Use Module::members -> Dsymbol::codegen to define symbols.

This commit fundamentally changes the way symbol emission in
LDC works: Previously, whenever a declaration was used in some
way, the compiler would check whether it actually needs to be
defined in the currently processed module, based only on the
symbol itself. This lack of contextual information proved to
be a major problem in correctly handling emission of templates
(see e.g. #454).

Now, the DtoResolve…() family of functions and similar only
ever declare the symbols, and definition is handled by doing
a single pass over Module::members for the root module. This
is the same strategy that DMD uses as well, which should
also reduce the maintainance burden down the road (which is
important as during the last few releases, there was pretty
much always a symbol emission related problem slowing us
down).

Our old approach might have been a bit better tuned w.r.t.
avoiding emission of unneeded template instances, but 2.064
will bring improvements here (DMD: FuncDeclaration::toObjFile).
Barring such issues, the change shoud also marginally improve
compile times because of declarations no longer being emitted
when they are not needed.

In the future, we should also consider refactoring the code
so that it no longer directly accesses Dsymbol::ir but uses
wrapper functions that ensure that the appropriate
DtoResolve…() function has been called.

GitHub: Fixes #454.

gen/classes.cpp

@@ -35,24 +35,21 @@
 
 void DtoResolveClass(ClassDeclaration* cd)
 {
-    // make sure the base classes are processed first
-    ArrayIter<BaseClass> base_iter(cd->baseclasses);
-    while (base_iter.more())
-    {
-        BaseClass* bc = base_iter.get();
-        if (bc)
-        {
-            bc->base->codegen(Type::sir);
-        }
-        base_iter.next();
-    }
-
     if (cd->ir.resolved) return;
     cd->ir.resolved = true;
 
     Logger::println("DtoResolveClass(%s): %s", cd->toPrettyChars(), cd->loc.toChars());
     LOG_SCOPE;
 
+    // make sure the base classes are processed first
+    ArrayIter<BaseClass> base_iter(cd->baseclasses);
+    while (base_iter.more())
+    {
+        BaseClass* bc = base_iter.get();
+        DtoResolveClass(bc->base);
+        base_iter.next();
+    }
+
     // make sure type exists
     DtoType(cd->type);
 
@@ -73,11 +70,6 @@ void DtoResolveClass(ClassDeclaration* cd)
         }
     }
 
-    bool needs_def = mustDefineSymbol(cd);
-
-    // emit the ClassZ symbol
-    LLGlobalVariable* ClassZ = irAggr->getClassInfoSymbol();
-
     // emit the interfaceInfosZ symbol if necessary
     if (cd->vtblInterfaces && cd->vtblInterfaces->dim > 0)
         irAggr->getInterfaceArraySymbol(); // initializer is applied when it's built
@@ -87,43 +79,6 @@ void DtoResolveClass(ClassDeclaration* cd)
     {
         irAggr->initializeInterface();
     }
-    else
-    {
-        // emit the initZ symbol
-        LLGlobalVariable* initZ = irAggr->getInitSymbol();
-        // emit the vtblZ symbol
-        LLGlobalVariable* vtblZ = irAggr->getVtblSymbol();
-
-        // perform definition
-        if (needs_def)
-        {
-            // set symbol initializers
-            initZ->setInitializer(irAggr->getDefaultInit());
-            vtblZ->setInitializer(irAggr->getVtblInit());
-        }
-    }
-
-    // emit members
-    if (cd->members)
-    {
-        ArrayIter<Dsymbol> it(*cd->members);
-        while (!it.done())
-        {
-            Dsymbol* member = it.get();
-            if (member)
-                member->codegen(Type::sir);
-            it.next();
-        }
-    }
-
-    if (needs_def)
-    {
-        // emit typeinfo
-        DtoTypeInfoOf(cd->type);
-
-        // define classinfo
-        ClassZ->setInitializer(irAggr->getClassInfoInit());
-    }
 }
 
 //////////////////////////////////////////////////////////////////////////////////////////
@@ -131,7 +86,7 @@ void DtoResolveClass(ClassDeclaration* cd)
 DValue* DtoNewClass(Loc loc, TypeClass* tc, NewExp* newexp)
 {
     // resolve type
-    tc->sym->codegen(Type::sir);
+    DtoResolveClass(tc->sym);
 
     // allocate
     LLValue* mem;
@@ -143,7 +98,7 @@ DValue* DtoNewClass(Loc loc, TypeClass* tc, NewExp* newexp)
     // custom allocator
     else if (newexp->allocator)
     {
-        newexp->allocator->codegen(Type::sir);
+        DtoResolveDsymbol(newexp->allocator);
         DFuncValue dfn(newexp->allocator, newexp->allocator->ir.irFunc->func);
         DValue* res = DtoCallFunction(newexp->loc, NULL, &dfn, newexp->newargs);
         mem = DtoBitCast(res->getRVal(), DtoType(tc), ".newclass_custom");
@@ -184,7 +139,7 @@ DValue* DtoNewClass(Loc loc, TypeClass* tc, NewExp* newexp)
     {
         Logger::println("Calling constructor");
         assert(newexp->arguments != NULL);
-        newexp->member->codegen(Type::sir);
+        DtoResolveDsymbol(newexp->member);
         DFuncValue dfn(newexp->member, newexp->member->ir.irFunc->func, mem);
         return DtoCallFunction(newexp->loc, tc, &dfn, newexp->arguments);
     }
@@ -197,7 +152,7 @@ DValue* DtoNewClass(Loc loc, TypeClass* tc, NewExp* newexp)
 
 void DtoInitClass(TypeClass* tc, LLValue* dst)
 {
-    tc->sym->codegen(Type::sir);
+    DtoResolveClass(tc->sym);
 
     uint64_t n = tc->sym->structsize - Target::ptrsize * 2;
 
@@ -365,8 +320,8 @@ DValue* DtoDynamicCastObject(DValue* val, Type* _to)
     // call:
     // Object _d_dynamic_cast(Object o, ClassInfo c)
 
-    ClassDeclaration::object->codegen(Type::sir);
-    ClassDeclaration::classinfo->codegen(Type::sir);
+    DtoResolveClass(ClassDeclaration::object);
+    DtoResolveClass(ClassDeclaration::classinfo);
 
     llvm::Function* func = LLVM_D_GetRuntimeFunction(gIR->module, "_d_dynamic_cast");
     LLFunctionType* funcTy = func->getFunctionType();
@@ -378,7 +333,7 @@ DValue* DtoDynamicCastObject(DValue* val, Type* _to)
 
     // ClassInfo c
     TypeClass* to = static_cast<TypeClass*>(_to->toBasetype());
-    to->sym->codegen(Type::sir);
+    DtoResolveClass(to->sym);
 
     LLValue* cinfo = to->sym->ir.irAggr->getClassInfoSymbol();
     // unfortunately this is needed as the implementation of object differs somehow from the declaration
@@ -428,8 +383,8 @@ DValue* DtoDynamicCastInterface(DValue* val, Type* _to)
     // call:
     // Object _d_interface_cast(void* p, ClassInfo c)
 
-    ClassDeclaration::object->codegen(Type::sir);
-    ClassDeclaration::classinfo->codegen(Type::sir);
+    DtoResolveClass(ClassDeclaration::object);
+    DtoResolveClass(ClassDeclaration::classinfo);
 
     llvm::Function* func = LLVM_D_GetRuntimeFunction(gIR->module, "_d_interface_cast");
     LLFunctionType* funcTy = func->getFunctionType();
@@ -440,7 +395,7 @@ DValue* DtoDynamicCastInterface(DValue* val, Type* _to)
 
     // ClassInfo c
     TypeClass* to = static_cast<TypeClass*>(_to->toBasetype());
-    to->sym->codegen(Type::sir);
+    DtoResolveClass(to->sym);
     LLValue* cinfo = to->sym->ir.irAggr->getClassInfoSymbol();
     // unfortunately this is needed as the implementation of object differs somehow from the declaration
     // this could happen in user code as well :/
@@ -623,7 +578,7 @@ static LLConstant* build_class_dtor(ClassDeclaration* cd)
     if (!dtor)
         return getNullPtr(getVoidPtrType());
 
-    dtor->codegen(Type::sir);
+    DtoResolveDsymbol(dtor);
     return llvm::ConstantExpr::getBitCast(dtor->ir.irFunc->func, getPtrToType(LLType::getInt8Ty(gIR->context())));
 }