ed9db962de
The current lowering helper for `cmpxchg` returns the literal RealReg `rax` as its result. However, this breaks a number of invariants, and eventually causes a regalloc panic if used as a blockparam arg (pinned vregs cannot be used in this way). In general we have to return regular vregs, not a RealReg, as results of instructions during lowering. However #4223 added a helper for `x64_cmpxchg` that returns a literal `rax`. Fortunately we can do the right thing here by just giving a fresh vreg to the instruction; the regalloc constraints mean that this vreg is constrained to `rax` at the instruction (at its def/late point), so the generator of the instruction need not worry about `rax` here.
This crate contains the core Cranelift code generator. It translates code from an intermediate representation into executable machine code.