Szathmáry László honlapja @ DEIK | Nim2 / Compilation 🤖

The Nim compiler doesn't produce an executable binary directly. Instead, first it compiles to C, and then this C code is compiled with the platform's C compiler (under Linux it's typically the GCC, but you can also use Clang, or some other C compiler). Nim also supports other targets: C++, JavaScript. However, most often we'll use the C backend.

The intermediate C code is hidden, and the invokation of the C compiler is also hidden by the Nim compiler. You don't have to deal with the C code, it's managed in the background by the Nim compiler.

You'll only see this: [Nim source code] → [Nim compiler] → [runnable EXE]

$ nim c prg.nim

𝥶Compiles the program in debug mode. Faster compilation, slower EXE.

$ nim c -d:release prg.nim

𝥶Compiles the program in release mode. Slower compilation, fast EXE. The EXE is smaller.

Silent compilation 🫢

By default, the nim compiler gives some feedback about what it's doing. If you don't need this info, you can switch it off:

$ nim c --hints:off --warnings:off prg.nim

Create a fast EXE ⚡

Here is how you can optimize for speed:

$ nim c -d:release --opt:speed prg.nim

On Linux, there's a high chance that the default C compiler is GCC. Sometimes, Clang produces faster EXEs. You can also try that:

$ nim c --cc:clang -d:release prg.nim

$ nim c --cc:clang -d:release --opt:speed prg.nim

Create a small EXE 🤏

I took the same program and compiled it with different options. File sizes are indicated.

$ nim c prg.nim                                              # 98336 bytes

$ nim c -d:release prg.nim                                   # 69288 bytes

$ nim c -d:release --opt:size prg.nim                        # 38168 bytes

$ nim c -d:release --opt:size --passL:-s prg.nim             # 27120 bytes

$ nim c -d:release --opt:size -d:quick --passL:-s prg.nim    # 26912 bytes

"--passL:-s" calls "strip -s"

Applying UPX 📦

If you want to further minimize the size of the binary, you can also experiment with upx. Take the smallest binary and try these:

$ upx <binary>           # fast; good compression

$ upx --best <binary>    # better compression

$ upx --lzma <binary>    # even better than "--best" :)

After UPX, always try the EXE to check if it still works.

Links 🔗

Nim Compiler User Guide