https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111020
--- Comment #2 from H. Peter Anvin <hpa at zytor dot com> --- Named subsets are, inherently, designed to make sense toward mass-produced products where the hardware and software are designed (mostly) independently. However, what I mean with "very deep embedded use" is hardware and software being co-designed. The RISC-V ISA policy is that those are considered vendor-specific subsets and are to be given an X* name; however, gcc obviously needs to be able to understand the meaning of this X* name. At this point there is no way to do without changing the source code in nontrivial ways. Regardless of if it is done in source code or at runtime, by implementing a fine-grained, preferably table-driven, approach to subsets in gcc then it would be very simple for a hardware implementor to define their custom X-subsets without a lot of surgery to the code, *and* it makes it possible to take it one step further and allowing custom (or newly defined! - there have been multiple instances already of new subsets of existing instructions defined a posteori) instruction subsets to be defined in a configuration file.
