[pypy-svn] r38920 - pypy/dist/pypy/doc/config

[mwh at codespeak.net]

Author: mwh
Date: Thu Feb 15 17:44:01 2007
New Revision: 38920

Modified:
   pypy/dist/pypy/doc/config/translation.backendopt.mallocs.txt
Log:
document translation.backendopt.mallocs


Modified: pypy/dist/pypy/doc/config/translation.backendopt.mallocs.txt
==============================================================================
--- pypy/dist/pypy/doc/config/translation.backendopt.mallocs.txt	(original)
+++ pypy/dist/pypy/doc/config/translation.backendopt.mallocs.txt	Thu Feb 15 17:44:01 2007
@@ -0,0 +1,29 @@
+This optimization enables "malloc removal", which "explodes"
+allocations of structures which do not escape from the function they
+are allocated in into one or more additional local variables.
+
+An example.  Consider this rather unlikely seeming code::
+
+    class C:
+        pass
+    def f(y):
+        c = C()
+        c.x = y
+        return c.x
+
+Malloc removal will spot that the ``C`` object can never leave ``f``
+and replace the above with code like this::
+
+    def f(y):
+        _c__x = y
+        return _c__x
+
+It is rare for code to be directly written in a way that allows this
+optimization to be useful, but inlining often results in opportunities
+for its use (and indeed, this is one of the main reasons PyPy does its
+own inlining rather than relying on the C compilers).
+
+For much more information about this and other optimizations you can
+read section 4.1 of the `technical report on "Massive Parallelism and
+Translation Aspects"
+<http://codespeak.net/pypy/extradoc/eu-report/D07.1_Massive_Parallelism_and_Translation_Aspects-2006-12-15.pdf>`__.