Compile-Time Operations

Visual Fortran does as many operations as possible at compile time rather than having them done at run time.

Constant Operations

Visual Fortran can perform many operations on constants (including PARAMETER constants):

• Constants preceded by a unary minus sign are negated.
• Expressions involving +, -, *, or / operators are evaluated; for example:

    PARAMETER (NN=27)
    I = 2*NN+J           ! Becomes: I = 54 + J
  

  Evaluation of some constant functions and operators is performed at compile time. This includes certain functions of constants, concatenation of string constants, and logical and relational operations involving constants.

• Lower-ranked constants are converted to the data type of the higher-ranked operand:

    REAL X, Y
    X = 10 * Y          ! Becomes: X = 10.0 * Y
  

• Array address calculations involving constant subscripts are simplified at compile time whenever possible:

    INTEGER I(10,10)
    I(1,2) = I(4,5)     ! Compiled as a direct load and store
  

Algebraic Reassociation Optimizations

Visual Fortran delays operations to see whether they have no effect or can be transformed to have no effect. If they have no effect, these operations are removed. A typical example involves unary minus and .NOT. operations:

  X = -Y * -Z           ! Becomes: Y * Z