f384938a10
The recent work in #4061 introduced a notion of "unique uses" for CLIF values that both simplified the load-op merging rules and allowed loads to merge in some more places. Unfortunately there's one factor that PR didn't account for: a unique use at the CLIF level could become a multiple-use at the VCode level, when a lowering uses a value multiple times! Making this less error-prone in general is hard, because we don't know the lowering in VCode until it's emitted, so we can't ahead-of-time know that a value will be used multiple times and prevent its merging. But we *can* know in the lowerings themselves when we're doing this. At least we get a panic from regalloc when we get this wrong; no bad code (uninitialized register being read) should ever come from a backend bug like this. This is still a bit less than ideal, but for now the fix is: in `cmp_and_choose` in the x64 backend (which compares values, then picks one or the other with a cmove), explicitly put values in registers. Fixes #4067 (thanks @Mrmaxmeier for the report!).
This crate contains the core Cranelift code generator. It translates code from an intermediate representation into executable machine code.