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[Bug c/70955] New: regression in code generation for __builtin_ms_va_list in GCC 6.1


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70955

            Bug ID: 70955
           Summary: regression in code generation for __builtin_ms_va_list
                    in GCC 6.1
           Product: gcc
           Version: 6.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zenith432 at users dot sourceforge.net
  Target Milestone: ---

I've tried on GCC 6.1.0 built for OS X, and GCC 6.1.1 on Fedora 23 supplied by
their rawhide.  Same behavior.

- variadic function with x86-64 ms_abi calling convention.
- defines local variable of type __builtin_ms_va_list.
- iterates with __builtin_va_arg (note: there is no corresponding
__builtin_ms_va_arg).
- __builtin_va_arg treats the __builtin_ms_va_list variable as a sysv va_list,
and goes berserk.

I've anaylzed this by looking at the code generated.

Same wrong code generated if __builtin_va_list is used inside an ms_abi
function instead of __builtin_ms_va_list.

This functionality worked on both GCC 5.3 and GCC 4.9, so this is a regression.
 I've compared the resulting code generated to GCC 5.3.  The code generated on
GCC 5.3 is good.

As mentioned above, there is no __builtin_ms_va_arg, and never was.  The
function __builtin_va_arg has previously been used to iterate on all types of
__builtin_*_va_list.

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