Add support for custom data types mapped to custom load/store instructions in GCC RISC-V backend

[NAbuShaibeh]

Hello,

I am extending the RISC-V GNU toolchain to add a new memory handling mechanism that requires the compiler to use custom load and store instructions for specific variables allocated in a particular memory region.

Context

I’ve implemented a set of custom load/store instructions in the RISC-V backend and verified that the assembler and simulator recognize them.
The next step is to connect these instructions with certain variable types or attributes so that when such variables are accessed in C/C++ source code, the compiler automatically emits the corresponding custom load/store instructions instead of the standard ones.

In addition, these variables should be allocated in a dedicated data section (for example, .custom_data) that the linker maps to a defined region in memory.

Goal
I’d like to integrate this feature cleanly into GCC so that:

• Variables annotated with a specific attribute (or type) use the custom load/store instructions.
• These variables are automatically placed in a designated section (e.g. .custom_data).
• The compiler enforces simple separation between normal variables and those requiring the custom memory access instructions.

Questions

• Which GCC front-end and back-end source files are best suited for implementing such type- or attribute-based instruction selection?
• Is there an existing mechanism (target hooks, machine attributes, or storage class specifiers) that could support this use case without fully introducing a new data type?
• Are there examples of other GCC targets that implement specialized load/store paths for non-standard memory regions?

Thanks in advance for your help and time!

[TommyMurphyTM1234]

• Which GCC front-end and back-end source files are best suited for implementing such type- or attribute-based instruction selection?

You should read the GCC Internals documentation to better understand how to approach customising the GCC toolchain:

• https://gcc.gnu.org/onlinedocs/gccint/

You may also need to understand the internals of some of the Binutils tools:

• https://sourceware.org/binutils/binutils-porting-guide.txt

There are also several existing open and closed issues and PRs in this repo that touch on issues relating to this topic.

You might also get better feedback on upstream GCC forums such as the mailing lists especially since your query is really about customising the GCC toolchain and isn't really a RISC-V or riscv-gnu-toolchain specific.

• https://gcc.gnu.org/lists.html