I'm working on readying the Toshiba Media Processor (mep-elf) port for contribution to GCC 4.x, but we added some core changes needed to support it. The changes are listed below; I'd like some feedback about these before I go too far with them. Are these concepts acceptable for inclusion in gcc?
Coprocessor types - the MeP chip has optional coprocessors, each with their own register sets. They need their own internal types (mostly to keep track of which unit to use), which we've created by prefixing the existing types with COP (i.e. COPSImode, COPDFmode, etc). This affects the generators, some MI files, etc. The types don't exist unless the target calls for them. The CPU supports two operation modes - core and vliw. To properly manage inlining, we need target hooks for when function A can inline function B (both functions' attributes need to be inspected), and for calls that are semantically disallowed (i.e. functions can't call other-mode static inline functions). The core and vliw modes have different instructions, and it's expected that users of this port will make heavy use of intrinsics and asms, so even tree-level inlining needs to be managed. The number of registers available to GCC varies with the coprocessor choice, via pragmas in a sysroot-wide header file. Thus, we need hooks that let us modify (or at least re-calculate) gcc's internal tables (i.e. call init_reg_sets_1 et all, during pragma handling). Also, we need access to reg_class_subclasses[], which was hidden a while back. We added a validate_replace_rtx_subexp() which is like validate_replace_rtx() but only does the replacement on a sub-expression of the insn. There's a chip-specific optimization that uses this, we didn't want to have to recompute it ourselves.
