XL Fortran Enterprise Edition for AIX : User's Guide - IBM

v
-qcache=auto
Optimization level -O5 includes:
v Everything from -O4
v -qipa=level=2
If -O5 is specified on the compile step, then it should be specified on the link step,
as well. Although the -qipa option is not strictly another optimization level, it
extends the optimizations across procedures (even if the procedures are in different
files). It enhances the effectiveness of the optimizations that are done by other
optimization options, particularly -O (at any level) and -Q. Because it can also
increase compile time substantially, you may want to use it primarily for tuning
applications that are already debugged and ready to be used. If your application
contains a mixture of Fortran and C or C++ code compiled with IBM XL C/C+
compilers, you can achieve additional optimization by compiling and linking all
your code with the -O5 option.
Optimizing for a Target Machine or Class of Machines
Target machine options are options that instruct the compiler to generate code for
optimal execution on a given processor or architecture family. By default, the
compiler generates code that runs on all supported systems, but perhaps
suboptimally on a given system. By selecting appropriate target machine options,
you can optimize your application to suit the broadest possible selection of target
processors, a range of processors within a given family, or a specific processor. The
following compiler options control optimizations affecting individual aspects of the
target machine.
Target machine options
Option
Behavior
-q32 Generates code for a 32-bit addressing model (32-bit execution
mode).
-q64 Generates code for a 64-bit addressing model (64-bit execution
mode).
-qarch
-qtune
-qcache
Selects a family of processor architectures, or a specific architecture,
for which instruction code should be generated.
Biases optimization toward execution on a given processor, without
implying anything about the instruction set architecture to use as a
target.
Defines a specific cache or memory geometry. The defaults are set
through -qtune.
Selecting a predefined optimization level sets default values for these individual
options.
Related Information: See “-qarch Option” on page 127, “-qtune Option” on page
251, “-qcache Option” on page 137, and “Compiling for
Specific Architectures” on page 39.
Getting the Most out of Target Machine Options
Try to specify with -qarch the smallest family of machines possible that will be
expected to run your code reasonably well.
310 XL Fortran Enterprise Edition for AIX : User’s Guide