Programming Languages - Compilers and Runtimes

runtime: some languages have big runtimes, or full virtual machines, like Java (JVM); some languages have small runtimes, just a library to provide critical functions, like libc for C, and runtime lib for Go.
GC refers to runtime GC; Swift has Automatic Reference Counting but at the compile time.
In Go, GC is provided by the runtime library; while in Java / JavaScript, GC is provided by the virtual machine (JVM / V8).

VMs

JVM (Java Virtual Machine): Java, Scala, Groovy, Kotlin
- Why Groovy is more Popular than Scala: Groovy is 100% Java compatible because it IS Java; take any Java class, change the extension to from '.java' to '.groovy' and it WILL compile (NOTE: one must have groovy library installed).
CLR (Common Language Runtime): C#
HHVM (HipHop Virtual Machine): PHP/Hack. HHVM JIT compilation, executed PHP or Hack code is first transformed into intermediate HipHop bytecode (HHBC), which is then dynamically translated into x86-64 machine code, optimized, and natively executed. This contrasts with PHP's usual interpreted execution, in which the Zend Engine transforms PHP source code into opcodes that serve as a form of bytecode, and executes the opcodes directly on the Zend Engine's virtual CPU.

LLVM is the backend AND the umbrella project name.
LLVM is NOT a traditional virtual machine.
It is NOT an acronym (though originally it stands for Low Level Virtual Machine).
It contains modularized compiler components and tool chains.
Clang: frontend for C/C++/Object-C/Object-C++.
Backend converts the LLVM Intermediate Representation (IR) to code for a specified machine or other languages (hardware OR software target)
https://llvm.org
Emscripten: an LLVM/Clang-based compiler that compiles C and C++ source code to WebAssembly.
rustc, translates Rust code into low-level LLVM IR.
performance-critical code is usually build with LLVM-based toolchains.

2 Primary C/C++ compilers: Clang and GCC.

Notes:

Clang was originated from Apple but now widely used (You will find Google, Facebook Microsoft, Intel, Qualcomm, Huawei in LLVM Found ation sponsor list https://foundation.llvm.org/docs/sponsors/)
Emerging languages are using the LLVM frameworks, such as Swift, Rust.
GCC was deprecated in Android in 2019 and removed in 2020
GCC is the official compiler for the GNU and Linux systems
Clang supports a wide variety of C standard library implementations.

Conclusion: use Clang/LLVM if you do not have to use GCC.

On Debian / Ubuntu:

$ sudo apt install clang libc++-dev libc++abi-dev

Verify:

$ clang --version
clang version xx.x.x
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

A typescript / javascript compiler, written in Rust. (https://swc.rs/)

Used by tools like Next.js, Parcel, and Deno.

static compiler, or ahead-of-time(AOT) compiler: at compile-time, e.g. from .java to bytecode .class.
dynamic compiler, or just-in-time(JIT) compiler: at run-time, e.g. in Java, compiles bytecode to native instructions.

bytecode is portable, but native code is not.

Java JIT 2 flavors:

client-side compiler(with -client option): fewer resources, sensitive to startup time.
server-side compiler(with -server option): long running, more advanced optimizations.

Besides Java, PyPy provides JIT for Python, V8 compiles javascript directly to native machine code.

A script is program code that doesn’t need pre-processing (e.g. compiling) before being run.