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#include "src/tint/lang/spirv/writer/raise/remove_unreachable_in_loop_continuing.h"

#include <utility>

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

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

namespace tint::spirv::writer::raise {

namespace {

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

    /// The IR builder.
    core::ir::Builder b{ir};

    /// Process the module.
    void Process() {
        // Find all unreachable instructions.
        for (auto* inst : ir.Instructions()) {
            if (auto* unreachable = inst->As<core::ir::Unreachable>()) {
                Process(unreachable);
            }
        }
    }

    /// Check and replace an unreachable instruction if necessary.
    /// @param unreachable the instruction to check and maybe replace
    void Process(core::ir::Unreachable* unreachable) {
        // Walk up the control stack to see if we are inside a loop continuing block.
        auto* block = unreachable->Block();
        while (block->Parent()) {
            auto* control = block->Parent();
            if (auto* loop = control->As<core::ir::Loop>()) {
                if (loop->Continuing() == block) {
                    Replace(unreachable);
                    return;
                }
            }
            block = control->Block();
        }
    }

    /// Replace an unreachable instruction.
    /// @param unreachable the instruction to replace
    void Replace(core::ir::Unreachable* unreachable) {
        auto* control = unreachable->Block()->Parent();

        // Fill the exit argument with `undef`.
        Vector<core::ir::Value*, 4> exit_args;
        exit_args.Resize(control->Results().Length());

        // Replace the `unreachable` with an instruction that exits from the control construct.
        auto* exit = b.Exit(unreachable->Block()->Parent(), std::move(exit_args));
        unreachable->ReplaceWith(exit);
        unreachable->Destroy();
    }
};

}  // namespace

Result<SuccessType> RemoveUnreachableInLoopContinuing(core::ir::Module& ir) {
    core::ir::AssertValid(ir, kRemoveUnreachableInLoopContinuingCapabilities,
                          "before spirv.RemoveUnreachableInLoopContinuing");

    State{ir}.Process();

    return Success;
}

}  // namespace tint::spirv::writer::raise
