+--
+-- This code isn't actually used right now, because callerSaves
+-- only ever returns true in the current universe for registers NOT in
+-- system_regs (just do a grep for CALLER_SAVES in
+-- includes/stg/MachRegs.h). It's all one giant no-op, and for
+-- good reason: having to save system registers on every foreign call
+-- would be very expensive, so we avoid assigning them to those
+-- registers when we add support for an architecture.
+--
+-- Note that the old code generator actually does more work here: it
+-- also saves other global registers. We can't (nor want) to do that
+-- here, as we don't have liveness information. And really, we
+-- shouldn't be doing the workaround at this point in the pipeline, see
+-- Note [Register parameter passing] and the ToDo on CmmCall in
+-- cmm/CmmNode.hs. Right now the workaround is to avoid inlining across
+-- unsafe foreign calls in rewriteAssignments, but this is strictly
+-- temporary.