During compilation, a compiler gathers information about the use of
variables and passes it to the Optimizer.
The MPE/iX Optimizer uses the information to ensure
that each code transformation it performs maintains
the correctness of the program (at least to the extent
that the original unoptimized program is correct).
The compiler assumes that inside a subroutine or function, only
the following variables can be accessed directly,
indirectly, or by another function call:
Common variables declared in this routine.
Local variables (static and dynamic).
Parameters to this routine.
Global variables visible in this routine.
If you have code that violates these assumptions, Optimizer can change
the behavior of the program in an undesirable way.
Avoid the following coding practices to ensure correct program execution
in optimized code:
Referencing outside the described bounds of an array.
This can cause address corruption or cause the program to
abort when it is run.
Using variables that can be accessed by a process other than
the program, such as shared common variables.
The compiler assumes that the program is the only process
accessing the data. (HP FORTRAN 77/iX has some exceptions.)
HP C/iX, HP Pascal/iX, and HP FORTRAN 77/iX provide compiler options to
change the assumptions about a routine.
Avoid using variables before they have been initialized.
The optimized version of a program may run differently than the
unoptimized version.
For detailed information, refer to
HP FORTRAN 77/iX Programmer's Guide Supplement
(31501-90002)
and HP Pascal/iX Programmer's Guide (31502-90002).
