Constant-fold isValid calls when possible

[mihaibudiu]

Signed-off-by: Mihai Budiu mbudiu@vmware.com
Fixes #3779

[rst0git]

The "else if" conditions are unnecessary because return would prevent the execution of subsequent statements. Perhaps we can simplify this method to something like:

const IR::Node* DoConstantFolding::postorder(IR::Member* e) {
    if (!typesKnown) return e;
    auto orig = getOriginal<IR::Member>();
    auto type = typeMap->getType(orig->expr, true);
    auto origtype = typeMap->getType(orig);

    if (type->is<IR::Type_Stack>() && e->member == IR::Type_Stack::arraySize) {
        auto st = type->to<IR::Type_Stack>();
        auto size = st->getSize();
        return new IR::Constant(st->size->srcInfo, origtype, size);
    }

    auto expr = getConstant(e->expr);
    if (expr == nullptr) return e;

    auto structType = type->to<IR::Type_StructLike>();
    if (structType == nullptr) BUG("Expected a struct type, got %1%", type);

    if (auto list = expr->to<IR::ListExpression>()) {
        bool found = false;
        int index = 0;
        for (auto f : structType->fields) {
            if (f->name.name == e->member.name) {
                found = true;
                break;
            }
            index++;
        }

        if (!found) BUG("Could not find field %1% in type %2%", e->member, type);
        return CloneConstants::clone(list->components.at(index), this);
    }

    if (auto si = expr->to<IR::StructExpression>()) {
        if (type->is<IR::Type_Header>() && e->member.name == IR::Type_Header::isValid) return e;
        auto ne = si->components.getDeclaration<IR::NamedExpression>(e->member.name);
        BUG_CHECK(ne != nullptr, "Could not find field %1% in initializer %2%", e->member, si);
        return CloneConstants::clone(ne->expression, this);
    }

    if (expr->is<IR::InvalidHeader>() && e->member.name == IR::Type_Header::isValid) {
        return e;
    }

    BUG("Unexpected initializer: %1%", expr);
}

[jafingerhut]

LGTM. As usual I am only reviewing the test program and its expected outputs, not the code changes within p4c.

[mihaibudiu]

Thank you @rst0git, I will leave such improvements for a future PR.