hohn/codeql
1
0
Fork 0
mirror of https://github.com/github/codeql.git synced 2026-05-02 12:15:17 +02:00
Code Issues Packages Projects Releases Wiki Activity

Tidy up some references

Browse Source
This commit is contained in:
Felicity Chapman
2020-02-18 16:05:01 +00:00
parent 8a44f51fc5
commit 74d93ba704
6 changed files with 17 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
docs/language/learn-ql/python/control-flow.rst
View File

@@ -3,7 +3,7 @@ Analyzing control flow in Python
You can write CodeQL queries to explore the control flow graph of a Python program, for example, to discover unreachable code or mutually exclusive blocks of code.
To analyze the `Control-flow graph <http://en.wikipedia.org/wiki/Control_flow_graph>`__ of a ``Scope`` we can use the two CodeQL classes ``ControlFlowNode`` and ``BasicBlock``. These classes allow you to ask such questions as "can you reach point A from point B?" or "Is it possible to reach point B *without* going through point A?". To report results we use the class ``AstNode``, which represents a syntactic element and corresponds to the source code - allowing the results of the query to be more easily understood.
To analyze the control-flow graph of a ``Scope`` we can use the two CodeQL classes ``ControlFlowNode`` and ``BasicBlock``. These classes allow you to ask such questions as "can you reach point A from point B?" or "Is it possible to reach point B *without* going through point A?". To report results we use the class ``AstNode``, which represents a syntactic element and corresponds to the source code - allowing the results of the query to be more easily understood. For more information, see `Control-flow graph <http://en.wikipedia.org/wiki/Control_flow_graph>`__ in Wikipedia.
The ``ControlFlowNode`` class
-----------------------------
@@ -55,12 +55,12 @@ Example finding unreachable statements
where not exists(s.getAFlowNode())
select s
➤ `See this in the query console <https://lgtm.com/query/670720181/>`__. This query gives fewer results, but most of the projects have some unreachable nodes. These are also highlighted by the standard query: `Unreachable code <https://lgtm.com/rules/3980095>`__.
➤ `See this in the query console <https://lgtm.com/query/670720181/>`__. This query gives fewer results, but most of the projects have some unreachable nodes. These are also highlighted by the standard query: unreachable code. For more information, see `Unreachable code <https://lgtm.com/rules/3980095>`__ on LGTM.com.
The ``BasicBlock`` class
------------------------
The ``BasicBlock`` class represents a `basic block <http://en.wikipedia.org/wiki/Basic_block>`__ of control flow nodes. The ``BasicBlock`` class is not that useful for writing queries directly, but is very useful for building complex analyses, such as data flow. The reason it is useful is that it shares many of the interesting properties of control flow nodes, such as what can reach what and what `dominates <http://en.wikipedia.org/wiki/Dominator_%28graph_theory%29>`__ what, but there are fewer basic blocks than control flow nodes - resulting in queries that are faster and use less memory.
The ``BasicBlock`` class represents a basic block of control flow nodes. The ``BasicBlock`` class is not that useful for writing queries directly, but is very useful for building complex analyses, such as data flow. The reason it is useful is that it shares many of the interesting properties of control flow nodes, such as, what can reach what, and what dominates what, but there are fewer basic blocks than control flow nodes - resulting in queries that are faster and use less memory. For more information, see `basic block <http://en.wikipedia.org/wiki/Basic_block>`__ and `dominates <http://en.wikipedia.org/wiki/Dominator_%28graph_theory%29>`__ on Wikipedia.
Example finding mutually exclusive basic blocks
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^