John Mccall
Software Engineer at Apple
San Francisco, California, United States
Summary
🤩
Rockstar🎓
Top SchoolJohn Mccall is a seasoned software engineer and language designer with 19 years of experience, currently leading core Swift and Objective-C language design and implementation at Apple in San Francisco. He has driven ABI and runtime design, implemented major features like Swift error handling and Objective-C ARC, and serves as a code owner for LLVM IR generation in Clang. His deep systems work spans compiler backends, SIL transformations, and GPU codegen (NVPTX), reflecting rare expertise across language design, compiler internals, and low-level code generation. A Carnegie Mellon–trained mathematician/computer scientist with an MS from Portland State, he also provides technical leadership to ~20 engineers while continuing hands-on contributions to high-profile open-source projects such as Swift and Clang. An under-the-radar detail: he architected substantial parts of the value-ownership model and runtime optimizations that quietly improve performance and safety across Apple’s platforms.
20 years of coding experience
3 years of employment as a software developer
M.S., Computer Science, M.S., Computer Science at Portland State UniversityB.S., Mathematics, Computer Science, B.S., Mathematics, Computer Science at Carnegie Mellon University
Github Skills (32)
objective-c10
c-language10
runtimes10
system-programming10
foundation10
llvm10
compiler-development10
gpu-programming10
run-time10
foundation-sites10
nvtx10
code-generation10
sys10
intermediate-language10
ptx10
Programming languages (14)
Github contributions (5)
llvm-mirror/clang
Jul 2009 - Oct 2019
Mirror kept for legacy. Moved to https://github.com/llvm/llvm-project
Role in this project:
Back-end Developer
Back-end DeveloperContributions:1730 commits in 10 years 4 months
Contributions summary:John made significant contributions to the clang compiler project, primarily focusing on code generation related to Objective-C and C++ features. Their work involved implementing new features, such as handling the swiftcall calling convention and support for Microsoft's __declspec(property) attribute, and addressing bugs in the handling of Objective-C property declarations and lambda-to-block conversions, including correcting memory management issues. They also made substantial improvements to the IRGen code related to atomics and vector types, making code more efficient and consistent.
llvmcompilerc-plus-pluscobjective-c
apple/swift-clang
Nov 2015 - Oct 2018
Role in this project:Back-end Developer
Back-end DeveloperContributions:75 commits, 9 PRs, 29 pushes in 3 years
Contributions summary:John made significant contributions to the `apple/swift-clang` repository, focusing on implementing ARC-related optimizations and features within the compiler. They added calls to `objc_unsafeClaimAutoreleasedReturnValue` to manage memory and reduce overhead. They also introduced an ARC autoreleased-return-value caller marker on i386 and i386 targets, indicating work related to compiler optimization and potentially performance enhancement. Additionally, the user contributed to improvements in the API Notes management.
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