HP Fortran Programmer's Guide (September 2007)

An overview of HP Fortran
Back-end
Chapter 110
Back-end
The two main functions of the back-end are:
• To optimize your program for faster performance
• To generate the code that goes into the object file
Optimization is performed by two subcomponents of the compiler’s back end:
• The High-Level Optimizer (HLO), which performs large-scale, high-semantic-level
analyses and transformations to increase performance.
• The low-level optimizer, which performs traditional optimizations (such as common
subexpression elimination and dead-code removal) as well as machine-specific
optimizations.
Options for controlling optimization form the largest group of the command-line options.
These options enable you to do the following:
• To set the level of optimization that is applied to your program
• To apply a package of optimizations that meet certain requirements of your
application—for example, optimizations that favor compile-time speed over performance
• To apply specific optimization technologies to your program, or to specific parts of your
program, for fine-tuning performance
Table 1-4 lists (in summary form) the options that control optimization. For information about
how to use these options, see “Using options to control optimization” on page 144.
NOTE If you use the f90 command to compile and link on separate command lines,
many of the optimization options must appear on both the command line and
the link line; see “Performance and optimization” on page 137. For information
about using f90 to compile and link, see “Linking with f90 vs. ld” on page 76.
Table 1-4 Options for controlling optimization
Option Function
+DC7200 Perform memory hierarchy optimizations for the PA7200
processor.