[patch i386]: Prevent to assume for 64-bit ms-abi that DX_REG is used as function-value

[Kai Tietz]

Hello,

this patch fixes a nit detected in ix86_function_value_regno_p.  For
x64 ms-abi we don't have DX_REG-register as valid function-value
register.

ChangeLog

2014-06-03  Kai Tietz  <kti...@redhat.com>

        * config/i386/i386.c (ix86_function_value_regno_p): Disallow DX_REG for
        64-bit ms-abi.

Tested for x86_64-w64-mingw32, and x86_64-unknown-linux-gnu.  If there
are no objections I will commit that patch tomorrow.

Regards,
Kai

Index: i386.c
===================================================================
--- i386.c      (Revision 211198)
+++ i386.c      (Arbeitskopie)
@@ -7775,7 +7775,7 @@ ix86_function_value_regno_p (const unsigned int r
     {
     case AX_REG:
     case DX_REG:
-      return true;
+      return (regno != DX_REG || !TARGET_64BIT || ix86_abi != MS_ABI);
     case DI_REG:
     case SI_REG:
       return TARGET_64BIT && ix86_abi != MS_ABI;