Function MergeMulNegateArithmetic

source/opt/folding_rules.cpp:892–929

Merges multiply of constant and negation. Cases: (-x) * 2 = x * -2 2 * (-x) = x * -2

// (-x) * 2 = x * -2
// 2 * (-x) = x * -2
FoldingRule MergeMulNegateArithmetic() {
  return [](IRContext* context, Instruction* inst,
            const std::vector<const analysis::Constant*>& constants) {
    assert(inst->opcode() == spv::Op::OpFMul ||
           inst->opcode() == spv::Op::OpIMul);
    analysis::ConstantManager* const_mgr = context->get_constant_mgr();
    const analysis::Type* type =
        context->get_type_mgr()->GetType(inst->type_id());

    if (type->IsCooperativeMatrix()) {
      return false;
    }

    bool uses_float = HasFloatingPoint(type);
    if (uses_float && !inst->IsFloatingPointFoldingAllowed()) return false;

    uint32_t width = ElementWidth(type);
    if (width != 32 && width != 64) return false;

    const analysis::Constant* const_input1 = ConstInput(constants);
    if (!const_input1) return false;
    Instruction* other_inst = NonConstInput(context, constants[0], inst);
    if (uses_float && !other_inst->IsFloatingPointFoldingAllowed())
      return false;

    if (other_inst->opcode() == spv::Op::OpFNegate ||
        other_inst->opcode() == spv::Op::OpSNegate) {
      uint32_t neg_id = NegateConstant(const_mgr, const_input1);

      inst->SetInOperands(
          {{SPV_OPERAND_TYPE_ID, {other_inst->GetSingleWordInOperand(0u)}},
           {SPV_OPERAND_TYPE_ID, {neg_id}}});
      return true;
    }

    return false;
  };
}

// Returns true if |inst| is negation op and is safe to fold.
static bool IsFoldableNegation(const Instruction* inst) {