Function FoldRedundantSub

source/opt/const_folding_rules.cpp:994–1017

x - x = 0

// x - x = 0
ConstantFoldingRule FoldRedundantSub() {
  return [](IRContext* context, Instruction* inst,
            const std::vector<const analysis::Constant*>&)
             -> const analysis::Constant* {
    assert(inst->opcode() == spv::Op::OpFSub ||
           inst->opcode() == spv::Op::OpISub);

    if (inst->GetSingleWordInOperand(0) == inst->GetSingleWordInOperand(1)) {
      bool use_float = inst->opcode() == spv::Op::OpFSub;
      if (use_float && !inst->IsFloatingPointFoldingAllowed()) {
        return nullptr;
      }
      analysis::TypeManager* type_mgr = context->get_type_mgr();
      const analysis::Type* type = type_mgr->GetType(inst->type_id());
      if (type->IsCooperativeMatrix()) {
        return nullptr;
      }
      analysis::ConstantManager* const_mgr = context->get_constant_mgr();
      uint32_t null_id = const_mgr->GetNullConstId(type);
      return const_mgr->FindDeclaredConstant(null_id);
    }
    return nullptr;
  };
}

// Returns the constant that results from evaluating |numerator| / 0.0.  Returns
// |nullptr| if the result could not be evaluated.