On Fri, 18 Nov 2022, apinski--- via Gcc-patches wrote: > From: Andrew Pinski <apin...@marvell.com> > > Since we use C++11 by default now, we can > use constexpr for some const decls in tree-core.h. > > This patch does that and it allows for better optimizations > of GCC code with checking enabled and without LTO. > > For an example generic-match.cc compiling is speed up due > to the less number of basic blocks and less debugging info > produced. I did not check the speed of compiling the same source > but rather the speed of compiling the old vs new sources here > (but with the same compiler base). > > The small slow down in the parsing of the arrays in each TU > is migrated by a speed up in how much code/debugging info > is produced in the end. > > Note I looked at generic-match.cc since it is one of the > compiling sources which causes parallel building to stall and > I wanted to speed it up. > > OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions. > Or should this wait until GCC 13 branches off? > > gcc/ChangeLog: > > PR middle-end/14840 > * tree-core.h (tree_code_type): Constexprify > by including all-tree.def. > (tree_code_length): Likewise. > * tree.cc (tree_code_type): Remove. > (tree_code_length): Remove. > --- > gcc/tree-core.h | 21 +++++++++++++++++++-- > gcc/tree.cc | 24 ------------------------ > 2 files changed, 19 insertions(+), 26 deletions(-) > > diff --git a/gcc/tree-core.h b/gcc/tree-core.h > index af75522504f..e146b133dbd 100644 > --- a/gcc/tree-core.h > +++ b/gcc/tree-core.h > @@ -2284,15 +2284,32 @@ struct floatn_type_info { > /* Matrix describing the structures contained in a given tree code. */ > extern bool tree_contains_struct[MAX_TREE_CODES][64]; > > +#define DEFTREECODE(SYM, NAME, TYPE, LENGTH) TYPE, > +#define END_OF_BASE_TREE_CODES tcc_exceptional, > + > + > /* Class of tree given its code. */ > -extern const enum tree_code_class tree_code_type[]; > +constexpr enum tree_code_class tree_code_type[] = { > +#include "all-tree.def" > +}; > + > +#undef DEFTREECODE > +#undef END_OF_BASE_TREE_CODES > > /* Each tree code class has an associated string representation. > These must correspond to the tree_code_class entries. */ > extern const char *const tree_code_class_strings[]; > > /* Number of argument-words in each kind of tree-node. */ > -extern const unsigned char tree_code_length[]; > + > +#define DEFTREECODE(SYM, NAME, TYPE, LENGTH) LENGTH, > +#define END_OF_BASE_TREE_CODES 0, > +constexpr unsigned char tree_code_length[] = { > +#include "all-tree.def" > +}; > + > +#undef DEFTREECODE > +#undef END_OF_BASE_TREE_CODES
IIUC defining these globals as non-inline constexpr gives them internal linkage, and so each TU contains its own unique copy of these globals. This bloats cc1plus by a tiny bit and is technically an ODR violation because some inline functions such as tree_class_check also ODR-use these variables and so each defn of tree_class_check will refer to a "different" tree_code_class. Since inline variables are a C++17 feature, I guess we could fix this by defining the globals the old way before C++17 and as inline constexpr otherwise? > > /* Vector of all alias pairs for global symbols. */ > extern GTY(()) vec<alias_pair, va_gc> *alias_pairs; > diff --git a/gcc/tree.cc b/gcc/tree.cc > index 574bd2e65d9..254b2373dcf 100644 > --- a/gcc/tree.cc > +++ b/gcc/tree.cc > @@ -74,31 +74,7 @@ along with GCC; see the file COPYING3. If not see > #include "asan.h" > #include "ubsan.h" > > -/* Tree code classes. */ > > -#define DEFTREECODE(SYM, NAME, TYPE, LENGTH) TYPE, > -#define END_OF_BASE_TREE_CODES tcc_exceptional, > - > -const enum tree_code_class tree_code_type[] = { > -#include "all-tree.def" > -}; > - > -#undef DEFTREECODE > -#undef END_OF_BASE_TREE_CODES > - > -/* Table indexed by tree code giving number of expression > - operands beyond the fixed part of the node structure. > - Not used for types or decls. */ > - > -#define DEFTREECODE(SYM, NAME, TYPE, LENGTH) LENGTH, > -#define END_OF_BASE_TREE_CODES 0, > - > -const unsigned char tree_code_length[] = { > -#include "all-tree.def" > -}; > - > -#undef DEFTREECODE > -#undef END_OF_BASE_TREE_CODES > > /* Names of tree components. > Used for printing out the tree and error messages. */ > -- > 2.17.1 > >