Smalltalk is a dynamic and reflective programming language that allows developers to dynamically modify and extend the behavior of objects at runtime. Smalltalk has a standard compiler that translates Smalltalk code into bytecode, which is then executed by the Smalltalk virtual machine.

In addition to the standard Smalltalk language features, some Smalltalk implementations provide compiler-specific extensions that enhance the language with additional functionality and optimizations. These extensions are often specific to a particular implementation and may not be available in other Smalltalk environments.

In this blog post, we will explore some of the most common compiler-specific extensions found in Smalltalk implementations.

1. Method Inlining

Method inlining is a compiler optimization technique that replaces a method call with the actual code of the method being called. This optimization improves performance by avoiding the overhead of method invocation.

In Smalltalk, certain implementations provide the ability to inline methods directly into the calling context. This is particularly useful for frequently called methods or methods with critical performance requirements.

To enable method inlining, developers can use the inline: pragma in the method declaration:

myMethod
    <inline: true>
    "Method implementation goes here"

By specifying inline: true, the compiler will attempt to inline myMethod whenever possible, resulting in faster execution.

2. JIT Compilation

Just-in-Time (JIT) compilation is a technique used by some Smalltalk implementations to improve execution performance. Rather than interpreting Smalltalk bytecode, JIT compilers translate bytecode into native machine code at runtime for direct execution by the processor.

JIT compilers can perform various optimizations such as method inlining, loop unrolling, and dynamic code generation. These optimizations significantly improve the performance of Smalltalk programs.

One commonly used JIT compiler for Smalltalk is the Cog VM (Virtual Machine), which is available in implementations like Squeak and Pharo. Cog VM utilizes a combination of interpreter and JIT compilation techniques to provide high-performance execution.

To take advantage of JIT compilation, developers can simply use an implementation that includes a JIT compiler, such as Squeak or Pharo.

Conclusion

Compiler-specific extensions in Smalltalk implementations provide valuable optimizations and additional functionality beyond the standard language features. Method inlining and JIT compilation are two examples of such extensions that can greatly improve the performance of Smalltalk programs.

When using these extensions, it’s important to consider their compatibility across different Smalltalk implementations. While some extensions are portable, others are specific to particular environments or virtual machines.

To achieve the best performance and compatibility, it is recommended to thoroughly understand the capabilities and limitations of the Smalltalk implementation being used.