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Language-level guarantees---like module runtime isolation for WebAssembly (Wasm)---are only as strong as the compiler that produces a final, native-machine-specific executable. The process of lowering language-level constructions to ISA-specific instructions can introduce subtle bugs that violate security guarantees. In this paper, we present Crocus, a system for lightweight, modular verification of instruction-lowering rules within Cranelift, a production retargetable Wasm native code generator. We use Crocus to verify lowering rules that cover WebAssembly 1.0 support for integer operations in the ARM aarch64 backend. We show that Crocus can reproduce 3 known bugs (including a 9.9/10 severity CVE), identify 2 previously-unknown bugs and an underspecified compiler invariant, and help analyze the root causes of a new bug. 

Applications targeting digital signal processors (DSPs) benefit from fast implementations of small linear algebra kernels. While existing auto-vectorizing compilers are effective at extracting performance from large kernels, they struggle to invent the complex data movements necessary to optimize small kernels. To get the best performance, DSP engineers must hand-write and tune specialized small kernels for a wide spectrum of applications and architectures. We present Diospyros, a search-based compiler that automatically finds efficient vectorizations and data layouts for small linear algebra kernels. Diospyros combines symbolic evaluation and equality saturation to vectorize computations with irregular structure. We show that a collection of Diospyros-compiled kernels outperform implementations from existing DSP libraries by 3.1× on average, that Diospyros can generate kernels that are competitive with expert-tuned code, and that optimizing these small kernels offers end-to-end speedup for a DSP application.