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The Shift of Theseus — Toy Bit Provenance Abstract Domain
CF Bolz-Tereick extends PyPy's Toy Optimizer with a bit provenance abstract domain that tracks where each bit of a value came from, letting the JIT recognize shifts, masks and identities across instruction sequences that a known-bits domain misses, with transfer functions, rewrite extraction and an evaluation on Pydrofoil and PyPy.
25 min · 5,858 words
Precedence levels are dead; long live precedence sets
Prompted by Zig's new partial-order operator precedence, this post explains how parsers can replace numeric precedence levels with precedence sets, showing that a level-based Pratt-style parser can be converted to a set-based one using a few bitwise tricks such as isolating and clearing the lowest set bit.
3 min · 691 words
writing about pratt parsing so I remember it
A hands-on walkthrough of Pratt parsing for C expressions: why it rarely shows up in standard compiler courses, how binding power handles precedence and associativity, and how prefix, infix and postfix subroutines keep the parser core small, with pointers to Crafting Interpreters.
5 min · 1,260 words
Max Slater introduces Syl, a systems language that encodes compile-time computation in a modal type system inspired by two-level type theory and OxCaml: values carry staticity and erasure modes, enabling dependent types, proofs and totality checks, with examples like a typed interpreter and length-indexed vectors and planned extensions such as modules, reflection and user-defined layouts.
11 min · 2,608 words
The glorious @xkcdRandom Zig builtin
Adolfo Ochagavía forks the Zig compiler to add a tongue-in-cheek @xkcdRandom builtin that always returns 4, using the joke as a hands-on tour of how Zig builtins are declared, analyzed, and lowered inside the compiler.
3 min · 605 words
Attention people who think UB is fine
Thomas Habets follows up his post on undefined behaviour in C with a concrete example showing that UB is not 'at worst a segfault': the same line can run whatever is next in memory, write a random value and crash, or do what you naively expect.
3 min · 609 words
How close can pure FP get to C?
Richard Feldman takes up the lean-zip versus libdeflate result and explores how far a DEFLATE implementation in Roc, a pure functional language, can be pushed toward C performance, with benchmarks, compiler work, and reproduction scripts.
41 min · 9,413 words
Objects, attributes, maps, oh my!
Max Bernstein walks through how dynamic language VMs move from hash-table objects to hidden classes (shapes or maps) and inline caches, with Python sketches and notes on how ZJIT handles polymorphic shapes in Ruby.
13 min · 3,019 words
Using a lookup-table to correct an approximation
A corsix.org post on compiling enum-to-string functions compactly: instead of a switch or a full offset table, compute a fast but incorrect approximation of each string's offset and fix it with a small table of corrections, a general trick compilers still miss.
4 min · 827 words
Papers We Love: Flow Typing, A New Lens on Linearity
Jared Forsyth works through a new paper on flow typing that aims to make linear types far less cumbersome, implementing its execution model and explaining how it treats values as pass-by-value with immutable updates, and what that could mean for language design.
6 min · 1,388 words
Announcing the GPU notification group and Linker Working Area
The Rust compiler team announces a GPU-target notification group for vendor experts helping diagnose GPU backend issues, plus a Linker working area to integrate alternative linkers such as Wild and to field linker questions, with Zulip streams and signup via rust-lang/team.
1 min · 295 words
Borrow Checking Zero-Cost Cyclic Mutability
Jake Fecher describes the new design of Ante's borrow checker, which blends group borrowing with his own ideas to relax Rust's aliasing-xor-mutation rule while still statically preventing dangling pointers, enabling safe shared mutability, cyclic mutability and complex data flow at zero runtime cost.
16 min · 3,737 words
Dynamic Packages for Free Pascal and Lazarus
The getlazarus.org maintainer announces the first release of full dynamic package support for the Free Pascal Compiler and Lazarus IDE, letting components and plugins be built as shared libraries and installed without rebuilding the IDE, and covers restrictions, runtime changes, IDE improvements and how to help.
5 min · 1,157 words
Superoptimizing an FPU Emulator
purplesyringa wanted a branch-free way to compute the lowest set bit of a float for a floating-point emulator library, and instead of hand-deriving it wrote a small superoptimizer that searched instruction sequences and found a surprisingly clever rewrite.
4 min · 974 words
Making all divisions slower to fix a bug in 0.000000000000000000542% of cases
The Futhark compiler blog explains how signed integer division by -1 of the most negative two's-complement integer is undefined behaviour in the C code Futhark generates, how the compiler now adds a branch to every signed division to handle that single case correctly, what that costs on contrived and real benchmarks, and why unsigned division avoids the overhead.
8 min · 1,822 words
Fun Extending the C Preprocessor
David Priver, who is writing his own C2Y compiler/interpreter/REPL, shows extensions he added to its C preprocessor, including __print() and __where() debugging builtins, a native __map() that replaces recursive macro hacks, and __VA_COUNT__ for counting variadic arguments.
5 min · 1,147 words
I can't use generic lambdas at compile-time, now what?
Braden Ganetsky follows up his 'Break MSVC and Clang' post with a deep dive into working around a Clang bug that blocks using generic lambdas in constant evaluation, explaining how he got a compile-time C++ technique to work on Clang 16 onward.
16 min · 3,598 words
the problem (communication between the compiler, the build system, and beyond)
An essay arguing that operating systems miss optimization opportunities because compilers, build systems, package managers, filesystems and schedulers do not share dependency and resource information, with C examples of whole-program optimization and ideas for deduplication, easier development and better scheduling if they communicated.
13 min · 2,988 words
PGO or not PGO this is the dilemma. Step 2Step 2: How it works
The second of Marco Tusa's three-part Percona series on profile-guided optimization explains how PGO works as a two-pass build: instrumented binaries record per-edge control-flow counters during a training workload, and the compiler then uses those counts for inlining, branch layout, hot/cold splitting and code ordering, which is why MySQL's MTR test suite transfers well as training data.
5 min · 1,174 words
A hands-on tour of go build -toolexec: how the go command invokes the compiler, assembler and linker, and how to time, rewrite and instrument every run, from a simple stopwatch to injecting packages via importcfg and keeping the build cache honest, as used by garble, Orchestrion and OpenTelemetry's otelc.
23 min · 5,364 words