2986f6b0ff
* ABI: implement register arguments with constraints. Currently, Cranelift's ABI code emits a sequence of moves from physical registers into vregs at the top of the function body, one for every register-carried argument. For a number of reasons, we want to move to operand constraints instead, and remove the use of explicitly-named "pinned vregs"; this allows for better regalloc in theory, as it removes the need to "reverse-engineer" the sequence of moves. This PR alters the ABI code so that it generates a single "args" pseudo-instruction as the first instruction in the function body. This pseudo-inst defs all register arguments, and constrains them to the appropriate registers at the def-point. Subsequently the regalloc can move them wherever it needs to. Some care was taken not to have this pseudo-inst show up in post-regalloc disassemblies, but the change did cause a general regalloc "shift" in many tests, so the precise-output updates are a bit noisy. Sorry about that! A subsequent PR will handle the other half of the ABI code, namely, the callsite case, with a similar preg-to-constraint conversion. * Update based on review feedback. * Review feedback.
This crate contains the core Cranelift code generator. It translates code from an intermediate representation into executable machine code.