19 March 2015

Nuitka Release 0.5.11

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

The last release represented a significant change and introduced a few regressions, which got addressed with hot fix releases. But it also had a focus on cleaning up open optimization issues that were postponed in the last release.

New Features

The filenames of source files as found in the __file__ attribute are now made relative for all modes, not just standalone mode.

This makes it possible to put data files along side compiled modules in a deployment.

Bug Fixes

Local functions that reference themselves were not released. They now are.
```
def someFunction():
    def f():
        f()  # referencing 'f' in 'f' caused the garbage collection to fail.
```
Recent changes to code generation attached closure variable values to the function object, so now they can be properly visited. Fixed in 0.5.10.1 already.
Python2.6: The complex constants with real or imaginary parts -0.0 were collapsed with constants of value 0.0. This became more evident after we started to optimize the complex built-in. Fixed in 0.5.10.1 already.
```
complex(0.0, 0.0)
complex(-0.0, -0.0)  # Could be confused with the above.
```
Complex call helpers could leak references to their arguments. This was a regression. Fixed in 0.5.10.1 already.
Parameter variables offered as closure variables were not properly released, only the cell object was, but not the value. This was a regression. Fixed in 0.5.10.1 already.
Compatibility: The exception type given when accessing local variable values not initialized in a closure taking function, needs to be NameError and UnboundLocalError for accesses in the providing function. Fixed in 0.5.10.1 already.
Fix support for “venv” on systems, where the system Python uses symbolic links too. This is the case on at least on Mageia Linux. Fixed in 0.5.10.2 already.
Python3.4: On systems where long and Py_ssize_t are different (e.g. Win64) iterators could be corrupted if used by uncompiled Python code. Fixed in 0.5.10.2 already.
Fix, generator objects didn’t release weak references to them properly. Fixed in 0.5.10.2 already.
Compatibility: The __closure__ attributes of functions was so far not supported, and rarely missing. Recent changes made it easy to expose, so now it was added.
macOS: A linker warning about deprecated linker option -s was solved by removing the option.
Compatibility: Nuitka was enforcing that the __doc__ attribute to be a string object, and gave a misleading error message. This check must not be done though, __doc__ can be any type in Python.

Optimization

Variables that need not be shared, because the uses in closure taking functions were eliminated, no longer use cell objects.
The try/except and try/finally statements now both have actual merging for SSA, allowing for better optimization of code behind it.
```
def f():

    try:
        a = something()
    except:
        return 2

    # Since the above exception handling cannot continue the code flow,
    # we do not have to invalidate the trace of "a", and e.g. do not have
    # to generate code to check if it's assigned.
    return a
```
Since try/finally is used in almost all re-formulations of complex Python constructs this is improving SSA application widely. The uses of try/except in user code will no longer degrade optimization and code generation efficiency as much as they did.
The try/except statement now reduces the scope of tried block if possible. When no statement raised, already the handling was removed, but leading and trailing statements that cannot raise, were not considered.
```
def f():

    try:
        b = 1
        a = something()
        c = 1
    except:
        return 2
```
This is now optimized to.
```
def f():

    b = 1
    try:
        a = something()
    except:
        return 2
    c = 1
```
The impact may on execution speed may be marginal, but it is definitely going to improve the branch merging to be added later. Note that c can only be optimized, because the exception handler is aborting, otherwise it would change behaviour.
The creation of code objects for standalone mode and now all code objects was creating a distinct filename object for every function in a module, despite them being same content. This was wasteful for module loading. Now it’s done only once.

Also, when having multiple modules, the code to build the run time filename used for code objects, was calling import logic, and doing lookups to find os.path.join again and again. These are now cached, speeding up the use of many modules as well.

Cleanups

Nuitka used to have “variable usage profiles” and still used them to decide if a global variable is written to, in which case, it stays away from doing optimization of it to built-in lookups, and later calls.

The have been replaced by “global variable traces”, which collect the traces to a variable across all modules and functions. While this is now only a replacement, and getting rid of old code, and basing on SSA, later it will also allow to become more correct and more optimized.
The standalone now queries its hidden dependencies from a plugin framework, which will become an interface to Nuitka internals in the future.

Testing

The use of deep hashing of constants allows us to check if constants become mutated during the run-time of a program. This allows to discover corruption should we encounter it.
The tests of CPython are now also run with Python in debug mode, but only on Linux, enhancing reference leak coverage.
The CPython test parts which had been disabled due to reference cycles involving compiled functions, or usage of __closure__ attribute, were reactivated.

Organizational

Since Google Code has shutdown, it has been removed from the Nuitka git mirrors.

Summary

This release brings exciting new optimization with the focus on the try constructs, now being done more optimal. It is also a maintenance release, bringing out compatibility improvements, and important bug fixes, and important usability features for the deployment of modules and packages, that further expand the use cases of Nuitka.

The git flow had to be applied this time to get out fixes for regression bug fixes, that the big change of the last release brought, so this is also to consolidate these and the other corrections into a full release before making more invasive changes.

The cleanups are leading the way to expanded SSA applied to global variable and shared variable values as well. Already the built-in detect is now based on global SSA information, which was an important step ahead.

Nuitka Release 0.5.10 Nuitka Release 0.5.12