src/tint/lang/wgsl/ast/transform/fold_constants.cc

// Copyright 2024 The Dawn & Tint Authors
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this
//    list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice,
//    this list of conditions and the following disclaimer in the documentation
//    and/or other materials provided with the distribution.
//
// 3. Neither the name of the copyright holder nor the names of its
//    contributors may be used to endorse or promote products derived from
//    this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include "src/tint/lang/wgsl/ast/transform/fold_constants.h"

#include <utility>

#include "src/tint/lang/core/constant/splat.h"
#include "src/tint/lang/core/fluent_types.h"
#include "src/tint/lang/core/type/abstract_float.h"
#include "src/tint/lang/core/type/abstract_int.h"
#include "src/tint/lang/core/type/bool.h"
#include "src/tint/lang/wgsl/program/clone_context.h"
#include "src/tint/lang/wgsl/program/program_builder.h"
#include "src/tint/lang/wgsl/resolver/resolve.h"
#include "src/tint/utils/rtti/switch.h"

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

TINT_INSTANTIATE_TYPEINFO(tint::ast::transform::FoldConstants);

namespace tint::ast::transform {
namespace {

struct State {
    enum class Splat {
        kAllowed,
        kDisallowed,
    };

    const ast::Expression* Constant(const core::constant::Value* c) {
        auto composite = [&](Splat splat) -> const ast::Expression* {
            auto ty = FoldConstants::CreateASTTypeFor(ctx, c->Type());
            if (c->AllZero()) {
                return b.Call(ty);
            }
            if (splat == Splat::kAllowed && c->Is<core::constant::Splat>()) {
                return b.Call(ty, Constant(c->Index(0)));
            }

            Vector<const ast::Expression*, 8> els;
            for (size_t i = 0, n = c->NumElements(); i < n; i++) {
                els.Push(Constant(c->Index(i)));
            }
            return b.Call(ty, std::move(els));
        };

        return tint::Switch(
            c->Type(),  //
            [&](const core::type::AbstractFloat*) { return b.Expr(c->ValueAs<AFloat>()); },
            [&](const core::type::AbstractInt*) { return b.Expr(c->ValueAs<AInt>()); },
            [&](const core::type::I32*) { return b.Expr(c->ValueAs<i32>()); },
            [&](const core::type::U32*) { return b.Expr(c->ValueAs<u32>()); },
            [&](const core::type::F32*) { return b.Expr(c->ValueAs<f32>()); },
            [&](const core::type::F16*) { return b.Expr(c->ValueAs<f16>()); },
            [&](const core::type::Bool*) { return b.Expr(c->ValueAs<bool>()); },
            [&](const core::type::Array*) { return composite(Splat::kDisallowed); },
            [&](const core::type::Vector*) { return composite(Splat::kAllowed); },
            [&](const core::type::Matrix*) { return composite(Splat::kDisallowed); },
            [&](const core::type::Struct*) { return composite(Splat::kDisallowed); },
            TINT_ICE_ON_NO_MATCH);
    }

    Transform::ApplyResult Run() {
        ctx.ReplaceAll([&](const Expression* expr) -> const Expression* {
            auto& sem = ctx.src->Sem();
            auto* ve = sem.Get<sem::ValueExpression>(expr);

            // No value expression SEM node found
            if (!ve) {
                return nullptr;
            }

            auto* cv = ve->ConstantValue();

            // No constant value for this expression
            if (!cv) {
                return nullptr;
            }

            if (cv->Type()->HoldsAbstract() && !cv->Type()->is_float_scalar() &&
                !cv->Type()->is_signed_integer_scalar() &&
                !cv->Type()->is_unsigned_integer_scalar()) {
                return nullptr;
            }

            return Constant(cv);
        });

        ctx.Clone();
        return resolver::Resolve(b);
    }

    const Program& src;
    ProgramBuilder b;
    program::CloneContext ctx{&b, &src, /* auto_clone_symbols */ true};
};

}  // namespace

FoldConstants::FoldConstants() = default;

FoldConstants::~FoldConstants() = default;

Transform::ApplyResult FoldConstants::Apply(const Program& src, const DataMap&, DataMap&) const {
    State s{src, {}};
    return s.Run();
}

}  // namespace tint::ast::transform