i could easily google it but, what's LLVM? (me googling it would not translate automatically into me writing up an answer for everybody, however, LLVM seems to be the name of a project that includes clang)
LLVM is a series of projects, of which the core project is an assembly-like language (more specifically a compiler IR (or five)), optimization passes for said language, code generators to convert it to several major assembly languages (or their machine code representation), and a few associated tools that are similar to things provided by GNU binutils.
Other projects are included in LLVM. Clang is the C/C++ compiler. There is a C standard library, an OpenCL standard library, a C++ standard library (all inventively named lib<language>). There is also a library to support compiler builtins called compiler-rt, and a library to support OpenMP called openmp, and an implementation of C++ parallel executors in pstl. There is also a linker (lld) and a debugger (lldb). There is also a machine code optimizer called bolt, and yet another compiler framework called MLIR. Finally, there are several different Fortran compilers all called flang (don't ask).
LLVM is also notably used as the compiler backend for Rust, Swift and (I think) Zig and more. Rust is as fast as C because llvm includes all the optimizations used to make C programs fast, and rust gets to reuse all of those optimizations. Llvm can compile working binaries for all modern platforms (windows, Mac, Linux, FreeBSD, iOS, android, etc) and basically all modern architectures (x86, arm, riscv, wasm, etc). It’s also the official compiler toolchain used by Apple on all their platforms (and apple fund a lot of llvm development). I think Google also uses it for their C/C++ code and some Linux distributions use llvm instead of gcc as a compiler toolchain.
Llvm is everywhere. There’s a good chance llvm compiled some or all of the software you’re using to read this comment.
