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

-qalias Option
Syntax
-qalias={[no]aryovrlp | [no]intptr | [no]pteovrlp | [no]std}...
ALIAS( {[NO]ARYOVRLP | [NO]INTPTR | [NO]PTEOVRLP | [NO]STD}... )
Indicates whether a program contains certain categories of aliasing. The compiler
limits the scope of some optimizations when there is a possibility that different
names are aliases for the same storage locations. See “Optimizing XL Fortran
Programs” on page 305 for information on aliasing strategies you should consider.
Arguments
aryovrlp | noaryovrlp
Indicates whether the compilation units contain any array assignments
between storage-associated arrays. If not, specify noaryovrlp to improve
performance.
intptr | nointptr
Indicates whether the compilation units contain any integer POINTER
statements. If so, specify INTPTR.
pteovrlp | nopteovrlp
Indicates whether any pointee variables may be used to refer to any data
objects that are not pointee variables, or whether two pointee variables
may be used to refer to the same storage location. If not, specify
NOPTEOVRLP.
std | nostd
Indicates whether the compilation units contain any nonstandard aliasing
(which is explained below). If so, specify nostd.
Rules
An alias exists when an item in storage can be referred to by more than one name.
The Fortran 90 and Fortran 95 standards allow some types of aliasing and disallow
some others. The sophisticated optimizations that the XL Fortran compiler
performs increase the likelihood of undesirable results when nonstandard aliasing
is present, as in the following situations:
v
v
v
v
The same data object is passed as an actual argument two or more times in the
same subprogram reference. The aliasing is not valid if either of the actual
arguments becomes defined, undefined, or redefined.
A subprogram reference associates a dummy argument with an object that is
accessible inside the referenced subprogram. The aliasing is not valid if any part
of the object associated with the dummy argument becomes defined, undefined,
or redefined other than through a reference to the dummy argument.
A dummy argument becomes defined, undefined, or redefined inside a called
subprogram, and where the dummy argument was not passed as an actual
argument to that subprogram.
Subscripting beyond the bounds of an array within a common block.
Applicable Product Levels
-qalias=nostd replaces the option -qxflag=xalias and makes it obsolete.
The introduction of the -qipa option does not remove the need for -qalias.
122 XL Fortran Enterprise Edition for AIX : User’s Guide