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1	Index

Open Catalog of Code Guidelines for Correctness, Modernization, and Optimization

About

This Open Catalog is a collaborative effort to consolidate expert knowledge on code guidelines for the correctness, modernization, and optimization of code written in C, C++, and Fortran programming languages. The Catalog consists of a comprehensive set of checks (rules) that describe specific issues in the source code and provide guidance on corrective actions, along with extensive documentation, example codes and references to additional reading resources.

Benchmarks

The Open Catalog includes a suite of microbenchmarks designed to demonstrate:

• No performance degradation when implementing the correctness and modernization recommendations.
• Potential performance enhancements achievable through the optimization recommendations.

Checks

ID	Title	C	Fortran	C++	AutoFix
PWR001	Declare global variables as function parameters	✓	✓	✓
PWR002	Declare scalar variables in the smallest possible scope	✓		✓
PWR003	Explicitly declare pure functions	✓	✓	✓
PWR004	Declare OpenMP scoping for all variables	✓	✓	✓
PWR005	Disable default OpenMP scoping	✓	✓	✓
PWR006	Avoid privatization of read-only variables	✓	✓	✓
PWR007	Disable implicit declaration of variables		✓		✓1
PWR008	Declare the intent for each procedure parameter		✓		✓1
PWR009	Use OpenMP teams to offload work to GPU	✓	✓	✓
PWR010	Avoid column-major array access in C/C++	✓		✓
PWR012	Pass only required fields from derived type as parameters	✓	✓	✓
PWR013	Avoid copying unused variables to or from the GPU	✓	✓	✓
PWR014	Out-of-dimension-bounds matrix access	✓		✓
PWR015	Avoid copying unnecessary array elements to or from the GPU	✓	✓	✓
PWR016	Use separate arrays instead of an Array-of-Structs	✓	✓	✓
PWR017	Using countable while loops instead of for loops may inhibit vectorization	✓		✓
PWR018	Call to recursive function within a loop inhibits vectorization	✓	✓	✓
PWR019	Consider interchanging loops to favor vectorization by maximizing inner loop's trip count	✓	✓	✓
PWR020	Consider loop fission to enable vectorization	✓	✓	✓
PWR021	Consider loop fission with scalar to vector promotion to enable vectorization	✓	✓	✓
PWR022	Move invariant conditional out of the loop to facilitate vectorization	✓	✓	✓
PWR023	Add 'restrict' for pointer function parameters to hint the compiler that vectorization is safe	✓		✓
PWR024	Loop can be rewritten in OpenMP canonical form	✓		✓
PWR025	Consider annotating pure function with OpenMP 'declare simd'	✓	✓	✓
PWR026	Annotate function for OpenMP Offload	✓	✓	✓
PWR027	Annotate function for OpenACC Offload	✓	✓	✓
PWR028	Remove pointer increment preventing performance optimization	✓		✓
PWR029	Remove integer increment preventing performance optimization	✓	✓	✓
PWR030	Remove pointer assignment preventing performance optimization for perfectly nested loops	✓	✓	✓
PWR031	Replace pow by multiplication, division and/or square root	✓	✓	✓
PWR032	Avoid calls to mathematical functions with higher precision than required	✓		✓
PWR033	Move invariant conditional out of the loop to avoid redundant computations	✓	✓	✓
PWR034	Avoid strided array access to improve performance	✓	✓	✓
PWR035	Avoid non-consecutive array access to improve performance	✓	✓	✓
PWR036	Avoid indirect array access to improve performance	✓	✓	✓
PWR037	Potential precision loss in call to mathematical function	✓		✓
PWR039	Consider loop interchange to improve the locality of reference and enable vectorization	✓	✓	✓	✓1
PWR040	Consider loop tiling to improve the locality of reference	✓	✓	✓
PWR042	Consider loop interchange by promoting the scalar reduction variable to an array	✓	✓	✓
PWR043	Consider loop interchange by replacing the scalar reduction value	✓	✓	✓
PWR044	Avoid unnecessary floating-point data conversions involving constants	✓		✓
PWR045	Replace division with a multiplication with a reciprocal	✓		✓
PWR046	Replace two divisions with a division and a multiplication	✓	✓	✓
PWR048	Replace multiplication/addition combo with an explicit call to fused multiply-add	✓		✓
PWR049	Move iterator-dependent condition outside of the loop	✓	✓	✓
PWR050	Consider applying multithreading parallelism to forall loop	✓	✓	✓	✓1
PWR051	Consider applying multithreading parallelism to scalar reduction loop	✓	✓	✓	✓1
PWR052	Consider applying multithreading parallelism to sparse reduction loop	✓	✓	✓	✓1
PWR053	Consider applying vectorization to forall loop	✓	✓	✓	✓1
PWR054	Consider applying vectorization to scalar reduction loop	✓	✓	✓	✓1
PWR055	Consider applying offloading parallelism to forall loop	✓	✓	✓	✓1
PWR056	Consider applying offloading parallelism to scalar reduction loop	✓	✓	✓	✓1
PWR057	Consider applying offloading parallelism to sparse reduction loop	✓	✓	✓	✓1
PWR060	Consider loop fission to separate gather memory access pattern	✓	✓	✓
PWR062	Consider loop interchange by removing accumulation on array value	✓	✓	✓
PWR063	Avoid using legacy Fortran constructs		✓
PWR068	Encapsulate procedures within modules to avoid the risks of calling implicit interfaces		✓
PWR069	Use the keyword only to explicitly state what to import from a module		✓		✓1
PWR070	Declare array dummy arguments as assumed-shape arrays		✓
PWR071	Prefer real(kind=kind_value) for declaring consistent floating types		✓
PWR072	Split the variable initialization from the declaration to prevent the implicit 'save' behavior		✓		✓1
PWR073	Transform common block into a module for better data encapsulation		✓
PWR075	Avoid using GNU Fortran extensions		✓
PWR079	Avoid undefined behavior due to uninitialized variables	✓	✓	✓
PWD002	Unprotected multithreading reduction operation	✓	✓	✓
PWD003	Missing array range in data copy to the GPU	✓	✓	✓
PWD004	Out-of-memory-bounds array access	✓	✓	✓
PWD005	Array range copied to or from the GPU does not cover the used range	✓	✓	✓
PWD006	Missing deep copy of non-contiguous data to the GPU	✓	✓	✓
PWD007	Unprotected multithreading recurrence	✓	✓	✓
PWD008	Unprotected multithreading recurrence due to out-of-dimension-bounds array access	✓	✓	✓
PWD009	Incorrect privatization in parallel region	✓	✓	✓
PWD010	Incorrect sharing in parallel region	✓	✓	✓
PWD011	Missing OpenMP lastprivate clause	✓	✓	✓
RMK001	Loop nesting that might benefit from hybrid parallelization using multithreading and SIMD	✓	✓	✓
RMK002	Loop nesting that might benefit from hybrid parallelization using offloading and SIMD	✓	✓	✓
RMK003	Potentially privatizable temporary variable	✓		✓
RMK007	SIMD opportunity within a multithreaded region	✓	✓	✓
RMK008	SIMD opportunity within an offloaded region	✓	✓	✓
RMK009	Outline loop to increase compiler and tooling code coverage	✓		✓
RMK010	The vectorization cost model states the loop is not a SIMD opportunity due to strided memory accesses in the loop body	✓	✓	✓
RMK012	The vectorization cost model states the loop is not a SIMD opportunity because conditional execution renders vectorization inefficient	✓	✓	✓
RMK013	The vectorization cost model states the loop is not a SIMD opportunity because loops with low trip count unknown at compile time do not benefit from vectorization	✓	✓	✓
RMK014	The vectorization cost model states the loop is not a SIMD opportunity due to unpredictable memory accesses in the loop body	✓	✓	✓
RMK015	Tune compiler optimization flags to increase the speed of the code	✓	✓	✓
RMK016	Tune compiler optimization flags to avoid potential changes in floating point precision	✓	✓	✓

AutoFix: Denotes tools that support automatic correction of the corresponding check. Readers are encouraged to report additional tools with autofix capabilities for these checks. The tools are tagged in the table as follows:

Contributing

We welcome and encourage contributions to the Open Catalog! Here's how you can get involved:

1. Join the discussion:

   Got ideas, questions, or suggestions? Head over to our GitHub Discussions. It's the perfect place for open-ended conversations and brainstorming!

2. Report issues:

   Found inaccuracies, unclear explanations, or other problems? Please open an Issue. Detailed reports help us quickly improve the quality of the project!

3. Submit pull requests:

   Interested in solving any issues? Feel free to fork the repository, make your changes, and submit a Pull Request. We'd love to see your contributions!

Footnotes

1. Codee ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³