On Fri, 27 Jan 2023, Jakub Jelinek wrote:
> On Fri, Jan 27, 2023 at 07:42:39AM +0000, Richard Biener wrote:
> > > 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.
> >
> > One could argue the same way for this patch (and instead revert),
>
> Well, this patch is in fact a conditional reversion (revert for
> C++11/14, add one keyword to 2 declarations otherwise).
>
> > I'd say if we tweak this now then tweak it to the maximum extent?
> > Isn't sth like 'enum unsigned char tree_code_class' now possible?
> > (and a static assert the enum values all fit, though that would
> > be diagnosed anyway?)
>
> C++11 indeed has
> enum tree_code_class : unsigned char {
> tcc_exceptional,
> ...
> tcc_expression
> };
> and one indeed gets an error if some enumerator doesn't fit.
> The problem I see with this is that the type is 8-bit everywhere,
> which I'd be afraid could cause worse code generation (of course,
> one would need to try to see how much; e.g. build the compiler
> unmodified, with the unsigned char array plus explicit casts from
> the array and finally with unsigned char as underlying type).
> When passing around enum tree_code_class etc., it is fine if it
> is 32-bit. And there isn't a way to create an enum with different
> underlying type but with the same enumerators as in another enum.
> Perhaps for tree_code_class we could away with the underlying type
> because it is mostly used in the macros which immediately compare
> it, in gcc/*.cc just in the following explicitly:
> expr.cc:get_def_for_expr_class (tree name, enum tree_code_class tclass)
> fold-const.cc: enum tree_code_class tclass;
> fold-const.cc: enum tree_code_class tclass = TREE_CODE_CLASS (code);
> fold-const.cc: enum tree_code_class tclass = TREE_CODE_CLASS (code);
> fold-const.cc: enum tree_code_class kind = TREE_CODE_CLASS (code);
> fold-const.cc: enum tree_code_class kind = TREE_CODE_CLASS (code);
> fold-const.cc: enum tree_code_class kind = TREE_CODE_CLASS (code);
> fold-const.cc: enum tree_code_class kind = TREE_CODE_CLASS (code);
> gimple-fold.cc: enum tree_code_class kind = TREE_CODE_CLASS
> (subcode);
> print-tree.cc: enum tree_code_class tclass;
> print-tree.cc: enum tree_code_class tclass;
> tree.cc: These must correspond to the tree_code_class entries. */
> tree.cc:const char *const tree_code_class_strings[] =
> tree.cc: enum tree_code_class type = TREE_CODE_CLASS (code);
> tree.cc: enum tree_code_class type = TREE_CODE_CLASS (code);
> tree.cc:tree_class_check_failed (const_tree node, const enum tree_code_class
> cl,
> tree.cc:tree_not_class_check_failed (const_tree node, const enum
> tree_code_class cl,
> tree.cc: const enum tree_code_class c = TREE_CODE_CLASS (TREE_CODE (t));
> tree.cc: const enum tree_code_class c = TREE_CODE_CLASS (TREE_CODE (t));
> tree-dump.cc: enum tree_code_class code_class;
> tree-inline.cc: enum tree_code_class cl = TREE_CODE_CLASS (code);
> tree-pretty-print.cc: enum tree_code_class tclass;
> tree-ssa-live.cc: enum tree_code_class c = TREE_CODE_CLASS (TREE_CODE (t));
> tree-ssa-operands.cc: enum tree_code_class codeclass;
> But as I said, one would need to watch for code generation at least on
> a couple of common hosts, and while x86_64 should be one of them, it might
> have bigger effects on others as x86 has byte comparison etc. instructions.
Hm, yes. Not sure if using uint_fast8_t would make a difference where
it should. So lets keep this change separate.
Richard.
> >
> > > 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"
> > > };
> >
> > Do we need an explicit external definition somewhere when
> > constant folding isn't possible?
>
> >
> > Otherwise looks good to me.
> >
> > Thanks,
> > Richard.
> >
> > > #undef DEFTREECODE
> > > #undef END_OF_BASE_TREE_CODES
> > > +#else
> > > +extern const enum tree_code_class tree_code_type[];
>
> There is one here for the C++11 and C++14 cases.
> For C++17 and later it isn't needed,
> constexpr inline enum tree_code_class tree_code_type[] = {
> ...
> };
> means this is a comdat variable in all TUs which need non-ODR
> uses of it (tree_code_type[23] evaluates to constant expression,
> but tree_code_type[x] or &tree_code_type[23] etc. often don't and then
> the comdat var is emitted and all TUs share one copy of the variable.
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
