[Bug c/89485] New: Support vectorcall calling convention on windows

[yyc1992 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89485

            Bug ID: 89485
           Summary: Support vectorcall calling convention on windows
           Product: gcc
           Version: 8.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: yyc1992 at gmail dot com
  Target Milestone: ---

I'm very surprised that I didn't find an issue for this so sorry if this is
discussed/rejected somewhere else.

It appears that both MSVC and clang supports a vectorcall calling convention
which is very similar to the one used on linux and passes large vectors in the
corresponding vector register instead of on the stack. It'll be nice if gcc can
support that both for efficiency and for compatibility.

Ref
https://docs.microsoft.com/en-us/cpp/cpp/vectorcall?view=vs-2017
https://clang.llvm.org/docs/AttributeReference.html#id335