Merging ten pull requests into submain in a single day signifies a turning point for Cx. We're talking about the JIT backend making a leap from theoretical to tangible execution. This involved delivering the first real JIT-compiled arithmetic and memory operations using Cranelift, among other things. If you’ve been following the backend development, today’s progress might get you nodding along with me.
First Real JIT Execution
If you’ve ever stared at a scaffold and wondered whether it’ll hold when it all comes together, the journey of CX-25 is a familiar one. PR #78 took the skeleton of HostBoundary::execute and fleshed it out into a functioning Cranelift JIT pipeline. Now, Cx can compile arithmetic operations like iadd, isub, and imul, right up to returning a result. We added nine integration tests to make sure the holistic structure is sound. This marks the first time Cx programs produce correct results through the Cranelift path, handing the baton to stack operations in CX-26.
PR #79 extended this by introducing stack memory support, implementing Alloca, load, and store, facilitating byte-specific operations that dare not step on each other’s toes. With these foundational pieces falling into place, the JIT path is no longer just a potential, but a lever we can pull on.
CX-41 swept in to patch a hole left by PR CX-27. It brought Jump and Branch into the action with proper testing, turning failure into a collection of 11 successful cases.
Runtime Intrinsics Boundary
In CX-35, PR #86 did more than just audit. It defined a clear boundary for built-in operations. This means a UnsupportedSemanticConstruct is the new sheriff in town when encountering unsupported semantics in lower.rs. What follows are the seeds of a plan ready to sprout in CX-38, setting a framework where intrinsics can be reality-checked via compilation declarations and Cranelift import binding. The implications? For starters, the first visible output through JIT by putting printn into action.
Loop Variable Safety Ensured
Loops, those repetitive workhorses, got a security upgrade with CX-40. By marking loop variables as read-only, Cx has shifted towards safety, dispatching pitfalls of inadvertent reassignment. The IR validator is now tighter with logic to back up this guarantee. It’s a fundamental protection, now formally supported at the IR level.
Elsewhere, CX-37 sets the stake for expression evaluation order, a subtle yet vital aspect of concurrent code complexity. Left-to-right rules govern not just mathematical logic but how computations intertwine with print sequences.
Catching Up and Moving Forward
The sweep through CX-21 to CX-24 brought the previous day’s pipeline promises to life. From method call errors to lowering and boundary groundwork, these pieces laid a foundation that today’s leap depended on. Though submain diverges with new code shadows expanding from the ever-pursuing main tip, the resolve remains: keep merging and advancing.
As we stand on the crest of what's been done, a tidal wave of reviews awaits. PRs across phases hold keys to unleashing Cx's potential—covering arithmetic, functions, pointers, and beyond. Syncing submain and main becomes crucial each time the backlog clears this threshold. We didn’t touch Phase 11 or the elusive string layout questions today, but it's an orchestra in progress. Harmony lies in our evolving capability to build on momentum.
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Originally published at https://cx-lang.com/blog/2026-05-06