02 February 2016

Nuitka Release 0.5.19

This is to inform you about the new stable release of Nuitka. It is the extremely compatible Python compiler, “download now”.

This release brings optimization improvements for dictionary using code. This is now lowering subscripts to dictionary accesses where possible and adds new code generation for known dictionary values. Besides this there is the usual range of bug fixes.

Bug Fixes

Fix, attribute assignments or deletions where the assigned value or the attribute source was statically raising crashed the compiler.
Fix, the order of evaluation during optimization was considered in the wrong order for attribute assignments source and value.
Windows: Fix, when g++ is the path, it was not used automatically, but now it is.
Windows: Detect the 32 bits variant of MinGW64 too.
Python3.4: The finalize of compiled generators could corrupt reference counts for shared generator objects. Fixed in 0.5.18.1 already.
Python3.5: The finalize of compiled coroutines could corrupt reference counts for shared generator objects.

Optimization

When a variable is known to have dictionary shape (assigned from a constant value, result of dict built-in, or a general dictionary creation), or the branch merge thereof, we lower subscripts from expecting mapping nodes to dictionary specific nodes. These generate more efficient code, and some are then known to not raise an exception.
```
def someFunction(a, b):
    value = {a: b}
    value["c"] = 1
    return value
```
The above function is not yet fully optimized (dictionary key/value tracing is not yet finished), however it at least knows that no exception can raise from assigning value["c"] anymore and creates more efficient code for the typical result = {} functions.
The use of “logical” sharing during optimization has been replaced with checks for actual sharing. So closure variables that were written to in dead code no longer inhibit optimization of the then no more shared local variable.
Global variable traces are now faster to decide definite writes without need to check traces for this each time.

Cleanups

No more using “logical sharing” allowed to remove that function entirely.
Using “technical sharing” less often for decisions during optimization and instead rely more often on proper variable registry.
Connected variables with their global variable trace statically avoid the need to check in variable registry for it.
Removed old and mostly unused “assume unclear locals” indications, we use global variable traces for this now.

Summary

This release aimed at dictionary tracing. As a first step, the value assign is now traced to have a dictionary shape, and this this then used to lower the operations which used to be normal subscript operations to mapping, but now can be more specific.

Making use of the dictionary values knowledge, tracing keys and values is not yet inside the scope, but expected to follow. We got the first signs of type inference here, but to really take advantage, more specific shape tracing will be needed.

Nuitka Progress in 2015 Nuitka Release 0.5.20