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rev 5188 : 8024344: PPC64 (part 112): C argument in register AND stack slot.
Summary: On PPC, the first 13 floating point arguments to C calls are passed in floating point registers. Also, all but the first 8 arguments are passed on the stack. So there can be floating point arguments that are passed on the stack and in a register. We duplicate the regs datastructure in c_calling_convention() to represent this.

@@ -354,11 +354,19 @@
   static void check_member_name_argument_is_last_argument(methodHandle method,
                                                           const BasicType* sig_bt,
                                                           const VMRegPair* regs) NOT_DEBUG_RETURN;
   // Ditto except for calling C
-  static int c_calling_convention(const BasicType *sig_bt, VMRegPair *regs, int total_args_passed);
+  //
+  // C argument in register AND stack slot.
+  // Some architectures require that an argument must be passed in a register
+  // AND in a stack slot. These architectures provide a second VMRegPair array
+  // to be filled by the c_calling_convention method. On other architectures,
+  // NULL is being passed as the second VMRegPair array, so arguments are either
+  // passed in a register OR in a stack slot.
+  static int c_calling_convention(const BasicType *sig_bt, VMRegPair *regs, VMRegPair *regs2,
+                                  int total_args_passed);
   // Generate I2C and C2I adapters. These adapters are simple argument marshalling
   // blobs. Unlike adapters in the tiger and earlier releases the code in these
   // blobs does not create a new frame and are therefore virtually invisible
   // to the stack walking code. In general these blobs extend the callers stack