The compiler plugin and code generator¶
Compilation to native code happens in two steps. First, Scala code is compiled
into Native Intermediate Representation by nscplugin, the Scala compiler plugin. It runs as one of the
later phases of the Scala compiler and inspects the AST and generates
files. Finally, the
.nir files are compiled into
.ll files and passed
to LLVM by the native compiler.
Tips for working on the compiler¶
When adding a new intrinsic, the first thing to check is how clang would compile
it in C. Write a small program with the behavior you are trying to add and
compile it to
clang -S -emit-llvm foo.c
Now write the equivalent Scala code for the new intrinsic in the sandbox project. This project contains a minimal amount of code and has all the toolchain set up which makes it fast to iterate and inspect the output of the compilation.
To compile the sandbox project run the following in the sbt shell:
If the example code for the new intrinsic requires you to change APIs in
then remember to also publish the changes with
After compiling the sandbox project you can inspect the
.ll files inside
sandbox/target/scala-<version>/ll. The files are grouped by the package name.
By default the
Test.scala file doesn’t define a package, so the resulting file
__empty.ll. Locating the code you are interested in might require that
you get more familiar with the LLVM assembly language.
When working on the compile plugin you’ll need to publish it and reload each time you want to recompile the sandbox project. This can be achieved with:
Certain intrinsics might require adding new primitives to the compiler plugin.
This can be done in
NirPrimitives with an accompanying definition in
NirDefinitions. Ensure that new primitives are correctly registered.
The NIR code generation uses a builder to maintain the generated instructions. This allows to inspect the instructions before and after the part of the compilation you are working on has generated code.