Right now there is no documentation for the GCC tree -> rtl interfaces (or more generally the interfaces for adding new languages). Such documentation would be of great benefit to the project. Until such time as we can formally start documenting the interface this file will serve as a repository for information on these interface and any incompatible changes we've made. 2004-09-09: In an effort to decrease execution time, single char tree code classes were changed to enumerated values. Old way: DEFTREECODE (CLASS_METHOD_DECL, "class_method_decl", 'd', 0) New way: DEFTREECODE (CLASS_METHOD_DECL, "class_method_decl", tcc_declaration, 0) 2001-02-26: A DECL_INITIAL of NULL_TREE or error_mark_node in a VAR_DECL is no longer taken to signify a tentative definition which should not be emitted until end-of-file. Frontends which want that behavior should set DECL_DEFER_OUTPUT before calling rest_of_decl_compilation. Feb 1, 1998: GCC used to store structure sizes & offsets to elements as bitsize quantities. This causes problems because a structure can only be (target memsize / 8) bytes long (this may effect arrays too). This is particularly problematical on machines with small address spaces. So: All trees that represent sizes in bits should have a TREE_TYPE of bitsizetype (rather than sizetype). Accordingly, when such values are computed / initialized, care has to be takes to use / compute the proper type. When a size in bits is converted into a size in bytes, which is expressed in trees, care should be taken to change the tree's type again to sizetype. ?? 1997: In an effort to decrease cache thrashing and useless loads we've changed the third argument to the DEFTREECODE macro to be a single char. This will affect languages that defined their own tree codes (usually in a .def file). Old way: DEFTREECODE (CLASS_METHOD_DECL, "class_method_decl", "d", 0) New way: DEFTREECODE (CLASS_METHOD_DECL, "class_method_decl", 'd', 0) Copyright (C) 1998-2014 Free Software Foundation, Inc. Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved.