Re: [PATCH] tree: Fix up tree_code_{length,type}

[Richard Biener <rguenther@suse.de>]

> Am 27.01.2023 um 13:41 schrieb Patrick Palka via Gcc-patches <gcc-patches@gcc.gnu.org>:
> 
> On Thu, 26 Jan 2023, Patrick Palka wrote:
> 
>>> On Thu, 26 Jan 2023, Jakub Jelinek wrote:
>>> 
>>> 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.
>> 
>> LGTM FWIW.  On a related note I noticed the function
>> tree.h:tree_operand_length is declared static and is then used in the
>> non-static inline functions tree_operand_check etc, which seems to be
>> also be a (harmless) ODR violation?
>> 
>> We probably should do s/static inline/inline throughout the header files
>> at some point, which'd hopefully reduce the size of and speed up stage1
>> cc1plus.
> 
> Mechanically replacing uses of static inline in headers via
> 
>  echo gcc/*.h gcc/*/*.h | xargs sed -i 's/^static inline/inline/g'
> 
> reduces rodata size of stage1 cc1plus by ~1.5MB and seems to make it ~2%
> faster.  Not bad..

Nice.

Richard 


>> 
>>> 
>>> 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  <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.
>>> 
>>> --- 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
>>> 
>>> 
>> 
>