According to MSVC manual (*1), cl.exe can skip including a header file
when that:
- contains #pragma once, or
- starts with #ifndef, or
- starts with #if ! defined.
GCC has a similar trick (*2), but it acts more stricter (e. g. there
must be _no tokens_ outside of #ifndef...#endif).
Sun C lacked #pragma once for a looong time. Oracle Developer Studio
12.5 finally implemented it, but we cannot assume such recent version.
This changeset modifies header files so that each of them include
strictly one #ifndef...#endif. I believe this is the most portable way
to trigger compiler optimizations. [Bug #16770]
*1: https://docs.microsoft.com/en-us/cpp/preprocessor/once
*2: https://gcc.gnu.org/onlinedocs/cppinternals/Guard-Macros.html
* include/ruby/ruby.h (struct RClass): add super, remove iv_index_tbl.
since RCLASS_SUPER() is commonly used inside while loops, we move it
back inside struct RClass to improve cache hits. this provides a
small improvement (1%) in hotspots like rb_obj_is_kind_of()
* internal.h (struct rb_classext_struct): remove super, add
iv_index_table
* internal.h (RCLASS_SUPER): update for new location
* internal.h (RCLASS_SET_SUPER): ditto
* internal.h (RCLASS_IV_INDEX_TBL): ditto
* object.c (rb_class_get_superclass): ditto
* include/ruby/backward/classext.h (RCLASS_SUPER): ditto
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44294 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
