When building a compiler for a high-level language, certain intrinsic features of the language must be expressed in terms of the resulting low-level operations. Complex features are often expressed by explicitly weaving together bits of low-level IR, a process that is tedious, error prone, difficult to read, difficult to reason about, and machine dependent. In the Graal compiler for Java, we take a different approach: we use snippets of Java code to express semantics in a high-level, architecture-independent way. Two important restrictions make snippets feasible in practice: they are compiler specific, and they are explicitly prepared and specialized. Snippets make Graal simpler and more portable while still capable of generating machine code that can compete with other compilers of the Java HotSpot VM.

We present a JVM prototype implemented in the purely-functional language Haskell. It exploits several features of the language, such as strong static typing to implement an intermediate representation, and abstraction mechanism to express machine code generation in the manner of a domain specific language.The compiler consists of (i) a pass to transform Java bytecode to a register-based intermediate representation, (ii) application of an existing data-flow analysis framework to our intermediate representation and (iii) machine code generation that targets the x86 architecture. The implementation follows a compile-only approach. To implement certain Java features efficiently, code patching is used.Various code samples demonstrate the elegance of our prototype. Results prove reasonable performance compared to realworld implementations.