[gcc r13-5431] tree: Fix up tree_code_{length,type}

[gcc r13-5431] tree: Fix up tree_code_{length,type}

[Jakub Jelinek]

https://gcc.gnu.org/g:b0241ce6e37031e1cbde73d5389ec7f1d063e099

commit r13-5431-gb0241ce6e37031e1cbde73d5389ec7f1d063e099
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Jan 27 10:51:35 2023 +0100

    tree: Fix up tree_code_{length,type}
    
    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.
    
    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 plus with
    fully x86_64-linux, i686-linux and powerpc64le-linux bootstraps/regtests.
    
    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.
    
    2023-01-27  Patrick Palka  <ppalka@redhat.com>
                Jakub Jelinek  <jakub@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.

Diff:
---
 gcc/tree-core.h | 15 +++++++++++----
 gcc/tree.cc     | 26 ++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index 8124a1328d4..acd8deea34e 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -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_strings[];
 
 /* 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;
diff --git a/gcc/tree.cc b/gcc/tree.cc
index 7473912a065..952bbece8cd 100644
--- a/gcc/tree.cc
+++ b/gcc/tree.cc
@@ -74,7 +74,33 @@ along with GCC; see the file COPYING3.  If not see
 #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.  */