[m-dev.] GCC back-end: fix some omissions in mlds_to_gcc.m

[Fergus Henderson]

Estimated hours taken: 0.75

compiler/mlds_to_gcc.m:
	Fix a couple of bugs / unimplemented features:
	- handle pointers to functions with no (i.e. void) return type
	- handle the references to `private_builtin:dummy_word'
	  that the MLDS code generator generates
	With these changes, the GCC back-end now builds `samples/diff'
	and passes the tests in samples/tests/diff.

Workspace: /home/hg/fjh/gcc-cvs/gcc/mercury
Index: compiler/mlds_to_gcc.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/mlds_to_gcc.m,v
retrieving revision 1.21
diff -u -d -r1.21 mlds_to_gcc.m
--- compiler/mlds_to_gcc.m	2001/01/18 15:43:42	1.21
+++ compiler/mlds_to_gcc.m	2001/01/18 16:21:16
@@ -1794,7 +1794,9 @@
 build_type(mlds__func_type(Params), _, GlobalInfo, GCC_FuncPtrType) -->
 	{ Signature = mlds__get_func_signature(Params) },
 	{ Signature = mlds__func_signature(ArgTypes, RetTypes) },
-	( { RetTypes = [RetType] } ->
+	( { RetTypes = [] } ->
+		{ GCC_RetType = gcc__void_type_node }
+	; { RetTypes = [RetType] } ->
 		build_type(RetType, no_size, GlobalInfo, GCC_RetType)
 	;
 		{ sorry(this_file, "multiple return types") }
@@ -2967,13 +2969,24 @@
 	->
 		{ Expr = gcc__var_expr(GlobalVarDecl) }
 	;
-		% check if its in the private_builtin module
+		% check if it's in the private_builtin module
 		% and is an RTTI enumeration constant
 		{ mercury_private_builtin_module(PrivateBuiltin) },
 		{ mercury_module_name_to_mlds(PrivateBuiltin) = ModuleName },
 		{ rtti_enum_const(VarName, IntVal) }
 	->
 		gcc__build_int(IntVal, Expr)
+	;
+		% check if it's private_builtin:dummy_var
+		{ mercury_private_builtin_module(PrivateBuiltin) },
+		{ mercury_module_name_to_mlds(PrivateBuiltin) = ModuleName },
+		{ VarName = "dummy_var" }
+	->
+		% if so, generate an extern declaration for it, and use that.
+		{ GCC_VarName = build_data_var_name(ModuleName, var(VarName)) },
+		{ Type = 'MR_Word' },
+		gcc__build_extern_var_decl(GCC_VarName, Type, Decl),
+		{ Expr = gcc__var_expr(Decl) }
 	;
 		{ unexpected(this_file, "undeclared variable: " ++
 			build_qualified_name(Name)) }

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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