Low Level Virtual Machine (LLVM) is:

A compilation strategy designed to enable effective program optimization across
the entire lifetime of a program. LLVM supports effective optimization at
compile time, link-time (particularly interprocedural), run-time and offline
(i.e., after software is installed), while remaining transparent to developers
and maintaining compatibility with existing build scripts.

A virtual instruction set - LLVM is a low-level object code representation that
uses simple RISC-like instructions, but provides rich, language-independent,
type information and dataflow (SSA) information about operands. This combination
enables sophisticated transformations on object code, while remaining
light-weight enough to be attached to the executable. This combination is key to
allowing link-time, run-time, and offline transformations.

A compiler infrastructure - LLVM is also a collection of source code that
implements the language and compilation strategy. The primary components of the
LLVM infrastructure are the C & C++ front-end, a link-time optimization
framework with a growing set of global and interprocedural analyses and
transformations, static back-ends for the X86, X86-64, PowerPC 32/64, ARM,
Thumb, IA-64 and SPARC architectures, a back-end which emits portable C
code, and a Just-In-Time compiler for X86, X86-64, PowerPC 32/64 processors.

Homepage:
https://llvm.org/
