e95ffe4413
* Fix StructReturn handling: properly mark the clobber, and offset actual rets. The legalization of `StructReturn` was causing issues in the new call-handling code: the `StructReturn` ret was included in the `SigData` as if it were an actual CLIF-level return value, but it is not. Prior to using regalloc constraints for return values, we unconditionally included rax (or the architecture's usual return register) as a def, so it would be properly handled as "clobbered" by the regalloc. With the new scheme, we include defs on the call only for CLIF-level outputs. Callees with `StructReturn` args were thus not known to clobber the return-value register, and values might be corrupted. This PR updates the code to include a `StructReturn` ret as a clobber rather than a returned value in the relevant spots. I observed it causing saves/restores of rax in some CLIF that @bjorn3 provided me, but I was having difficulty minimizing this into a test-case that I would be comfortable including as a precise-output case (including the whole thing verbatim would lock down a bunch of other irrelevant details and cause test-update noise later). If we can find a more minimized example I'm happy to include it as a filetest. Fixes #5018.
This crate contains the core Cranelift code generator. It translates code from an intermediate representation into executable machine code.