Nuitka Release 0.5.23

This is to inform you about the new stable release of Nuitka. It is the extremely compatible Python compiler. Please see the page "What is Nuitka?" for an overview.

This release is focusing on optimization, the most significant part for the users being enhanced scalability due to memory usage, but also break through structural improvements for static analysis of iterators and the debut of type shapes and value shapes, giving way to "shape tracing".

Bug Fixes

  • Fix support Python 3.5.2 coroutine changes. The checks got added for improved mode for older 3.5.x, the new protocol is only supported when run with that version or higher.

  • Fix, was falsely optimizing away unused iterations for non-iterable compile time constants.

    iter(1) # needs to raise.
    
  • Python3: Fix, eval must not attempt to strip memoryviews. The was preventing it from working with that type.

  • Fix, calling type without any arguments was crashing the compiler. Also the exception raised for anything but 1 or 3 arguments was claiming that only 3 arguments were allowed, which is not the compatible thing.

  • Python3.5: Fix, follow enhanced error checking for complex call handling of star arguments.

  • Compatibility: The from x import x, y re-formulation was doing two __import__ calls instead of re-using the module value.

Optimization

  • Uses only about 66% of the memory compared to last release, which is very important step for scalability independent of re-loading. This was achieved by making sure to break loop traces and their reference cycle when they become unused.

  • Properly detect the len of multiplications at compile time from newly introduces value shapes, so that this is e.g. statically optimized.

    print(len("*" * 10000000000))
    
  • Due to newly introduced type shapes, len and iter now properly detect more often if values will raise or not, and warn about detected raises.

    iter(len((something)) # Will always raise
    
  • Due to newly introduced "iterator tracing", we can now properly detect if the length of an unpacking matches its source or not. This allows to remove the check of the generic re-formulations of unpackings at compile time.

    a, b = b, a    # Will never raise due to unpacking
    a, b = b, a, c # Will always raise, 3 items cannot unpack to 2
    
  • Added support for optimization of the xrange built-in for Python2.

  • Python2: Added support for xrange iterable constant values, pre-building those constants ahead of time.

  • Python3: Added support and range iterable constant values, pre-building those constants ahead of time. This brings optimization support for Python3 ranges to what was available for Python2 already.

  • Avoid having a special node variange for range with no arguments, but create the exception raising node directly.

  • Specialized constant value nodes are using less generic implementations to query e.g. their length or iteration capabilities, which should speed up many checks on them.

  • Added support for the format built-in.

  • Python3: Added support for the ascii built-in.

Organizational

  • The movement to pure C got the final big push. All C++ only idoms of C++ were removed, and everything works with C11 compilers. A C++03 compiler can be used as a fallback, in case of MSVC or too old gcc for instance.
  • Using pure C, MinGW64 6x is now working properly. The latest version had problems with hypot related changes in the C++ standard library. Using C11 solves that.
  • This release also prepares Python 3.6 support, it includes full language support on the level of CPython 3.6.0b1.
  • The CPython 3.6 test suite was run with Python 3.5 to ensure bug level compatibility, and had a few findings of incompatibilities.

Cleanups

  • The last holdouts of classes in Nuitka were removed, and many idioms of C++ were stopped using.
  • Moved range related helper functions to a dedicated include file.
  • Using str is not bytes to detect Python3 str handling or actual bytes type existence.
  • Trace collections were using a mix-in that was merged with the base class that every user of it was having.

Tests

  • Added more static optimization tests, a lot more has become feasible to decide at run time, and is now done. These are to detect regressions in that domain.
  • The CPython 3.6 test suite is now also run with CPython 3.5 which found some incompatibilities.

Summary

This release marks a huge step forward. We are having the structure for type inference now. This will expand in coming releases to cover more cases, and there are many low hanging fruits for optimization. Specialized codes for variable versions of certain known shapes seems feasible now.

Then there is also the move towards pure C. This will make the backend compilation lighter, but due to using C11, we will not suffer any loss of convinience compared to "C-ish". The plan is to use continue to use C++ for compilation for compilers not capable of supporting C11.

The amount of static analysis done in Nuitka is now going to quickly expand, with more and more constructs predicted to raise errors or simplified. This will be an ongoing activity, as many types of expressions need to be enhanced, and only one missing will not let it optimize as well.

Also, it seems about time to add dedicated code for specific types to be as fast as C code. This opens up vast possibilities for acceleration and will lead us to zero overhead C bindings eventually. But initially the drive is towards enhanced import analysis, to become able to know the precide module expected to be imported, and derive type information from this.

The coming work will attack to start whole program optimization, as well as enhanced local value shape analysis, as well specialized type code generation, which will make Nuitka improve speed.

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