835db11bea
As part of a Wasm JIT update, SpiderMonkey is changing its internal WebAssembly function ABI. The new ABI's frame format includes "caller TLS" and "callee TLS" slots. The details of where these come from are not important; from Cranelift's point of view, the only relevant requirement is that we have two on-stack args that are always present (offsetting other on-stack args), and that we define special argument purposes so that we can supply values for these slots. Note that this adds a *new* ABI (a variant of the Baldrdash ABI) because we do not want to tightly couple the landing of this PR to the landing of the changes in SpiderMonkey; it's better if both the old and new behavior remain available in Cranelift, so SpiderMonkey can continue to vendor Cranelift even if it does not land (or backs out) the ABI change. Furthermore, note that this needs to be a Cranelift-level change (i.e. cannot be done purely from the translator environment implementation) because the special TLS arguments must always go on the stack, which would not otherwise happen with the usual argument-placement logic; and there is no primitive to push a value directly in CLIF code (the notion of a stack frame is a lower-level concept).
This crate contains the metaprogram used by cranelift-codegen. It's not useful on its own.