Function FoldExtractWithConstants

source/opt/const_folding_rules.cpp:110–138

Folds an OpcompositeExtract where input is a composite constant.

// Folds an OpcompositeExtract where input is a composite constant.
ConstantFoldingRule FoldExtractWithConstants() {
  return [](IRContext* context, Instruction* inst,
            const std::vector<const analysis::Constant*>& constants)
             -> const analysis::Constant* {
    const analysis::Constant* c = constants[kExtractCompositeIdInIdx];
    if (c == nullptr) {
      return nullptr;
    }

    for (uint32_t i = 1; i < inst->NumInOperands(); ++i) {
      uint32_t element_index = inst->GetSingleWordInOperand(i);
      if (c->AsNullConstant()) {
        // Return Null for the return type.
        analysis::ConstantManager* const_mgr = context->get_constant_mgr();
        analysis::TypeManager* type_mgr = context->get_type_mgr();
        return const_mgr->GetConstant(type_mgr->GetType(inst->type_id()), {});
      }

      auto cc = c->AsCompositeConstant();
      assert(cc != nullptr);
      auto components = cc->GetComponents();
      // Protect against invalid IR.  Refuse to fold if the index is out
      // of bounds.
      if (element_index >= components.size()) return nullptr;
      c = components[element_index];
    }
    return c;
  };
}

// Folds an OpcompositeInsert where input is a composite constant.
ConstantFoldingRule FoldInsertWithConstants() {