| # Lightening | |
| Lightening is a just-in-time code generation library derived from GNU | |
| Lightning, adapted to the purposes of the GNU Guile project. | |
| ## Use | |
| ``` | |
| gcc -flto -O2 -g -o lightening.o -c lightening/lightening.c | |
| gcc -flto -O2 -g -o my-program lightening.o my-program.c | |
| ``` | |
| See the GNU Lightning manual for more on how to program against | |
| Lightening (much of the details are the same). | |
| ## What's the difference with GNU Lightning? | |
| This project is called Lightening because it's lighter-weight than GNU | |
| Lightning. When you go to generate code at run-time with GNU Lightning, | |
| what happens is that you build up a graph of nodes which GNU Lightning | |
| "optimizes" before finally emitting machine code. These optimizations | |
| can improve register allocation around call sites. However they are not | |
| helpful from a Guile perspective, as they get in the way of register | |
| allocation that we need to do; and they actually prevent access to all | |
| the registers that we would like to have. | |
| Guile needs a simple, light-weight code generation library. The GNU | |
| Lightning architecture-specific backends provide the bulk of this | |
| functionality, and Lightening wraps it all in a lightweight API. | |
| ## Supported targets | |
| Lightening can generate code for the x86-64, i686, ARMv7, and AArch64 | |
| architectures. It supports the calling conventions of MS Windows, | |
| GNU/Linux, and Mac OS. | |
| On i686, Lightening requires SSE support. On ARMv7, we require hardware | |
| floating-point support (the VFP instructions), as well as the UDIV/SDIV | |
| instructions. | |
| Lightening is automatically tested using GitLab's continuous integration | |
| for under the supported architectures, for GNU/Linux; for a list of | |
| recent jobs, see [the CI | |
| page](https://gitlab.com/wingo/lightening/-/jobs). | |
| ## Future targets | |
| Lightening has some inherited code from GNU Lightning for MIPS, PPC64, | |
| and s390. Patches to adapt this code to the Lightening code structure | |
| are quite welcome. | |
| RISC-V support would be fun too. | |
| ## Status | |
| Lightening is used in GNU Guile since version 2.9.2 and seems to work | |
| well. | |