DeadCode: Eliminate out-of-scope results, handle templates and multiple compilation
#717
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Eliminate false positives where a line of code is used in some copies (instances) but not others.
Add a utility library for determing whether a condition holds for all copies of a statement in a program.
The modifications to the query to handle multiple copies of a statement across different targets also support reporting of issues across multiple template instantiations. This commit adds additional tests to demonstrate that this works effectively.
Ensure that macro expansions and multiple instances of code work together.
The rule description for this rule in fact talks about dead operations, not dead statements. Therefore: - Unshare the rule from MISRA C++ 2008 - Implement dead operation, as per the rule
Use the HoldsForAllInstances module to eliminate cases where a line of code is compiled into multiple targets with different dead code behaviour.
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Sep 26, 2024
MichaelRFairhurst
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Sep 26, 2024
| * A module for considering whether a result occurs in all instances (e.g. copies) of the code at a | ||
| * given location. | ||
| */ | ||
| module HoldsForAllInstances<CandidateStmtSig CandidateStmt> { |
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Minor, would it be better to name this HoldsForAllCopies?
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| } | ||
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| /** A candidate set of types. */ |
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This comment could be elaborated, for instance, A statement type T that satisfies a relevant predicate, such that ``HoldsForAllInstances<T>::LogicalResultStmt`` points to _all_ copies of that statement iff all copies of that statement satisfy the relevant predicate as well.
Oof, tricky to word the docs on this one! 😄
| } | ||
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| /** | ||
| * A logical result statement, representing all instances of a statement that occur at the same |
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Or something like, "The set of all statements that satisfy the predicate type CandidateStmtSig, iff all copies of that statement also satisfy the relevant predicate."
cpp/common/src/codingstandards/cpp/alertreporting/HoldsForAllInstances.qll
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Description
Fixes #716, #715 and #604:
RULE-2-2is modified to match the rule text, now only reporting "operations" not statements.M0-1-9andRULE-2-2now handle cases where a line of code is compiled multiple times (e.g. templates, different targets), and has differing dead code states in each. We now only report a line of code as dead if it is dead in all instances.RULE-2-2provides a better alert message.Change request type
.ql,.qll,.qlsor unit tests)Rules with added or modified queries
M0-1-9RULE-2-2Release change checklist
A change note (development_handbook.md#change-notes) is required for any pull request which modifies:
If you are only adding new rule queries, a change note is not required.
Author: Is a change note required?
🚨🚨🚨
Reviewer: Confirm that format of shared queries (not the .qll file, the
.ql file that imports it) is valid by running them within VS Code.
Reviewer: Confirm that either a change note is not required or the change note is required and has been added.
Query development review checklist
For PRs that add new queries or modify existing queries, the following checklist should be completed by both the author and reviewer:
Author
As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.
Reviewer
As a rule of thumb, predicates specific to the query should take no more than 1 minute, and for simple queries be under 10 seconds. If this is not the case, this should be highlighted and agreed in the code review process.