ldc/gen/toconstelem.cpp

//===-- toconstelem.cpp ---------------------------------------------------===//
//
//                         LDC – the LLVM D compiler
//
// This file is distributed under the BSD-style LDC license. See the LICENSE
// file for details.
//
//===----------------------------------------------------------------------===//

#include "gen/arrays.h"
#include "gen/classes.h"
#include "gen/complex.h"
#include "gen/irstate.h"
#include "gen/llvm.h"
#include "gen/llvmhelpers.h"
#include "gen/logger.h"
#include "gen/structs.h"
#include "gen/tollvm.h"
#include "ir/irtypeclass.h"
#include "ir/irtypestruct.h"

// Needs other includes.
#include "ctfe.h"

extern dinteger_t undoStrideMul(Loc& loc, Type* t, dinteger_t offset);

/// Emits an LLVM constant corresponding to the expression.
///
/// Due to the current implementation of AssocArrayLiteralExp::toElem, the
/// implementations have to be able to handle being called on expressions
/// that are not actually constant. In such a case, an LLVM undef of the
/// expected type should be returned (_not_ null).
class ToConstElemVisitor : public Visitor
{
    IRState *p;
    LLConstant *result;
public:

    ToConstElemVisitor(IRState *p_) : p(p_) { }

    // Import all functions from class Visitor
    using Visitor::visit;

    //////////////////////////////////////////////////////////////////////////////////////////

    LLConstant *toConstElem(Expression *e)
    {
        result = 0;
        e->accept(this);
        return result;
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(VarExp *e)
    {
        IF_LOG Logger::print("VarExp::toConstElem: %s @ %s\n", e->toChars(), e->type->toChars());
        LOG_SCOPE;

        if (SymbolDeclaration* sdecl = e->var->isSymbolDeclaration())
        {
            // this seems to be the static initialiser for structs
            Type* sdecltype = sdecl->type->toBasetype();
            IF_LOG Logger::print("Sym: type=%s\n", sdecltype->toChars());
            assert(sdecltype->ty == Tstruct);
            TypeStruct* ts = static_cast<TypeStruct*>(sdecltype);
            DtoResolveStruct(ts->sym);
            result = getIrAggr(ts->sym)->getDefaultInit();
            return;
        }

        if (TypeInfoDeclaration* ti = e->var->isTypeInfoDeclaration())
        {
            LLType* vartype = DtoType(e->type);
            result = DtoTypeInfoOf(ti->tinfo, false);
            if (result->getType() != getPtrToType(vartype))
                result = llvm::ConstantExpr::getBitCast(result, vartype);
            return;
        }

        VarDeclaration* vd = e->var->isVarDeclaration();
        if (vd && vd->isConst() && vd->init)
        {
            if (vd->inuse)
            {
                e->error("recursive reference %s", e->toChars());
                result = llvm::UndefValue::get(DtoType(e->type));
            }
            else
            {
                vd->inuse++;
                // return the initializer
                result = DtoConstInitializer(e->loc, e->type, vd->init);
                vd->inuse--;
            }
        }
        // fail
        else
        {
            e->error("non-constant expression %s", e->toChars());
            result = llvm::UndefValue::get(DtoType(e->type));
        }
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(IntegerExp *e)
    {
        IF_LOG Logger::print("IntegerExp::toConstElem: %s @ %s\n", e->toChars(), e->type->toChars());
        LOG_SCOPE;
        LLType* t = DtoType(e->type);
        if (isaPointer(t))
        {
            Logger::println("pointer");
            LLConstant* i = LLConstantInt::get(DtoSize_t(), (uint64_t)e->getInteger(), false);
            result = llvm::ConstantExpr::getIntToPtr(i, t);
        }
        else
        {
            assert(llvm::isa<LLIntegerType>(t));
            result = LLConstantInt::get(t, (uint64_t)e->getInteger(), !e->type->isunsigned());
            assert(result);
            IF_LOG Logger::cout() << "value = " << *result << '\n';
        }
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(RealExp *e)
    {
        IF_LOG Logger::print("RealExp::toConstElem: %s @ %s | %La\n", e->toChars(), e->type->toChars(), e->value);
        LOG_SCOPE;
        Type* t = e->type->toBasetype();
        result = DtoConstFP(t, e->value);
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(NullExp *e)
    {
        IF_LOG Logger::print("NullExp::toConstElem(type=%s): %s\n", e->type->toChars(), e->toChars());
        LOG_SCOPE;
        LLType* t = DtoType(e->type);
        if (e->type->ty == Tarray)
        {
            assert(isaStruct(t));
            result = llvm::ConstantAggregateZero::get(t);
        }
        else
        {
            result = LLConstant::getNullValue(t);
        }
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(ComplexExp *e)
    {
        IF_LOG Logger::print("ComplexExp::toConstElem(): %s @ %s\n", e->toChars(), e->type->toChars());
        LOG_SCOPE;
        result = DtoConstComplex(e->type, e->value.re, e->value.im);
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(StringExp *e)
    {
        IF_LOG Logger::print("StringExp::toConstElem: %s @ %s\n", e->toChars(), e->type->toChars());
        LOG_SCOPE;

        Type* t = e->type->toBasetype();
        Type* cty = t->nextOf()->toBasetype();

        bool nullterm = (t->ty != Tsarray);
        size_t endlen = nullterm ? e->len+1 : e->len;

        LLType* ct = voidToI8(DtoType(cty));
        LLArrayType* at = LLArrayType::get(ct,endlen);

#if LDC_LLVM_VER >= 305
        llvm::StringMap<llvm::GlobalVariable*>* stringLiteralCache = 0;
#else
        std::map<llvm::StringRef, llvm::GlobalVariable*>* stringLiteralCache = 0;
#endif
        LLConstant* _init;
        switch (cty->size())
        {
        default:
            llvm_unreachable("Unknown char type");
        case 1:
            _init = toConstantArray(ct, at, static_cast<uint8_t *>(e->string), e->len, nullterm);
            stringLiteralCache = &(gIR->stringLiteral1ByteCache);
            break;
        case 2:
            _init = toConstantArray(ct, at, static_cast<uint16_t *>(e->string), e->len, nullterm);
            stringLiteralCache = &(gIR->stringLiteral2ByteCache);
            break;
        case 4:
            _init = toConstantArray(ct, at, static_cast<uint32_t *>(e->string), e->len, nullterm);
            stringLiteralCache = &(gIR->stringLiteral4ByteCache);
            break;
        }

        if (t->ty == Tsarray)
        {
            result = _init;
            return;
        }

        llvm::StringRef key(e->toChars());
        llvm::GlobalVariable* gvar = (stringLiteralCache->find(key) ==
                                      stringLiteralCache->end())
                                     ? 0 : (*stringLiteralCache)[key];
        if (gvar == 0)
        {
            llvm::GlobalValue::LinkageTypes _linkage = llvm::GlobalValue::PrivateLinkage;
            gvar = new llvm::GlobalVariable(gIR->module, _init->getType(), true, _linkage, _init, ".str");
            gvar->setUnnamedAddr(true);
            (*stringLiteralCache)[key] = gvar;
        }

        llvm::ConstantInt* zero = LLConstantInt::get(LLType::getInt32Ty(gIR->context()), 0, false);
        LLConstant* idxs[2] = { zero, zero };
#if LDC_LLVM_VER >= 307
        LLConstant* arrptr = llvm::ConstantExpr::getGetElementPtr(isaPointer(gvar)->getElementType(), gvar, idxs, true);
#else
        LLConstant* arrptr = llvm::ConstantExpr::getGetElementPtr(gvar, idxs, true);
#endif

        if (t->ty == Tpointer)
        {
            result = arrptr;
        }
        else if (t->ty == Tarray)
        {
            LLConstant* clen = LLConstantInt::get(DtoSize_t(), e->len, false);
            result = DtoConstSlice(clen, arrptr, e->type);
        }
        else
        {
            llvm_unreachable("Unknown type for StringExp.");
        }
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(AddExp *e)
    {
        IF_LOG Logger::print("AddExp::toConstElem: %s @ %s\n", e->toChars(), e->type->toChars());
        LOG_SCOPE;

        // add to pointer
        Type* t1b = e->e1->type->toBasetype();
        if (t1b->ty == Tpointer && e->e2->type->isintegral())
        {
            llvm::Constant* ptr = toConstElem(e->e1);
            dinteger_t idx = undoStrideMul(e->loc, t1b, e->e2->toInteger());
#if LDC_LLVM_VER >= 307
            result = llvm::ConstantExpr::getGetElementPtr(isaPointer(ptr)->getElementType(), ptr, DtoConstSize_t(idx));
#else
            result = llvm::ConstantExpr::getGetElementPtr(ptr, DtoConstSize_t(idx));
#endif
        }
        else
        {
            e->error("expression '%s' is not a constant", e->toChars());
            if (!global.gag) fatal();
            result = llvm::UndefValue::get(DtoType(e->type));
        }
    }

    void visit(MinExp *e)
    {
        IF_LOG Logger::print("MinExp::toConstElem: %s @ %s\n", e->toChars(), e->type->toChars());
        LOG_SCOPE;

        Type* t1b = e->e1->type->toBasetype();
        if (t1b->ty == Tpointer && e->e2->type->isintegral())
        {
            llvm::Constant* ptr = toConstElem(e->e1);
            dinteger_t idx = undoStrideMul(e->loc, t1b, e->e2->toInteger());

            llvm::Constant* negIdx = llvm::ConstantExpr::getNeg(DtoConstSize_t(idx));
#if LDC_LLVM_VER >= 307
            result = llvm::ConstantExpr::getGetElementPtr(isaPointer(ptr)->getElementType(), ptr, negIdx);
#else
            result = llvm::ConstantExpr::getGetElementPtr(ptr, negIdx);
#endif
        }
        else
        {
            e->error("expression '%s' is not a constant", e->toChars());
            if (!global.gag) fatal();
            result = llvm::UndefValue::get(DtoType(e->type));
        }
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(CastExp *e)
    {
        IF_LOG Logger::print("CastExp::toConstElem: %s @ %s\n", e->toChars(), e->type->toChars());
        LOG_SCOPE;

        LLType* lltype = DtoType(e->type);
        Type* tb = e->to->toBasetype();

        // string literal to dyn array:
        // reinterpret the string data as an array, calculate the length
        if (e->e1->op == TOKstring && tb->ty == Tarray)
        {
#if 0
            StringExp *strexp = static_cast<StringExp*>(e1);
            size_t datalen = strexp->sz * strexp->len;
            Type* eltype = tb->nextOf()->toBasetype();
            if (datalen % eltype->size() != 0) {
                error("the sizes don't line up");
                return e1->toConstElem(p);
            }
            size_t arrlen = datalen / eltype->size();
#endif
            e->error("ct cast of string to dynamic array not fully implemented");
            result = toConstElem(e->e1);
        }
        // pointer to pointer
        else if (tb->ty == Tpointer && e->e1->type->toBasetype()->ty == Tpointer)
        {
            result = llvm::ConstantExpr::getBitCast(toConstElem(e->e1), lltype);
        }
        // global variable to pointer
        else if (tb->ty == Tpointer && e->e1->op == TOKvar)
        {
            VarDeclaration *vd = static_cast<VarExp*>(e->e1)->var->isVarDeclaration();
            assert(vd);
            DtoResolveVariable(vd);
            LLConstant *value = isIrGlobalCreated(vd) ? isaConstant(getIrGlobal(vd)->value) : 0;
            if (!value)
               goto Lerr;
            Type *type = vd->type->toBasetype();
            if (type->ty == Tarray || type->ty == Tdelegate) {
                LLConstant* idxs[2] = { DtoConstSize_t(0), DtoConstSize_t(1) };
#if LDC_LLVM_VER >= 307
                value = llvm::ConstantExpr::getGetElementPtr(isaPointer(value)->getElementType(), value, idxs, true);
#else
                value = llvm::ConstantExpr::getGetElementPtr(value, idxs, true);
#endif
            }
            result = DtoBitCast(value, DtoType(tb));
        }
        else if (tb->ty == Tclass && e->e1->type->ty == Tclass)
        {
            assert(e->e1->op == TOKclassreference);
            ClassDeclaration* cd = static_cast<ClassReferenceExp*>(e->e1)->originalClass();

            llvm::Constant* instance = toConstElem(e->e1);
            if (InterfaceDeclaration* it = static_cast<TypeClass*>(tb)->sym->isInterfaceDeclaration()) {
                assert(it->isBaseOf(cd, NULL));

                IrTypeClass* typeclass = cd->type->ctype->isClass();

                // find interface impl
                size_t i_index = typeclass->getInterfaceIndex(it);
                assert(i_index != ~0UL);

                // offset pointer
                instance = DtoGEPi(instance, 0, i_index);
            }
            result = DtoBitCast(instance, DtoType(tb));
        }
        else
        {
            goto Lerr;
        }
        return;

    Lerr:
        e->error("cannot cast %s to %s at compile time", e->e1->type->toChars(), e->type->toChars());
        if (!global.gag)
            fatal();
        result = llvm::UndefValue::get(DtoType(e->type));
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(SymOffExp *e)
    {
        IF_LOG Logger::println("SymOffExp::toConstElem: %s @ %s", e->toChars(), e->type->toChars());
        LOG_SCOPE;

        llvm::Constant* base = DtoConstSymbolAddress(e->loc, e->var);
        if (base == 0)
        {
            result = llvm::UndefValue::get(DtoType(e->type));
            return;
        }

        if (e->offset == 0)
        {
            result = base;
        }
        else
        {
            const unsigned elemSize = gDataLayout->getTypeStoreSize(
                base->getType()->getContainedType(0));

            IF_LOG Logger::println("adding offset: %llu (elem size: %u)", static_cast<unsigned long long>(e->offset), elemSize);

            if (e->offset % elemSize == 0)
            {
                // We can turn this into a "nice" GEP.
                result = llvm::ConstantExpr::getGetElementPtr(
#if LDC_LLVM_VER >= 307
                    LLType::getInt8Ty(gIR->context()),
#endif
                    base,
                    DtoConstSize_t(e->offset / elemSize));
            }
            else
            {
                // Offset isn't a multiple of base type size, just cast to i8* and
                // apply the byte offset.
                result = llvm::ConstantExpr::getGetElementPtr(
#if LDC_LLVM_VER >= 307
                    getVoidPtrType(),
#endif
                    DtoBitCast(base, getVoidPtrType()),
                    DtoConstSize_t(e->offset));
            }
        }

        result = DtoBitCast(result, DtoType(e->type));
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(AddrExp *e)
    {
        IF_LOG Logger::println("AddrExp::toConstElem: %s @ %s", e->toChars(), e->type->toChars());
        LOG_SCOPE;
        // FIXME: this should probably be generalized more so we don't
        // need to have a case for each thing we can take the address of

        // address of global variable
        if (e->e1->op == TOKvar)
        {
            VarExp* vexp = static_cast<VarExp*>(e->e1);
            LLConstant *c = DtoConstSymbolAddress(e->loc, vexp->var);
            result = c ? DtoBitCast(c, DtoType(e->type)) : 0;
        }
        // address of indexExp
        else if (e->e1->op == TOKindex)
        {
            IndexExp* iexp = static_cast<IndexExp*>(e->e1);

            // indexee must be global static array var
            assert(iexp->e1->op == TOKvar);
            VarExp* vexp = static_cast<VarExp*>(iexp->e1);
            VarDeclaration* vd = vexp->var->isVarDeclaration();
            assert(vd);
            assert(vd->type->toBasetype()->ty == Tsarray);
            DtoResolveVariable(vd);
            assert(isIrGlobalCreated(vd));

            // get index
            LLConstant* index = toConstElem(iexp->e2);
            assert(index->getType() == DtoSize_t());

            // gep
            LLConstant* idxs[2] = { DtoConstSize_t(0), index };
            LLConstant *val = isaConstant(getIrGlobal(vd)->value);
            val = DtoBitCast(val, DtoType(vd->type->pointerTo()));
#if LDC_LLVM_VER >= 307
            LLConstant* gep = llvm::ConstantExpr::getGetElementPtr(isaPointer(val)->getElementType(), val, idxs, true);
#else
            LLConstant* gep = llvm::ConstantExpr::getGetElementPtr(val, idxs, true);
#endif

            // bitcast to requested type
            assert(e->type->toBasetype()->ty == Tpointer);
            result = DtoBitCast(gep, DtoType(e->type));
        }
        else if (e->e1->op == TOKstructliteral)
        {
            StructLiteralExp* se = static_cast<StructLiteralExp*>(e->e1);

            if (se->globalVar)
            {
                IF_LOG Logger::cout() << "Returning existing global: " << *se->globalVar << '\n';
                result = se->globalVar;
                return;
            }

            se->globalVar = new llvm::GlobalVariable(p->module,
                DtoType(e->e1->type), false, llvm::GlobalValue::InternalLinkage, 0,
                ".structliteral");

            llvm::Constant* constValue = toConstElem(se);
            if (constValue->getType() != se->globalVar->getType()->getContainedType(0))
            {
                llvm::GlobalVariable* finalGlobalVar = new llvm::GlobalVariable(
                    p->module, constValue->getType(), false,
                    llvm::GlobalValue::InternalLinkage, 0, ".structliteral");
                se->globalVar->replaceAllUsesWith(
                    DtoBitCast(finalGlobalVar, se->globalVar->getType()));
                se->globalVar->eraseFromParent();
                se->globalVar = finalGlobalVar;
            }
            se->globalVar->setInitializer(constValue);
            se->globalVar->setAlignment(e->e1->type->alignsize());

            result = se->globalVar;
        }
        else if (e->e1->op == TOKslice)
        {
            e->error("non-constant expression '%s'", e->toChars());
            if (!global.gag) fatal();
            result = llvm::UndefValue::get(DtoType(e->type));
        }
        // not yet supported
        else
        {
            e->error("constant expression '%s' not yet implemented", e->toChars());
            fatal();
        }
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(FuncExp *e)
    {
        IF_LOG Logger::print("FuncExp::toConstElem: %s @ %s\n", e->toChars(), e->type->toChars());
        LOG_SCOPE;

        FuncLiteralDeclaration *fd = e->fd;
        assert(fd);

        if (fd->tok == TOKreserved && e->type->ty == Tpointer)
        {
            // This is a lambda that was inferred to be a function literal instead
            // of a delegate, so set tok here in order to get correct types/mangling.
            // Horrible hack, but DMD does the same thing in FuncExp::toElem and
            // other random places.
            fd->tok = TOKfunction;
            fd->vthis = NULL;
        }

        if (fd->tok != TOKfunction)
        {
            assert(fd->tok == TOKdelegate || fd->tok == TOKreserved);
            e->error("non-constant nested delegate literal expression %s", e->toChars());
            if (!global.gag) fatal();
            result = llvm::UndefValue::get(DtoType(e->type));
        }
        else
        {
            // We need to actually codegen the function here, as literals are not added
            // to the module member list.
            Declaration_codegen(fd, p);
            assert(getIrFunc(fd)->func);

            result = getIrFunc(fd)->func;
        }
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(ArrayLiteralExp *e)
    {
        IF_LOG Logger::print("ArrayLiteralExp::toConstElem: %s @ %s\n", e->toChars(), e->type->toChars());
        LOG_SCOPE;

        // extract D types
        Type* bt = e->type->toBasetype();
        Type* elemt = bt->nextOf();

        // build llvm array type
        LLArrayType* arrtype = LLArrayType::get(i1ToI8(voidToI8(DtoType(elemt))), e->elements->dim);

        // dynamic arrays can occur here as well ...
        bool dyn = (bt->ty != Tsarray);

        llvm::Constant* initval = arrayLiteralToConst(p, e);

        // if static array, we're done
        if (!dyn)
        {
            result = initval;
            return;
        }

        bool canBeConst = e->type->isConst() || e->type->isImmutable();
        llvm::GlobalVariable* gvar = new llvm::GlobalVariable(gIR->module,
            initval->getType(), canBeConst, llvm::GlobalValue::InternalLinkage, initval,
            ".dynarrayStorage");
        gvar->setUnnamedAddr(canBeConst);
        llvm::Constant* store = DtoBitCast(gvar, getPtrToType(arrtype));

        if (bt->ty == Tpointer)
        {
            // we need to return pointer to the static array.
            result = store;
            return;
        }

        // build a constant dynamic array reference with the .ptr field pointing into store
        LLConstant* idxs[2] = { DtoConstUint(0), DtoConstUint(0) };
#if LDC_LLVM_VER >= 307
        LLConstant* globalstorePtr = llvm::ConstantExpr::getGetElementPtr(isaPointer(store)->getElementType(), store, idxs, true);
#else
        LLConstant* globalstorePtr = llvm::ConstantExpr::getGetElementPtr(store, idxs, true);
#endif

        result = DtoConstSlice(DtoConstSize_t(e->elements->dim), globalstorePtr);
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(StructLiteralExp *e)
    {
        // type can legitimately be null for ClassReferenceExp::value.
        IF_LOG Logger::print("StructLiteralExp::toConstElem: %s @ %s\n",
            e->toChars(), e->type ? e->type->toChars() : "(null)");
        LOG_SCOPE;

        if (e->sinit)
        {
            // Copied from VarExp::toConstElem, need to clean this mess up.
            Type* sdecltype = e->sinit->type->toBasetype();
            IF_LOG Logger::print("Sym: type=%s\n", sdecltype->toChars());
            assert(sdecltype->ty == Tstruct);
            TypeStruct* ts = static_cast<TypeStruct*>(sdecltype);
            DtoResolveStruct(ts->sym);

            result = getIrAggr(ts->sym)->getDefaultInit();
        }
        else
        {
            // make sure the struct is resolved
            DtoResolveStruct(e->sd);

            std::map<VarDeclaration*, llvm::Constant*> varInits;
            const size_t nexprs = e->elements->dim;
            for (size_t i = 0; i < nexprs; i++)
            {
                if ((*e->elements)[i])
                {
                    varInits[e->sd->fields[i]] = toConstElem((*e->elements)[i]);
                }
            }

            result = getIrAggr(e->sd)->createInitializerConstant(varInits);
        }
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(ClassReferenceExp *e)
    {
        IF_LOG Logger::print("ClassReferenceExp::toConstElem: %s @ %s\n",
            e->toChars(), e->type->toChars());
        LOG_SCOPE;

        ClassDeclaration* origClass = e->originalClass();
        DtoResolveClass(origClass);
        StructLiteralExp *value = e->value;

        if (value->globalVar)
        {
            IF_LOG Logger::cout() << "Using existing global: " << *value->globalVar << '\n';
        }
        else
        {
            value->globalVar = new llvm::GlobalVariable(p->module,
                origClass->type->ctype->isClass()->getMemoryLLType(),
                false, llvm::GlobalValue::InternalLinkage, 0, ".classref");

            std::map<VarDeclaration*, llvm::Constant*> varInits;

            // Unfortunately, ClassReferenceExp::getFieldAt is badly broken – it
            // places the base class fields _after_ those of the subclass.
            {
                const size_t nexprs = value->elements->dim;

                std::stack<ClassDeclaration*> classHierachy;
                ClassDeclaration* cur = origClass;
                while (cur)
                {
                    classHierachy.push(cur);
                    cur = cur->baseClass;
                }
                size_t i = 0;
                while (!classHierachy.empty())
                {
                    cur = classHierachy.top();
                    classHierachy.pop();
                    for (size_t j = 0; j < cur->fields.dim; ++j)
                    {
                        if ((*value->elements)[i])
                        {
                            VarDeclaration* field = cur->fields[j];
                            IF_LOG Logger::println("Getting initializer for: %s", field->toChars());
                            LOG_SCOPE;
                            varInits[field] = toConstElem((*value->elements)[i]);
                        }
                        ++i;
                    }
                }
                assert(i == nexprs);
            }

            llvm::Constant* constValue = getIrAggr(origClass)->createInitializerConstant(varInits);

            if (constValue->getType() != value->globalVar->getType()->getContainedType(0))
            {
                llvm::GlobalVariable* finalGlobalVar = new llvm::GlobalVariable(
                    p->module, constValue->getType(), false,
                    llvm::GlobalValue::InternalLinkage, 0, ".classref");
                value->globalVar->replaceAllUsesWith(
                    DtoBitCast(finalGlobalVar, value->globalVar->getType()));
                value->globalVar->eraseFromParent();
                value->globalVar = finalGlobalVar;
            }
            value->globalVar->setInitializer(constValue);
        }

        result = value->globalVar;

        if (e->type->ty == Tclass) {
            ClassDeclaration* targetClass = static_cast<TypeClass*>(e->type)->sym;
            if (InterfaceDeclaration* it = targetClass->isInterfaceDeclaration()) {
                assert(it->isBaseOf(origClass, NULL));

                IrTypeClass* typeclass = origClass->type->ctype->isClass();

                // find interface impl
                size_t i_index = typeclass->getInterfaceIndex(it);
                assert(i_index != ~0UL);

                // offset pointer
                result = DtoGEPi(result, 0, i_index);
            }
        }

        assert(e->type->ty == Tclass || e->type->ty == Tenum);
        result = DtoBitCast(result, DtoType(e->type));
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(VectorExp *e)
    {
        IF_LOG Logger::print("VectorExp::toConstElem: %s @ %s\n", e->toChars(), e->type->toChars());
        LOG_SCOPE;

        TypeVector *tv = static_cast<TypeVector*>(e->to->toBasetype());
        assert(tv->ty == Tvector);

        // The AST for
        //   static immutable ubyte16 vec1 = 123;
        // differs from
        //    static immutable ubyte[16] vec1 = 123;
        // In the vector case the AST contains an IntegerExp (of type int) and a
        // CastExp to type ubyte. In the static array case the AST only contains an
        // IntegerExp of type ubyte. Simply call optimize to get  rid of the cast.
        // FIXME: Check DMD source to understand why two different ASTs are
        //        constructed.
        llvm::Constant *val = toConstElem(e->e1->optimize(WANTvalue));

        dinteger_t elemCount =
            static_cast<TypeSArray *>(tv->basetype)->dim->toInteger();
       result = llvm::ConstantVector::getSplat(elemCount, val);
    }

    //////////////////////////////////////////////////////////////////////////////////////////

    void visit(Expression *e)
    {
        e->error("expression '%s' is not a constant", e->toChars());
        if (!global.gag)
            fatal();

        // Do not return null here, as AssocArrayLiteralExp::toElem determines
        // whether it can allocate the needed arrays statically by just invoking
        // toConstElem on its key/value expressions, and handling the null value
        // consequently would require error-prone adaptions in all other code.
        result = llvm::UndefValue::get(DtoType(e->type));
    }
};

LLConstant *toConstElem(Expression *e, IRState *p)
{
    return ToConstElemVisitor(p).toConstElem(e);
}