Added generation of the llvm 'sret' parameter attribute where applicable.

Fixed some wrong argument handling code when setting parameter attributes.
Updated the tango unittest script in the tango patch, does not work yet, all modules don't compile...

gen/tocall.cpp

@@ -213,6 +213,13 @@ DValue* DtoCallFunction(Loc& loc, Type* resulttype, DValue* fnval, Expressions*
     LLFunctionType::param_iterator argbegin = callableTy->param_begin();
     LLFunctionType::param_iterator argiter = argbegin;
 
+    // parameter attributes
+    llvm::PAListPtr palist;
+
+    // return attrs
+    if (tf->llvmRetAttrs)
+        palist = palist.addAttr(0, tf->llvmRetAttrs);
+
     // handle implicit arguments
     std::vector<LLValue*> args;
 
@@ -222,6 +229,7 @@ DValue* DtoCallFunction(Loc& loc, Type* resulttype, DValue* fnval, Expressions*
         LLValue* retvar = new llvm::AllocaInst(argiter->get()->getContainedType(0), ".rettmp", gIR->topallocapoint());
         ++argiter;
         args.push_back(retvar);
+        palist = palist.addAttr(1, llvm::ParamAttr::StructRet);
     }
 
     // then comes a context argument...
@@ -261,10 +269,6 @@ DValue* DtoCallFunction(Loc& loc, Type* resulttype, DValue* fnval, Expressions*
     }
 
     // handle the rest of the arguments based on param passing style
-    llvm::PAListPtr palist;
-
-    if (tf->llvmRetAttrs)
-        palist = palist.addAttr(0, tf->llvmRetAttrs);
 
     // variadic instrinsics need some custom casts
     if (va_intrinsic)
@@ -296,7 +300,7 @@ DValue* DtoCallFunction(Loc& loc, Type* resulttype, DValue* fnval, Expressions*
             Argument* fnarg = Argument::getNth(tf->parameters, i);
             DValue* argval = DtoArgument(fnarg, (Expression*)arguments->data[i]);
             LLValue* arg = argval->getRVal();
-            if (fnarg)
+            if (fnarg) // can fnarg ever be null in this block?
             {
                 if (arg->getType() != callableTy->getParamType(j))
                     arg = DtoBitCast(arg, callableTy->getParamType(j));