Split interfaces to the glue layer and backend into different files

.gitignore

@@ -3,6 +3,7 @@
 src/cdxxx.c
 src/debtab.c
 src/dmd
+src/dmd_frontend
 src/ddmd
 src/dmd.conf
 src/elxxx.c
@@ -18,6 +19,7 @@ test/test_results
 *.obj
 src/idgen.exe
 src/dmd.exe
+src/dmd_frontend.exe
 src/optabgen.exe
 src/verstr.h
 *.map

src/aggregate.d

@@ -11,7 +11,7 @@ module ddmd.aggregate;
 import core.stdc.stdio;
 import ddmd.access;
 import ddmd.arraytypes;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.clone;
 import ddmd.dclass;
 import ddmd.declaration;

src/arraytypes.d

@@ -9,7 +9,7 @@
 module ddmd.arraytypes;
 
 import ddmd.aggregate;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.dclass;
 import ddmd.declaration;
 import ddmd.dmodule;

src/backend.d

@@ -8,33 +8,14 @@
 
 module ddmd.backend;
 
-import ddmd.aggregate;
-import ddmd.dmodule;
-import ddmd.dscope;
-import ddmd.expression;
-import ddmd.lib;
-import ddmd.mtype;
-import ddmd.root.file;
-
 struct Symbol;
 struct code;
 struct block;
 struct Blockx;
 struct elem;
 
-extern extern (C++) void backend_init();
-extern extern (C++) void backend_term();
-extern extern (C++) void obj_start(char* srcfile);
-extern extern (C++) void obj_end(Library library, File* objfile);
-extern extern (C++) void obj_write_deferred(Library library);
-
-extern extern (C++) void genObjFile(Module m, bool multiobj);
-
-extern extern (C++) Symbol* toInitializer(AggregateDeclaration sd);
-
 // type.h
 
-
 alias tym_t = uint;
 alias mangle_t = ubyte;
 alias targ_size_t = ulong;

src/dclass.d

@@ -11,7 +11,7 @@ module ddmd.dclass;
 import core.stdc.string;
 import ddmd.aggregate;
 import ddmd.arraytypes;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.clone;
 import ddmd.declaration;
 import ddmd.dmodule;

src/denum.d

@@ -10,7 +10,7 @@ module ddmd.denum;
 
 import core.stdc.stdio;
 import ddmd.access;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.declaration;
 import ddmd.dmodule;
 import ddmd.doc;

src/dmodule.d

@@ -13,7 +13,7 @@ import core.stdc.stdlib;
 import core.stdc.string;
 import ddmd.aggregate;
 import ddmd.arraytypes;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.dimport;
 import ddmd.dmacro;
 import ddmd.doc;

src/dstruct.d

@@ -11,7 +11,7 @@ module ddmd.dstruct;
 import ddmd.aggregate;
 import ddmd.argtypes;
 import ddmd.arraytypes;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.clone;
 import ddmd.declaration;
 import ddmd.dmodule;

src/dsymbol.d

@@ -15,7 +15,7 @@ import ddmd.aggregate;
 import ddmd.aliasthis;
 import ddmd.arraytypes;
 import ddmd.attrib;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.dclass;
 import ddmd.declaration;
 import ddmd.denum;

src/dtemplate.d

@@ -15,7 +15,7 @@ import ddmd.aggregate;
 import ddmd.aliasthis;
 import ddmd.arraytypes;
 import ddmd.attrib;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.dcast;
 import ddmd.dclass;
 import ddmd.declaration;

src/expression.d

@@ -19,7 +19,7 @@ import ddmd.argtypes;
 import ddmd.arrayop;
 import ddmd.arraytypes;
 import ddmd.attrib;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.canthrow;
 import ddmd.clone;
 import ddmd.complex;

src/func.d

@@ -13,7 +13,7 @@ import core.stdc.string;
 import ddmd.aggregate;
 import ddmd.arraytypes;
 import ddmd.attrib;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.builtin;
 import ddmd.ctfeexpr;
 import ddmd.dclass;
@@ -48,8 +48,6 @@ import ddmd.target;
 import ddmd.tokens;
 import ddmd.visitor;
 
-extern extern (C++) RET retStyle(TypeFunction tf);
-
 enum ILS : int
 {
     ILSuninitialized,       // not computed yet

src/gluelayer.d

@@ -0,0 +1,121 @@
+// Compiler implementation of the D programming language
+// Copyright (c) 1999-2015 by Digital Mars
+// All Rights Reserved
+// written by Walter Bright
+// http://www.digitalmars.com
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+module ddmd.gluelayer;
+
+import ddmd.aggregate;
+import ddmd.dmodule;
+import ddmd.dscope;
+import ddmd.dsymbol;
+import ddmd.expression;
+import ddmd.lib;
+import ddmd.mtype;
+import ddmd.statement;
+import ddmd.root.file;
+
+version (NoBackend)
+{
+    struct Symbol;
+    struct code;
+    struct block;
+    struct Blockx;
+    struct elem;
+    struct TYPE;
+    alias type = TYPE;
+
+    // tocsym
+
+    extern (C++) Symbol* toInitializer(AggregateDeclaration ad)
+    {
+        return null;
+    }
+
+    // glue
+
+    extern (C++) void obj_write_deferred(Library library)
+    {
+    }
+
+    extern (C++) void obj_start(char* srcfile)
+    {
+    }
+
+    extern (C++) void obj_end(Library library, File* objfile)
+    {
+    }
+
+    extern (C++) void genObjFile(Module m, bool multiobj)
+    {
+    }
+
+    // msc
+
+    extern (C++) void backend_init()
+    {
+    }
+
+    extern (C++) void backend_term()
+    {
+    }
+
+    // iasm
+
+    extern (C++) Statement asmSemantic(AsmStatement s, Scope* sc)
+    {
+        assert(0);
+    }
+
+    // toir
+
+    extern (C++) RET retStyle(TypeFunction tf)
+    {
+        return RETregs;
+    }
+
+    extern (C++) void toObjFile(Dsymbol ds, bool multiobj)
+    {
+    }
+
+    version (OSX)
+    {
+        extern(C++) void objc_initSymbols()
+        {
+        }
+    }
+}
+else
+{
+    import ddmd.backend;
+
+    alias Symbol = ddmd.backend.Symbol;
+    alias code = ddmd.backend.code;
+    alias block = ddmd.backend.block;
+    alias Blockx = ddmd.backend.Blockx;
+    alias elem = ddmd.backend.elem;
+    alias type = ddmd.backend.type;
+
+    extern extern (C++) Symbol* toInitializer(AggregateDeclaration sd);
+
+    extern extern (C++) void obj_write_deferred(Library library);
+    extern extern (C++) void obj_start(char* srcfile);
+    extern extern (C++) void obj_end(Library library, File* objfile);
+    extern extern (C++) void genObjFile(Module m, bool multiobj);
+
+    extern extern (C++) void backend_init();
+    extern extern (C++) void backend_term();
+
+    extern extern (C++) Statement asmSemantic(AsmStatement s, Scope* sc);
+
+    extern extern (C++) RET retStyle(TypeFunction tf);
+    extern extern (C++) void toObjFile(Dsymbol ds, bool multiobj);
+
+    version (OSX)
+    {
+        extern(C++) void objc_initSymbols();
+    }
+}

src/mars.d

@@ -16,7 +16,7 @@ import core.stdc.stdio;
 import core.stdc.stdlib;
 import core.stdc.string;
 import ddmd.arraytypes;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.builtin;
 import ddmd.cond;
 import ddmd.dinifile;

src/mtype.d

@@ -22,7 +22,7 @@ import ddmd.aliasthis;
 import ddmd.argtypes;
 import ddmd.arraytypes;
 import ddmd.attrib;
-import ddmd.backend;
+import ddmd.gluelayer;
 import ddmd.complex;
 import ddmd.ctfeexpr;
 import ddmd.dcast;

src/objc.d

@@ -18,14 +18,13 @@ import ddmd.dstruct;
 import ddmd.expression;
 import ddmd.func;
 import ddmd.globals;
+import ddmd.gluelayer;
 import ddmd.id;
 import ddmd.identifier;
 import ddmd.mtype;
 import ddmd.root.outbuffer;
 import ddmd.root.stringtable;
 
-extern(C++) void objc_initSymbols();
-
 struct ObjcSelector
 {
     // MARK: Selector