src/transform/fold_constants.cc

// Copyright 2021 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "src/transform/fold_constants.h"

#include <unordered_map>
#include <utility>
#include <vector>

#include "src/program_builder.h"
#include "src/sem/expression.h"

TINT_INSTANTIATE_TYPEINFO(tint::transform::FoldConstants);

namespace tint {
namespace transform {

FoldConstants::FoldConstants() = default;

FoldConstants::~FoldConstants() = default;

void FoldConstants::Run(CloneContext& ctx, const DataMap&, DataMap&) {
  ctx.ReplaceAll([&](ast::Expression* expr) -> ast::Expression* {
    auto* sem = ctx.src->Sem().Get(expr);
    if (!sem) {
      return nullptr;
    }

    auto value = sem->ConstantValue();
    if (!value.IsValid()) {
      return nullptr;
    }

    auto* ty = sem->Type();

    auto* ctor = expr->As<ast::TypeConstructorExpression>();
    if (!ctor) {
      return nullptr;
    }

    // If original ctor expression had no init values, don't replace the
    // expression
    if (ctor->values().size() == 0) {
      return nullptr;
    }

    if (auto* vec = ty->As<sem::Vector>()) {
      uint32_t vec_size = static_cast<uint32_t>(vec->Width());

      // We'd like to construct the new vector with the same number of
      // constructor args that the original node had, but after folding
      // constants, cases like the following are problematic:
      //
      // vec3<f32> = vec3<f32>(vec2<f32>, 1.0) // vec_size=3, ctor_size=2
      //
      // In this case, creating a vec3 with 2 args is invalid, so we should
      // create it with 3. So what we do is construct with vec_size args,
      // except if the original vector was single-value initialized, in
      // which case, we only construct with one arg again.
      uint32_t ctor_size = (ctor->values().size() == 1) ? 1 : vec_size;

      ast::ExpressionList ctors;
      for (uint32_t i = 0; i < ctor_size; ++i) {
        value.WithScalarAt(
            i, [&](auto&& s) { ctors.emplace_back(ctx.dst->Expr(s)); });
      }

      auto* el_ty = CreateASTTypeFor(ctx, vec->type());
      return ctx.dst->vec(el_ty, vec_size, ctors);
    }

    if (ty->is_scalar()) {
      return value.WithScalarAt(0, [&](auto&& s) { return ctx.dst->Expr(s); });
    }

    return nullptr;
  });

  ctx.Clone();
}

}  // namespace transform
}  // namespace tint