On Thu, Jan 26, 2023 at 09:45:35AM -0500, Patrick Palka via Gcc-patches wrote:
> > +#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?
And I'd argue with the tiny bit.
In my x86_64-linux cc1plus from today, I see 193 _ZL16tree_code_length vars,
374 bytes each, and 324 _ZL14tree_code_type vars, 1496 bytes each.
So, that means waste of 555016 .rodata bytes, plus being highly non-cache
friendly.
The following patch does that.
So far tested on x86_64-linux in my -O0 working tree (system gcc 12
compiler) where .rodata shrunk with the patch by 928896 bytes, in last
stage of a bootstrapped tree (built by today's prev-gcc) where .rodata
shrunk by 561728 bytes (in neither case .text or most other sections
changed sizes) and on powerpc64le-linux --disable-bootstrap
(system gcc 4.8.5) to test also the non-C++17 case.
Ok for trunk if it passes full bootstrap/regtest?
BTW, wonder if tree_code_type couldn't be an array of unsigned char
elements rather than enum tree_code_class and we'd then cast it
to the enum in the macro, that would shrink that array from 1496 bytes
to 374. Of course, that sounds like stage1 material.
2023-01-26 Patrick Palka <ppa...@redhat.com>
Jakub Jelinek <ja...@redhat.com>
* tree-core.h (tree_code_type, tree_code_length): For
C++17 and later, add inline keyword, otherwise don't define
the arrays, but declare extern arrays.
* tree.cc (tree_code_type, tree_code_length): Define these
arrays for C++14 and older.
--- gcc/tree-core.h.jj 2023-01-02 09:32:31.188158094 +0100
+++ gcc/tree-core.h 2023-01-26 16:02:34.212113251 +0100
@@ -2284,17 +2284,20 @@ struct floatn_type_info {
/* Matrix describing the structures contained in a given tree code. */
extern bool tree_contains_struct[MAX_TREE_CODES][64];
+/* Class of tree given its code. */
+#if __cpp_inline_variables >= 201606L
#define DEFTREECODE(SYM, NAME, TYPE, LENGTH) TYPE,
#define END_OF_BASE_TREE_CODES tcc_exceptional,
-
-/* Class of tree given its code. */
-constexpr enum tree_code_class tree_code_type[] = {
+constexpr inline enum tree_code_class tree_code_type[] = {
#include "all-tree.def"
};
#undef DEFTREECODE
#undef END_OF_BASE_TREE_CODES
+#else
+extern const enum tree_code_class tree_code_type[];
+#endif
/* Each tree code class has an associated string representation.
These must correspond to the tree_code_class entries. */
@@ -2302,14 +2305,18 @@ extern const char *const tree_code_class
/* Number of argument-words in each kind of tree-node. */
+#if __cpp_inline_variables >= 201606L
#define DEFTREECODE(SYM, NAME, TYPE, LENGTH) LENGTH,
#define END_OF_BASE_TREE_CODES 0,
-constexpr unsigned char tree_code_length[] = {
+constexpr inline unsigned char tree_code_length[] = {
#include "all-tree.def"
};
#undef DEFTREECODE
#undef END_OF_BASE_TREE_CODES
+#else
+extern const unsigned char tree_code_length[];
+#endif
/* Vector of all alias pairs for global symbols. */
extern GTY(()) vec<alias_pair, va_gc> *alias_pairs;
--- gcc/tree.cc.jj 2023-01-13 17:37:45.259482663 +0100
+++ gcc/tree.cc 2023-01-26 16:03:59.796878082 +0100
@@ -74,7 +74,33 @@ along with GCC; see the file COPYING3.
#include "asan.h"
#include "ubsan.h"
+#if __cpp_inline_variables < 201606L
+/* 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
+#endif
/* Names of tree components.
Used for printing out the tree and error messages. */
Jakub
