codeql/change-notes/1.22/analysis-cpp.md

Improvements to C/C++ analysis

General improvements

New queries

Query	Tags	Purpose

Changes to existing queries

Query	Expected impact	Change
Call to alloca in a loop (cpp/alloca-in-loop)	Fewer false positive results	Fixed false positives where the stack allocation could not be reached multiple times in the loop, typically due to a break or return statement.
Continue statement that does not continue (cpp/continue-in-false-loop)	Fewer false positive results	Analysis is now restricted to do-while loops. This query is now run and displayed by default on LGTM.
Expression has no effect (cpp/useless-expression)	Fewer false positive results	Calls to functions with the weak attribute are no longer considered to be side effect free, because they could be overridden with a different implementation at link time.
No space for zero terminator (cpp/no-space-for-terminator)	Fewer false positive results	False positives involving strings that are not null-terminated have been excluded.
Sign check of bitwise operation (cpp/bitwise-sign-check)	Fewer false positive results and more true positive results	The query now understands the direction of each comparison, making it more accurate.
Suspicious pointer scaling (cpp/suspicious-pointer-scaling)	Lower precision	The precision of this query has been reduced to "medium". This coding pattern is used intentionally and safely in a number of real-world projects. Results are no longer displayed on LGTM unless you choose to display them.
Non-constant format string (cpp/non-constant-format)	Fewer false positive results	Rewritten using the taint-tracking library.
Variable used in its own initializer (cpp/use-in-own-initializer)	Fewer false positive results	False positives for constant variables with the same name in different namespaces have been removed.

Changes to QL libraries

• The predicate Variable.getAnAssignedValue() now reports assignments to fields resulting from aggregate initialization ( = {...}).
• The predicate TypeMention.toString() has been simplified to always return the string "type mention". This may improve performance when using Element.toString() or its descendants.
• The semmle.code.cpp.security.TaintTracking library now considers a pointer difference calculation as blocking taint flow.
• Fixed the LocalScopeVariableReachability.qll library's handling of loops with an entry condition is both always true upon first entry, and where there is more than one control flow path through the loop condition. This change increases the accuracy of the LocalScopeVariableReachability.qll library and queries which depend on it.
• The semmle.code.cpp.models library now models data flow through std::swap.