop (TV_NAME_LOOKUP, subtime); } +/* A chain of saved_scope structures awaiting reuse. */ + +static GTY((deletable)) struct saved_scope *free_saved_scope; + void push_to_top_level (void) { @@ -6144,7 +6148,21 @@ push_to_top_level (void) bool need_pop; bool subtime = timevar_cond_start (TV_NAME_LOOKUP); - s = ggc_cleared_alloc (); + + /* Reuse or create a new structure for this saved scope. */ + if (free_saved_scope != NULL) +{ + s = free_saved_scope; + free_saved_scope = s->prev; + + vec *old_bindings = s->old_bindings; + memset (s, 0, sizeof (*s)); + /* Also reuse the structure's old_bindings vector. */ + vec_safe_truncate (old_bindings, 0); + s->old_bindings = old_bindings; +} + else +s = ggc_cleared_alloc (); b = scope_chain ? current_binding_level : 0; @@ -6237,6 +6255,11 @@ pop_from_top_level_1 (void) current_function_decl = s->function_decl; cp_unevaluated_operand = s->unevaluated_operand; c_inhibit_evaluation_warnings = s->inhibit_evaluation_warnings; + + /* Make this saved_scope structure available for reuse by + push_to_top_level. */ + s->prev = free_saved_scope; + free_saved_scope = s; } /* Wrapper for pop_from_top_level_1. */ -- 2.8.0.rc0.11.g9bfbc33
Re: [PATCH] Reuse the saved_scope structures allocated by push_to_top_level
On 2016.03.03 at 09:16 -0500, Patrick Palka wrote: > push_to_top_level gets called fairly frequently in template-heavy code > that performs a lot of instantiations, and we currently "leak" a lot of > GC memory when compiling such code since [push|pop]_to_top_level() do > not bother reusing or even freeing each saved_scope structure it > allocates. > > This patch makes push_to_top_level() reuse the saved_scope structures it > allocates. This is similar to how begin_scope() reuses the > cp_binding_level structures it allocates. > > This patch reduces the maximum memory usage of the compiler by 4.5%, > from 525MB to 500MB, when compiling the Boost::Fusion test file > libs/fusion/test/compile_time/transform.cpp from the Boost 1.60 testsuite. > > Bootstrapped and tested on x86_64-pc-linux-gnu, OK for > trunk or for GCC 7? Great. push_to_top_level also shows up very high in profiles when building Chromium for example. There is an old bug for this issue: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64500 -- Markus
Re: [PATCH] Reuse the saved_scope structures allocated by push_to_top_level
On Thu, Mar 3, 2016 at 9:22 AM, Markus Trippelsdorf wrote: > On 2016.03.03 at 09:16 -0500, Patrick Palka wrote: >> push_to_top_level gets called fairly frequently in template-heavy code >> that performs a lot of instantiations, and we currently "leak" a lot of >> GC memory when compiling such code since [push|pop]_to_top_level() do >> not bother reusing or even freeing each saved_scope structure it >> allocates. >> >> This patch makes push_to_top_level() reuse the saved_scope structures it >> allocates. This is similar to how begin_scope() reuses the >> cp_binding_level structures it allocates. >> >> This patch reduces the maximum memory usage of the compiler by 4.5%, >> from 525MB to 500MB, when compiling the Boost::Fusion test file >> libs/fusion/test/compile_time/transform.cpp from the Boost 1.60 testsuite. >> >> Bootstrapped and tested on x86_64-pc-linux-gnu, OK for >> trunk or for GCC 7? > > Great. push_to_top_level also shows up very high in profiles when > building Chromium for example. > > There is an old bug for this issue: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64500 > > -- > Markus I forgot what exactly I was benchmarking but I also saw push_to_top_level high on the list which is what made me interested in this function in the first place. I think the slowness of this function is mostly due to the pointer chasing performed in the function store_bindings, where we iterate over all the names in each non-global scope to figure out whether to preserve them. It would probably improve performance if cp_binding_level::names were a vector of trees instead of a linked list of trees.
Re: [PATCH] Reuse the saved_scope structures allocated by push_to_top_level
On 03/03/16 14:49, Patrick Palka wrote: I think the slowness of this function is mostly due to the pointer chasing performed in the function store_bindings, where we iterate over all the names in each non-global scope to figure out whether to preserve them. It would probably improve performance if cp_binding_level::names were a vector of trees instead of a linked list of trees. It would be an overall improvement if it was neither a TREE_LIST, nor a TREE_VECTOR: https://gcc.gnu.org/wiki/Speedup_areas#Trees Those kinds of cleanups are always welcome even if they do not improve performance noticeably at first glance. The speed-up will show up once TREE_LIST is removed completely. Cheers, Manuel.
Re: [PATCH] Reuse the saved_scope structures allocated by push_to_top_level
On Thu, Mar 3, 2016 at 10:22 AM, Manuel López-Ibáñez wrote: > On 03/03/16 14:49, Patrick Palka wrote: >> >> I think the slowness of this function is mostly due to the pointer >> chasing performed in the function store_bindings, where we iterate >> over all the names in each non-global scope to figure out whether to >> preserve them. It would probably improve performance if >> cp_binding_level::names were a vector of trees instead of a linked >> list of trees. > > > It would be an overall improvement if it was neither a TREE_LIST, nor a > TREE_VECTOR: https://gcc.gnu.org/wiki/Speedup_areas#Trees > > Those kinds of cleanups are always welcome even if they do not improve > performance noticeably at first glance. The speed-up will show up once > TREE_LIST is removed completely. Ah yeah, I meant if cp_binding_level::names were a vec since it would have to be resizable. > > Cheers, > > Manuel. > >
Re: [PATCH] Reuse the saved_scope structures allocated by push_to_top_level
On 3 March 2016 at 15:39, Patrick Palka wrote: > On Thu, Mar 3, 2016 at 10:22 AM, Manuel López-Ibáñez > wrote: >> It would be an overall improvement if it was neither a TREE_LIST, nor a >> TREE_VECTOR: https://gcc.gnu.org/wiki/Speedup_areas#Trees >> >> Those kinds of cleanups are always welcome even if they do not improve >> performance noticeably at first glance. The speed-up will show up once >> TREE_LIST is removed completely. > > Ah yeah, I meant if cp_binding_level::names were a vec > since it would have to be resizable. Sure, what I meant is that such a change is an improvement even if you cannot measure any speed-up at all right now. Go for it! Cheers, Manuel.
Re: [PATCH] Reuse the saved_scope structures allocated by push_to_top_level
On Thu, Mar 3, 2016 at 9:16 AM, Patrick Palka wrote: > push_to_top_level gets called fairly frequently in template-heavy code > that performs a lot of instantiations, and we currently "leak" a lot of > GC memory when compiling such code since [push|pop]_to_top_level() do > not bother reusing or even freeing each saved_scope structure it > allocates. > > This patch makes push_to_top_level() reuse the saved_scope structures it > allocates. This is similar to how begin_scope() reuses the > cp_binding_level structures it allocates. > > This patch reduces the maximum memory usage of the compiler by 4.5%, > from 525MB to 500MB, when compiling the Boost::Fusion test file > libs/fusion/test/compile_time/transform.cpp from the Boost 1.60 testsuite. > > Bootstrapped and tested on x86_64-pc-linux-gnu, OK for > trunk or for GCC 7? > > gcc/cp/ChangeLog: > > * name-lookup.c (free_saved_scope): New free list of saved_scope > structures. > (push_to_top_level): Attempt to reuse a saved_scope struct > from free_saved_scope instead of allocating a new one each time. > (pop_from_top_level_1): Chain the now-unused saved_scope structure > onto free_saved_scope. > --- > gcc/cp/name-lookup.c | 25 - > 1 file changed, 24 insertions(+), 1 deletion(-) > > diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c > index 89d84d7..3478b6a 100644 > --- a/gcc/cp/name-lookup.c > +++ b/gcc/cp/name-lookup.c > @@ -6134,6 +6134,10 @@ store_class_bindings (vec > *names, >timevar_cond_stop (TV_NAME_LOOKUP, subtime); > } > > +/* A chain of saved_scope structures awaiting reuse. */ > + > +static GTY((deletable)) struct saved_scope *free_saved_scope; > + > void > push_to_top_level (void) > { > @@ -6144,7 +6148,21 @@ push_to_top_level (void) >bool need_pop; > >bool subtime = timevar_cond_start (TV_NAME_LOOKUP); > - s = ggc_cleared_alloc (); > + > + /* Reuse or create a new structure for this saved scope. */ > + if (free_saved_scope != NULL) > +{ > + s = free_saved_scope; > + free_saved_scope = s->prev; > + > + vec *old_bindings = s->old_bindings; > + memset (s, 0, sizeof (*s)); > + /* Also reuse the structure's old_bindings vector. */ > + vec_safe_truncate (old_bindings, 0); > + s->old_bindings = old_bindings; > +} > + else > +s = ggc_cleared_alloc (); > >b = scope_chain ? current_binding_level : 0; > > @@ -6237,6 +6255,11 @@ pop_from_top_level_1 (void) >current_function_decl = s->function_decl; >cp_unevaluated_operand = s->unevaluated_operand; >c_inhibit_evaluation_warnings = s->inhibit_evaluation_warnings; > + > + /* Make this saved_scope structure available for reuse by > + push_to_top_level. */ > + s->prev = free_saved_scope; > + free_saved_scope = s; > } > > /* Wrapper for pop_from_top_level_1. */ > -- > 2.8.0.rc0.11.g9bfbc33 > Ping.
Re: [PATCH] Reuse the saved_scope structures allocated by push_to_top_level
OK. Jason