+-- EZY: This code is very dodgy, 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). Thus, this is all one giant no-op. What we are
+-- actually interested in is saving are the non-system registers, which
+-- we is what the old code generator actually does at this point.
+-- Unfortunately, we can't do that here either, because we don't
+-- liveness information, and thus there's not an easy way to tell which
+-- specific global registers need to be saved (the 'vols' argument in
+-- the old code generator.) One possible hack is to save all of them
+-- unconditionally, but unless we have very clever dead /memory/
+-- elimination (unlikely), this will still leave a dead, unnecessary
+-- memory assignment. And really, we shouldn't be doing the workaround
+-- at this point in the pipeline, see Note [Register parameter passing].
+-- Right now the workaround is to avoid inlining across unsafe foreign
+-- calls in rewriteAssignments.