OpenVADL/openvadl
Nov 2024 – Oct 2025
11 Months active
Languages Used
CC++JavaPythonShellTableGenVHDLXML
Technical Skills
Compiler developmentEmbedded systemsLow-level programmingArithmetic Logic Unit (ALU) ImplementationBenchmarkingBuild Systems
Johannes Zottele
PROFILE
Johannes Zottele
Johannes Zottele developed core features and infrastructure for the OpenVADL/openvadl repository, focusing on processor modeling, code generation, and simulation fidelity. He engineered dynamic slicing and control-flow graph lowering in the compiler IR, enabling safer handling of undefined behavior and more robust optimizations. Leveraging Java and Kotlin, Johannes enhanced the type system, implemented alias register slicing, and expanded support for AArch64 and RISC-V architectures. His work included integrating advanced AST manipulation, improving CI/CD pipelines, and refining test automation. The depth of his contributions is reflected in the breadth of features delivered, demonstrating strong command of low-level systems and compiler development.
Overall Statistics
Feature vs Bugs
71%Features
Repository Contributions
366Total
Bugs
66
Commits
366
Features
163
Lines of code
215,605
Activity Months11
Your Network
19 people
Work History
October 2025
2 Commits • 2 Features
Oct 1, 2025OpenVADL - 2025-10 Monthly Summary Key features delivered: - DynSliceNode introduced to enable dynamic slicing in loops and code generation, based on expressions for msb/lsb (commit 2991bd11c8c787a0b995b2883bd78cd8bb23f3df). This lays the foundation for future dynamic slicing capabilities in IR and generated code. - IssSelectLoweringPass implemented to lower IssSelectNode into control-flow graphs (CFGs), ensuring undefined behavior (e.g., division by zero) is handled safely by evaluating only the relevant branch; includes new IR nodes (IssMoveNode, IssTempExprNode) and integration into existing passes (commit 2691d99c3ca99184835ac02be4cd73964e0cadaf). Major bugs fixed: - Improved safety around undefined behavior in generated IR by lowering conditional selects to CFGs, reducing risk of runtime errors due to premature evaluation of branches. Overall impact and accomplishments: - Strengthened the code generation foundation for dynamic slicing and safer IR transformations, enabling future features and more predictable optimizations. - Improved robustness and maintainability through explicit node types and clear lowering passes, with traceable commits. Technologies/skills demonstrated: - Compiler IR design and transformation (DynSliceNode, IssSelectLoweringPass, CFG-based lowering) - Dynamic slicing concepts and loop analysis - Safe code generation practices and undefined-behavior handling - Incremental integration and strong commit traceability
2 Commits • 2 Features
Oct 1, 2025OpenVADL - 2025-10 Monthly Summary Key features delivered: - DynSliceNode introduced to enable dynamic slicing in loops and code generation, based on expressions for msb/lsb (commit 2991bd11c8c787a0b995b2883bd78cd8bb23f3df). This lays the foundation for future dynamic slicing capabilities in IR and generated code. - IssSelectLoweringPass implemented to lower IssSelectNode into control-flow graphs (CFGs), ensuring undefined behavior (e.g., division by zero) is handled safely by evaluating only the relevant branch; includes new IR nodes (IssMoveNode, IssTempExprNode) and integration into existing passes (commit 2691d99c3ca99184835ac02be4cd73964e0cadaf). Major bugs fixed: - Improved safety around undefined behavior in generated IR by lowering conditional selects to CFGs, reducing risk of runtime errors due to premature evaluation of branches. Overall impact and accomplishments: - Strengthened the code generation foundation for dynamic slicing and safer IR transformations, enabling future features and more predictable optimizations. - Improved robustness and maintainability through explicit node types and clear lowering passes, with traceable commits. Technologies/skills demonstrated: - Compiler IR design and transformation (DynSliceNode, IssSelectLoweringPass, CFG-based lowering) - Dynamic slicing concepts and loop analysis - Safe code generation practices and undefined-behavior handling - Incremental integration and strong commit traceability
October 2025
September 2025
2 Commits • 1 Features
Sep 1, 2025September 2025 monthly summary for OpenVADL/openvadl: Delivered significant enhancements to alias registers, featuring wildcard access and overwrite semantics. Frontend changes implemented to support wildcard argument handling and refined alias register slicing for safety. No standalone bug fixes documented this month; focus on feature delivery that improves flexibility, safety, and developer productivity.
September 2025
2 Commits • 1 Features
Sep 1, 2025September 2025 monthly summary for OpenVADL/openvadl: Delivered significant enhancements to alias registers, featuring wildcard access and overwrite semantics. Frontend changes implemented to support wildcard argument handling and refined alias register slicing for safety. No standalone bug fixes documented this month; focus on feature delivery that improves flexibility, safety, and developer productivity.
August 2025
2 Commits • 1 Features
Aug 1, 2025August 2025 monthly summary for OpenVADL/openvadl: Implemented alias slice support across the type system and VHDL lowering. This feature enables type-checking of alias slices on registers and their lowering to VIAM, expanding aliasing capabilities and improving correctness for slice-based register aliases. The work enhances robustness, reduces downstream debugging, and establishes groundwork for future slice-aware optimizations. Key outcomes include improved type safety, automated translation to VIAM, and a more maintainable codegen path.
2 Commits • 1 Features
Aug 1, 2025August 2025 monthly summary for OpenVADL/openvadl: Implemented alias slice support across the type system and VHDL lowering. This feature enables type-checking of alias slices on registers and their lowering to VIAM, expanding aliasing capabilities and improving correctness for slice-based register aliases. The work enhances robustness, reduces downstream debugging, and establishes groundwork for future slice-aware optimizations. Key outcomes include improved type safety, automated translation to VIAM, and a more maintainable codegen path.
August 2025
July 2025
2 Commits • 1 Features
Jul 1, 2025July 2025 monthly summary for OpenVADL/openvadl: Delivered key formatting enhancements and corrected codegen behavior, driving migration readiness and code reliability.
July 2025
2 Commits • 1 Features
Jul 1, 2025July 2025 monthly summary for OpenVADL/openvadl: Delivered key formatting enhancements and corrected codegen behavior, driving migration readiness and code reliability.
June 2025
17 Commits • 7 Features
Jun 1, 2025June 2025 monthly summary: Delivered targeted features and stability improvements across the core OpenVADL/Openvadl stack, with a strong emphasis on correctness, performance, and tooling quality. Key feature work includes integrating an undefined-when annotation for AArch64 (with decoder integration and test/annotation coverage), expanding AArch64 test coverage for ADDW/SUBW shift instructions and updating the VADL model to handle shifts with proper type casting, and enabling VIAM language enhancements for forall loops (do, tensor, fold) with corresponding AST, codegen, and normalization integration. On the codegen and optimization front, we implemented control-flow optimization and inlining for constant-condition branches, cleaned up unused TCG conditions, and advanced select-node optimization to reduce runtime overhead. We inlined division-by-status builtins (SDIVS/UDIVS) with improved division-by-zero/overflow handling and extended tests. Lowering CTZ/COB to TCG and expanding ISS normalization to support CZB/COB nodes, plus related ROR normalization fixes, strengthened backend robustness. Additionally, CPU state/dataflow analysis improvements and AutoAssembler testing support improved reliability of state handling and automation coverage. Finally, CI/benchmarking and build alignment improvements reduced maintenance burden and improved feedback cycles (old CI cleanup, benchmark/script alignments, and including primecount benchmarks).
17 Commits • 7 Features
Jun 1, 2025June 2025 monthly summary: Delivered targeted features and stability improvements across the core OpenVADL/Openvadl stack, with a strong emphasis on correctness, performance, and tooling quality. Key feature work includes integrating an undefined-when annotation for AArch64 (with decoder integration and test/annotation coverage), expanding AArch64 test coverage for ADDW/SUBW shift instructions and updating the VADL model to handle shifts with proper type casting, and enabling VIAM language enhancements for forall loops (do, tensor, fold) with corresponding AST, codegen, and normalization integration. On the codegen and optimization front, we implemented control-flow optimization and inlining for constant-condition branches, cleaned up unused TCG conditions, and advanced select-node optimization to reduce runtime overhead. We inlined division-by-status builtins (SDIVS/UDIVS) with improved division-by-zero/overflow handling and extended tests. Lowering CTZ/COB to TCG and expanding ISS normalization to support CZB/COB nodes, plus related ROR normalization fixes, strengthened backend robustness. Additionally, CPU state/dataflow analysis improvements and AutoAssembler testing support improved reliability of state handling and automation coverage. Finally, CI/benchmarking and build alignment improvements reduced maintenance burden and improved feedback cycles (old CI cleanup, benchmark/script alignments, and including primecount benchmarks).
June 2025
May 2025
105 Commits • 55 Features
May 1, 2025May 2025 focused on strengthening OpenVADL/openvadl’s processor modeling, memory region handling, symbol resolution, and ISA coverage, while stabilizing CI and test workflows. Key deliverables include frontend grammar and processor lifecycle refactor, memory region support with ISS integration, expanded symbol resolution and annotation tooling, and RV32 CSR generation/spec support in ISS, all aimed at increasing simulation fidelity, hardware ISA coverage, and development velocity.
May 2025
105 Commits • 55 Features
May 1, 2025May 2025 focused on strengthening OpenVADL/openvadl’s processor modeling, memory region handling, symbol resolution, and ISA coverage, while stabilizing CI and test workflows. Key deliverables include frontend grammar and processor lifecycle refactor, memory region support with ISS integration, expanded symbol resolution and annotation tooling, and RV32 CSR generation/spec support in ISS, all aimed at increasing simulation fidelity, hardware ISA coverage, and development velocity.
April 2025
83 Commits • 28 Features
Apr 1, 2025April 2025 (OpenVADL/openvadl) focused on stabilizing CI/CD, improving docs publishing, modernizing the build system, and advancing core architecture with the RegisterTensor migration across VIAM/MI A/ISS. The efforts delivered tangible business value through more reliable release processes, clearer versioning, and a stronger build/test foundation, while expanding developer onboarding and documentation.
83 Commits • 28 Features
Apr 1, 2025April 2025 (OpenVADL/openvadl) focused on stabilizing CI/CD, improving docs publishing, modernizing the build system, and advancing core architecture with the RegisterTensor migration across VIAM/MI A/ISS. The efforts delivered tangible business value through more reliable release processes, clearer versioning, and a stronger build/test foundation, while expanding developer onboarding and documentation.
April 2025
March 2025
61 Commits • 26 Features
Mar 1, 2025March 2025 OpenVADL/openvadl monthly summary focused on strengthening foundations, boosting developer velocity, and advancing cross‑platform readiness. Delivered a robust build and CI foundation, advanced language and tooling capabilities, and improved test stability and documentation hygiene to accelerate business value across development and deployment pipelines.
March 2025
61 Commits • 26 Features
Mar 1, 2025March 2025 OpenVADL/openvadl monthly summary focused on strengthening foundations, boosting developer velocity, and advancing cross‑platform readiness. Delivered a robust build and CI foundation, advanced language and tooling capabilities, and improved test stability and documentation hygiene to accelerate business value across development and deployment pipelines.
February 2025
65 Commits • 31 Features
Feb 1, 2025February 2025 (OpenVADL/openvadl) delivered targeted codegen cleanup, performance-oriented ISS optimizations, relocation and lowering stability improvements, RISCV spec integration, and native tooling enhancements. These changes collectively strengthen reliability, performance, and extensibility of the OpenVADL toolchain, enabling faster iteration, more robust validation, and broader target support.
65 Commits • 31 Features
Feb 1, 2025February 2025 (OpenVADL/openvadl) delivered targeted codegen cleanup, performance-oriented ISS optimizations, relocation and lowering stability improvements, RISCV spec integration, and native tooling enhancements. These changes collectively strengthen reliability, performance, and extensibility of the OpenVADL toolchain, enabling faster iteration, more robust validation, and broader target support.
February 2025
January 2025
26 Commits • 11 Features
Jan 1, 2025January 2025 monthly summary for OpenVADL/openvadl: Delivered substantive ISS/TCG improvements, debugging enhancements, and CI/benchmark stabilization, with strengthened 64-bit RISC-V support. Key features include ISS: Translation and TCG optimization enabling multi-destination TCGv, added SDIV/UDIV/SelectNode/SREM/UREM support, improved jump-slot assignment, and long multiplication decomposition for 64-bit architectures; refactored TCG Context and variable assignment; removal of unused code paths. VIAM: fixed ExpressionNode copy() to consistently return an ExpressionNode. PASS/EMBench/CI: enhanced exception dumps for debugging; timing adjustments for embench and spike board set to 10 MHz; embench now runs on rv64im for accuracy. CLI/CI/QC: fixed a CLI typo, set GraalVM JDK in misc.xml, suppressed a Checkstyle warning, added RV64 M extension tests, ISS test gating via environment variable, fixed the first ISS test and InstrInfoTableGen snapshot; added documentation and DefinitionExtension metadata; ran embench on rv64im for validation.
January 2025
26 Commits • 11 Features
Jan 1, 2025January 2025 monthly summary for OpenVADL/openvadl: Delivered substantive ISS/TCG improvements, debugging enhancements, and CI/benchmark stabilization, with strengthened 64-bit RISC-V support. Key features include ISS: Translation and TCG optimization enabling multi-destination TCGv, added SDIV/UDIV/SelectNode/SREM/UREM support, improved jump-slot assignment, and long multiplication decomposition for 64-bit architectures; refactored TCG Context and variable assignment; removal of unused code paths. VIAM: fixed ExpressionNode copy() to consistently return an ExpressionNode. PASS/EMBench/CI: enhanced exception dumps for debugging; timing adjustments for embench and spike board set to 10 MHz; embench now runs on rv64im for accuracy. CLI/CI/QC: fixed a CLI typo, set GraalVM JDK in misc.xml, suppressed a Checkstyle warning, added RV64 M extension tests, ISS test gating via environment variable, fixed the first ISS test and InstrInfoTableGen snapshot; added documentation and DefinitionExtension metadata; ran embench on rv64im for validation.
November 2024
1 Commits
Nov 1, 2024November 2024 (OpenVADL/openvadl): Generalized truncation generation across all bit widths, replacing a conditional-specific approach with a single, uniform implementation. This fixes the truncation generation for 32-bit integers and improves correctness, consistency, and maintainability across 8/16/32-bit truncations. The change reduces edge-case risk and aligns behavior with the project's design goals. Impact includes improved reliability in downstream components, easier future enhancements, and cleaner integration with the truncation framework.
1 Commits
Nov 1, 2024November 2024 (OpenVADL/openvadl): Generalized truncation generation across all bit widths, replacing a conditional-specific approach with a single, uniform implementation. This fixes the truncation generation for 32-bit integers and improves correctness, consistency, and maintainability across 8/16/32-bit truncations. The change reduces edge-case risk and aligns behavior with the project's design goals. Impact includes improved reliability in downstream components, easier future enhancements, and cleaner integration with the truncation framework.
November 2024
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Quality Metrics
Correctness88.8%
Maintainability86.8%
Architecture85.4%
Performance79.6%
AI Usage20.4%
Skills & Technologies
Programming Languages
ANTLRAssemblyBashCC++CSSDockerfileDoxygenGitGradle
Technical Skills
AArch64 ArchitectureAPI DesignARM ArchitectureAST ManipulationAST manipulationAbstract Syntax Tree (AST)Abstract Syntax Tree (AST) ManipulationAbstract Syntax TreesAbstract Syntax Trees (AST)Annotation ProcessingArchitecture DefinitionArchitecture Definition LanguageArchive ExtractionArithmetic Logic Unit (ALU) ImplementationArithmetic Operations
Repositories Contributed To
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