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Why no bytecode format?

A compiled script, a TdwsProgram, cannot be saved to a file, and will not ever be. Why is that?

This is a question that dates back to the first DWS, as it was re-asked recently, I will expose the rationale here.

How fast is the DWS compiler?

I did some quick benchmarking against PascalScript and Delphi itself.
I generated a script based on the following template:

var myvar : Integer;

The assignment line being there only once, 100 times, 1000 times, etc. The result was saved to a file, and the benchmark consisted in loading the file, compiling and then running it for DWS. For PascalScript, the times are broken down into compiling, loading the bytecode output from a file, and then running that bytecode. Disk size indicates the size of the generated bytecode.
All times are in milliseconds (and have been updated, see Post-Scriptum below):


For line counts expected for typical scripts (less than 1000), compared to PascalScript, the cost of not being able to save to a bytecode is a one-time hit in the sub-15 milliseconds range, on the first run.
This illustrates why it is not really worth the trouble maintaining a bytecode version for scripting purposes, and that is also my practical experience.

For larger scripts, it is expected the execution complexity will dwarf the compile time: the benchmark code tested here doesn’t have any loops, anything more real-life will have loops, and will likely have a greater runtime/compiletime ratio.

What of Delphi?

For reference, I tried compiling the larger line counts versions with Delphi XE, from the IDE.

What else? The DWS compiler has an initial setup cost higher than PascalScript, but as code size grows, it starts pulling ahead. That setup overhead will nevertheless bear some investigation 😉.
Once compiled, the 10x execution speed ratio advantage of DWS vs PascalScript is consistent with other informal benchmarks.


Gave a quick look at the setup overhead with SamplingProfiler [2], and found two bottlenecks/bugs. The outcome was the shaving off of 3 ms from the DWS compile times, ie. the compile times for the 1, 100 and 1000 lines cases are now 0.95 ms, 2.85 ms and 19.1 ms respectively.