Ulrich Weigand
Distinguished Engineer at IBM Deutschland Research & Development GmbH
Stuttgart Region Germany
Summary
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RockstarUlrich Weigand is a Distinguished Engineer with 24 years of hands-on experience building and hardening low-level systems and runtimes from Stuttgart, Germany. He has deep expertise in cross-platform compatibility, endianness, and ABI/calling-convention work across major open-source projects including LLVM/Clang, lldb, .NET runtime, ASP.NET Core and the Wasmtime WebAssembly runtime. At IBM he progressed from senior engineer to Distinguished Engineer, driving platform-level fixes and architecture-specific support (notably SystemZ and s390x) that enable debugging, JIT, and runtime correctness on uncommon big-endian systems. His contributions show a rare blend of compiler backend, runtime, and networking internals knowledge—down to string, GUID, and IP handling at the byte-order level. Colleagues rely on him to solve subtle portability and performance regressions that surface only on niche architectures.
24 years of coding experience
8 years of employment as a software developer
Github Skills (52)
arcgisruntime10
kestrel10
debugging10
debug10
c-language10
assembly10
runtimes10
endianness10
s390x10
computer-architecture10
architecture10
llvm10
testing10
atomics10
net10
Programming languages (13)
Github contributions (5)
bytecodealliance/wasmtime
Nov 2020 - Jan 2023
A lightweight WebAssembly runtime that is fast, secure, and standards-compliant
Role in this project:
Back-end Developer
Back-end DeveloperContributions:84 reviews, 87 commits, 92 PRs in 2 years 2 months
Contributions summary:Ulrich made significant contributions to the wasmtime project, focusing on low-level aspects of WebAssembly runtime implementation. Their work involved deep dives into the ABI (Application Binary Interface) for different architectures, including S390x, AArch64, and x64, specifically addressing stack alignment and argument handling. The user also contributed to code generation and the linker, implementing support for features like the stack backchain and fixes for endianness issues in the JIT (Just-In-Time) build process. They also added support for atomic operations and various features for the s390x architecture, enabling a more complete backend.
securejitcraneliftrustruntime
llvm/llvm-project
Nov 2019 - Apr 2025
The LLVM Project is a collection of modular and reusable compiler and toolchain technologies.
Role in this project:Back-end Developer
Back-end DeveloperContributions:289 reviews, 52 PRs, 140 pushes in 5 years 5 months
Contributions summary:Ulrich primarily contributed to the LLVM project by addressing issues related to the Clang compiler and SystemZ backend. Their work involved fixing code generation for _[u]128 intrinsics, implementing i128 funnel shifts, and optimizing vector zero/sign extensions, demonstrating proficiency in low-level code optimization. The user also added support for the arch15 CPU architecture, showcasing their knowledge of processor-specific instruction sets and assembler/disassembler functionality. Furthermore, they worked on fixing calling conventions and address parsing issues related to the SystemZ architecture.
compilerstechnologiesclangsubmittoolchain
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