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#include "src/tint/lang/core/ir/transform/dead_code_elimination.h"

#include <vector>

#include "src/tint/lang/core/ir/builder.h"
#include "src/tint/lang/core/ir/module.h"
#include "src/tint/lang/core/ir/validator.h"
#include "src/tint/utils/ice/ice.h"

using namespace tint::core::fluent_types;     // NOLINT
using namespace tint::core::number_suffixes;  // NOLINT

namespace tint::core::ir::transform {

namespace {

/// PIMPL state for the transform.
struct State {
    /// The IR module.
    Module& ir_;

    /// The IR builder.
    Builder b_{ir_};

    /// Process the module.
    void Process() {
        auto funcs = ir_.DependencyOrderedFunctions();
        for (auto iter = funcs.rbegin(); iter != funcs.rend(); ++iter) {
            auto func = *iter;
            if (func->IsEntryPoint()) {
                continue;
            }

            bool used = false;
            for (auto usage : func->UsagesUnsorted()) {
                if (usage->instruction->Is<core::ir::Call>()) {
                    used = true;
                    break;
                }
            }

            if (!used) {
                ir_.Destroy(func);
            }
        }

        // Find any unused vars, do this after removing functions in case the usage was in a
        // function which is unused.
        auto* next = ir_.root_block->Front();
        while (next) {
            auto* inst = next;
            next = inst->next;

            if (inst->Result()->IsUsed()) {
                continue;
            }

            // Only want to process `var`s
            auto* var = inst->As<core::ir::Var>();
            if (!var) {
                continue;
            }

            auto* ptr = var->Result()->Type()->As<core::type::Pointer>();
            TINT_IR_ASSERT(ir_, ptr);

            auto space = ptr->AddressSpace();
            if (space != core::AddressSpace::kOut && space != core::AddressSpace::kIn &&
                space != core::AddressSpace::kPrivate) {
                continue;
            }

            inst->Destroy();
        }
    }
};

}  // namespace

Result<SuccessType> DeadCodeElimination(Module& ir) {
    core::ir::AssertValid(ir, kDeadCodeEliminationCapabilities, "before core.DeadCodeElimination");

    State{ir}.Process();

    return Success;
}

}  // namespace tint::core::ir::transform
