May 2026: WASM RyuJIT stability and performance improvements in dotnet/runtime; JIT parameter handling optimization for GS frames (Windows AMD64); deterministic funclet ordering for Wasm EH clauses; and host tooling enhancement via length-prefixing JIT code contributions to facilitate host extraction without parsing.

April 2026 (2026-04) performance summary for dotnet/runtime focusing on JIT and Wasm RyuJIT improvements, reliability fixes, and cross-platform capabilities. Highlights include significant feature deliveries, targeted bug fixes, and tangible optimization opportunities that drive performance and stability for production workloads.

March 2026 highlights include delivering WebAssembly/WasmJIT compiler improvements with loop-aware RPO, enhanced debugging, and robust overflow/null checks; implementing Wasm EH flow to support resuming after exceptions; enabling crossgen2 support for Wasm RyuJit via a JIT config; substantial core data structure refactoring and safety improvements (encapsulation of BasicBlock and safe ArrayStack iterators); and improvements to unreachable block removal and related flow-graph safety in Wasm/RyuJIT. These efforts delivered measurable performance gains, reliability, better GC awareness, and clear business value for Wasm workloads.

February 2026 (2026-02) was focused on stabilizing Wasm RyuJit and JIT infrastructure across dotnet/runtime and filipnavara/runtime, delivering concrete codegen improvements, runtime capabilities, and maintainability enhancements that drive business value: more reliable Wasm workloads, faster iterations, and cleaner codepaths for future GS enablement. Key outcomes include robust Wasm codegen with write barriers and direct helper calls, corrected throw-path emission to avoid mid-block fall-through, Bitcast support, a standardized naming scheme for JIT compiler references, and localloc support for dynamic stack allocation in Wasm RyuJIT. Crossgen and codegen improvements further reduce bugs in debug/release scenarios and improve codegen resilience across platforms.

Month: 2026-01 | Repository: dotnet/runtime Overview: This month focused on strengthening Wasm/JIT codegen reliability and expanding capabilities for Wasm-based execution paths. We delivered foundational Wasm RyuJIT documentation and stack-arg groundwork, hardened emission correctness for block/label structures, extended analysis coverage, and laid groundwork for explicit throw helpers and null checks in Wasm. These changes improve correctness, test reliability, and pave the way for safer error handling and future performance optimizations. Key features delivered: - Wasm RyuJIT: Initial writeup on the calling convention (documentation of R2R/Was m path) — commit 2d5cde83. - Wasm RyuJIT: Wasm stack arg preliminaries — introduced SP as first arg and stack prelims for managed calling convention — commit 03b78171. - JIT: [Wasm RyuJIT] Fix emission of block and label instructions by preserving the type field — commit e2298d5c. - [RyuJit Wasm] fix off by one error for br_table — commit 32cae384. - [RyuJit Wasm] don't home locals if none are referenced — commit 4bab919a. - Wasm RyuJIT: Fix register homing behavior and related fixes — commits 4bab919a and 64506870. - JIT: Fix retyping issue in object stack allocation — commit 9cff6e92. - JIT: Remove anticipated demand for throw helpers — commit cb83a15a. - JIT: JIT: Extend CEA to handle a few more cases (GetEnumerator return path) — commit c21ca88d. - Wasm RyuJIT: Throw helper / null check preliminaries — commit 5c232659. - JIT: SpanHelpers.Fill may escape its last argument — commit 25a64f0b. Major bugs fixed: - Emission correctness: preserved type field for block/label emission in Wasm RyuJIT — e2298d5c54. - Br_table handling: off-by-one count fix for default target — 32cae3846c5e. - Local/home handling: avoid unwarranted home of locals when none referenced — 4bab919a412b. - Register homing: improved RyuJit Wasm register homing behavior — 64506870519e. - SpanHelpers: prevent escaping the last argument — 25a64f0b5847. - CEA coverage: extended to handle additional cases around GetEnumerator returns — c21ca88da77b. - Stack/object typing: prevent retyping during object stack allocations — 9cff6e925c8b. - Throw helper demand: removal of anticipated throw-helper signaling — cb83a15ab9921c53ef8d. - Throw helpers groundwork for Wasm: preliminary support and code-generation hooks — 5c2326596dc0b21583dbba5db9298c025eacbf64. Overall impact and accomplishments: - Reliability: Strengthened Wasm/JIT code paths, improving correctness for Wasm tests and replay scenarios (e.g., non-NYI fixes in Wasm tests). This reduces brittle test flakiness and supports more robust cross-plat Wasm execution. - Safety and correctness: Expanded analysis and codegen correctness, especially around object lifetime and enumerator handling, reducing silent escapes and type propagation bugs. - Readiness for future features: Groundwork laid for explicit Wasm throw helpers and null-check handling, and for more robust Wasm calling conventions; positions the team to implement explicit EH paths with predictable codegen. - Business value: Fewer regressions in Wasm/JIT codegen, enabling more reliable builds, faster integration cycles, and improved confidence in Wasm-based workloads. Technologies/skills demonstrated: - JIT engineering, Wasm-specific RyuJIT codegen, and crossgen considerations. - Stack frame layout and calling-convention handling in Wasm (SP-first argument, PE pointer handling). - Code emission correctness for blocks/labels and br_table switching. - Static analysis enhancements: Conditional Escape Analysis extensions. - Defensive programming around retyping, local lifetimes, and throw helper integration.

December 2025: Delivered WebAssembly backend improvements in RyuJIT for dotnet/runtime, enabling Wasm as a first-class target with improved performance and reliability. Implemented control-flow codegen, improved ABI handling for small argument types, and optimized switch emission and label management. Added support for NOT/NEG and direct 64-bit returns (TYP_LONG) in Wasm codegen, plus partial local store support to reflect Wasm stack semantics. Expanded runtime capabilities with dynamic, on-demand type loading when merging array types, increasing robustness of cross-type scenarios. Strengthened tooling and testing with Wasm SPMI target support and targeted fixes to bring-up tests and correctness gaps in unordered floating-point comparisons, improving reliability across Wasm workloads.

November 2025 performance-focused month for dotnet/runtime, centered on strengthening Wasm support in the JIT and hardening memory safety and build reliability. Delivered enhancements to Wasm control flow handling in the JIT, expanded codegen capabilities, and implemented safety/fix measures that improve stability, testability, and performance for Wasm workloads.

October 2025: Delivered performance, reliability, and tooling improvements for dotnet/runtime, focused on devirtualization, JIT robustness, tail-call correctness, and SuperPMI tooling. The work restored performance benefits for interface-based patterns, fixed critical JIT crash scenarios, and tightened CI/test tooling, delivering measurable business value through faster runtimes, higher stability, and more reliable test instrumentation.

September 2025: Focused on stabilizing the JIT pipeline, expanding profiling capabilities, and strengthening cross-platform/toolchain support. Delivered critical JIT LSRA crash fix on AVX-512 during VMR builds; corrected inline return value substitution for comma expressions with tests; upgraded the toolchain to enable /guard:cf on Windows and incorporated RISC-V enhancements; added instrumentation for inlinees during optimized JIT passes to gather profiling data; hardened PGO instrumentation by gating for tiering eligibility to avoid erroneous instrumentation under stress modes. These work items improve runtime reliability, build stability, performance insights, and cross-architecture readiness, driving business value in performance and reliability.

August 2025 performance and productivity overview for dotnet/runtime. The team delivered targeted JIT enhancements and stability fixes, expanded optimization coverage, and strengthened benchmarking and performance instrumentation. Key outcomes include more aggressive inlining opportunities, improved correctness and handling in JIT-compiled code, and more reliable performance measurements for release vs checked JIT comparisons.

July 2025 highlights for dotnet/runtime focused on JIT correctness, performance, and profiling fidelity across platforms. Key features delivered and major bugs fixed are summarized below, along with the overall business impact and the technologies demonstrated. Key features delivered: - JIT loop header optimization: removed unneeded keep flag, improving compilation efficiency for preheaders in loops with try-entries in the same EH region (#117227). - JIT conditional escape analysis: relaxed guard-condition resolution to allow GDV analysis to proceed even when resolved later in the cleanup pass (#117222). - JIT conditional escape analysis: enabled cloning when an allocation dominates an enumerator assignment and restored IEnumerable.GetEnumerator recognition to improve inlining (#117295). - JIT OSR inlining: extended IL size cap to preserve profiling data across final tiers, strengthening JIT effectiveness (#117816). Major bugs fixed: - JIT range-based optimization safety for non-integer constants: ensures integral types are used for comparison operands before range analysis to prevent incorrect optimizations (#117220). - JIT ARM: profiler leave hook correctly accounts for void returns, preventing inaccurate GC reporting during profiling (#117201). - JIT inlining policy: fixed regression by capping IL size at Tier1+Instr to avoid losing crucial profile data (#117492). - JIT robustness: guard assertion propagation tolerates missing class handles during optimization, preventing propagation errors (#117631). - JIT conditional escape analysis: refined handling under guarded calls with multiple enumerators to ensure correct stack/heap decisions and added tests (#118214). Overall impact and accomplishments: - Strengthened correctness and stability of JIT optimizations across platforms, including ARM, reducing miscompilations and GC reporting errors. - Improved performance through safer, more aggressive inlining and escape analysis, with better preservation of profiling data across OSR and final tiers. - Expanded test coverage for complex allocation and enumerator scenarios, contributing to longer-term reliability. Technologies/skills demonstrated: - JIT compiler internals: range-based optimizations, escape analysis, inlining policies, OSR. - Cross-platform profiling and GC integration (ARM-specific fixes). - IL size management and profiling data retention strategies. - Test-driven improvements with targeted regression tests and coverage for enumerator scenarios.

June 2025 performance month focused on delivering JIT/runtime optimizations and expanded profiling/diagnostics across two repositories. Key work improved allocation efficiency, enabled more aggressive inlining, broadened optimization opportunities, enhanced profiling data collection, and strengthened robustness and diagnostics. Delivered features and bug fixes in filipnavara/runtime and dotnet/runtime with clear business value in reduced allocations, improved throughput, and more reliable runtime behavior.

May 2025 — Performance and reliability update for filipnavara/runtime focused on JIT optimizations, GC-awareness, and test reliability. Key features delivered: - JIT: Run local assertion propagation in postorder during morph to enable more aggressive optimizations. - JIT: Use root compiler instance for sufficient PGO observation. - JIT: Arrays are now not always TYP_REF. - JIT: Escape analysis improvements (remember indir store addresses; refactoring). - JIT: Escape analysis and BLK layout improvements (gc-ness checks for GT_BLK, layout updates, retyping fixes, and delegation expansion).