# GAP Message (Diagnostic ID 30531)

## Message

Store the value of the upper-bound expression of the loop at line %d into a temporary local variable, and use this variable as the new upper-bound expression of the loop. To do this, insert a statement of the form "temp = upper-bound of loop" right before the loop, where "temp" is the newly created local variable. Choose a variable name that is unique, then replace the loop's original upper-bound expression with "temp".

## Advice

Use a local-variable for the loop upper-bound if the upper-bound does not change during the execution of the loop. This enables the compiler to recognize the loop as a proper counted do loop, which enables various loop optimizations including vectorization and parallelization.

This message appears when the compiler cannot output the exact upper-bound variable to be replaced.

## Example

Consider the following:

    class FooClass  {
    public:
        const int getValue() { return m_numTimeSteps;}
            void Foo2(double*  vec);
    private:
            int m_numTimeSteps;
    };
    void FooClass::Foo2(double*  vec)
    {
            // this will not vectorize
            for (int k=0; k < m_numTimeSteps; k++)
                    vec[k] = 0.0;

            // this will not vectorize
            for (int k=0; k < getValue(); k++)
                    vec[k] = 0.0;

            // this will vectorize
            int ub1 = m_numTimeSteps;
            for (int k=0; k < ub1; k++)
                    vec[k] = 0.0;

            // this will vectorize
            int ub2 = getValue();
            for (int k=0; k < ub2; k++)
                    vec[k] = 0.0;
    }

Parent topic: Guided Auto Parallelism Messages

## Verify

Confirm that the value of the upper-bound expression does not change throughout the entire execution of the loop.

## See Also

GAP Message (Diagnostic ID 30532)