[Bug middle-end/70047] New: Warn on inefficient function parameter passing

["jaak at ristioja dot ee" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70047

            Bug ID: 70047
           Summary: Warn on inefficient function parameter passing
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jaak at ristioja dot ee
  Target Milestone: ---

According to the x86_64 ABI [1], function arguments are passed using registers
and stack memory. It might be useful for x86_64 and other architectures if GCC
would provide an option to warn if some parameters would (inefficiently) be
passed on the stack instead of being passed via registers. This would help
programmers optimize function signatures without disassembling the end result. 

Depending on the cost of different argument passing techniques in the ABI used,
this warning option could benefit from multiple levels or suboptions, e.g.

  -Wparameter-passing=memory,xmm

would warn if parameters are passed on stack or via xmm registers.


Just a raw idea. :)


[1] System V Application Binary Interface. AMD64 Architecture Processor
Supplement. Draft Version 0.99.6. http://www.x86-64.org/documentation/abi.pdf