src/tint/lang/msl/writer/raise/switch_return.cc

// Copyright 2026 The Dawn & Tint Authors
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#include "src/tint/lang/msl/writer/raise/switch_return.h"

#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/lang/core/type/u32.h"
#include "src/tint/lang/msl/ir/builtin_call.h"

namespace tint::msl::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};

    /// The type manager.
    core::type::Manager& ty{ir.Types()};

    /// Process the module.
    void Process() {
        // Find all return instructions inside switches.
        Vector<core::ir::Return*, 8> returns_to_wrap;

        for (auto* fn : ir.functions) {
            fn->ForEachUseSorted([&](const core::ir::Usage& usage) {
                if (auto* ret = usage.instruction->As<core::ir::Return>()) {
                    auto* parent = ret->Block()->Parent();
                    if (parent && parent->Is<core::ir::Switch>()) {
                        returns_to_wrap.Push(ret);
                    }
                }
            });
        }

        // Wrap return in volatile zero conditional to work around a driver bug
        // (crbug.com/508638064).
        for (auto* ret : returns_to_wrap) {
            b.InsertBefore(ret, [&] {
                auto* zero = b.Call<msl::ir::BuiltinCall>(ty.u32(), msl::BuiltinFn::kVolatileZero);
                auto* cond = b.If(b.Equal(zero, b.Constant(core::u32(0))));
                b.Append(cond->True(), [&] {
                    if (ret->Value()) {
                        b.Return(ret->Func(), ret->Value());
                    } else {
                        b.Return(ret->Func());
                    }
                });
                b.Exit(ret->Block()->Parent());
            });
            ret->Destroy();
        }
    }
};

}  // namespace

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

    State{ir}.Process();

    return Success;
}

}  // namespace tint::msl::writer::raise