LF Fortran Express User's Guide - Lahey Computer Systems, Inc.

Chapter 2 Developing with LF Fortran
Specify -ap to guarantee the consistency of REAL and COMPLEX calculations, regardless
of optimization level; user variables are not assigned to registers. Consider the following
example:
Example
X = S - T
2 Y = X - U
...
3 Y = X - U
By default (-nap), during compilation of statement 2, the compiler recognizes the value X is
already in a register and does not cause the value to be reloaded from memory. At statement
3, the value X may or may not already be in a register, and so the value may or may not be
reloaded accordingly. Because the precision of the datum is greater in a register than in memory,
a difference in precision at statements 2 and 3 may occur.
Specify -ap to choose the memory reference for non INTEGER operands; that is, registers
are reloaded. -ap must be specified when testing for the equality of randomly-generated
values.
The default, -nap, allows the compiler to take advantage of the current values in registers,
with possibly greater accuracy in low-order bits.
Specifying -ap will usually generate slower executables.
-BLOCK blocksize
Default blocksize
Compile only. Default: 8192 bytes
Default to a specific blocksize for file I/O (See the OPEN Statement in the LF Fortran Language
Reference). blocksize must be a decimal INTEGER constant. Specifying an optimal
blocksize can make an enormous improvement in the speed of your executable. The program
TRYBLOCK.F90 in the SRC directory demonstrates how changing blocksize can affect execution
speed. Some experimentation with blocksize in your program is usually necessary to
determine the optimal value.
-[N]C
Suppress Linking
Compile only. Default: -nc
Specify -c to create object (.OBJ), and, if necessary, module (.MOD) files without creating
an executable. This is especially useful in make files, where it is not always desirable to perform
the entire build process with one invocation of the driver.
-[N]CHK [([a][,e][,s][,u][,x])]
Checking
Compile only. Default: -nchk
30 LF Fortran Express User’s Guide