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

equivalence (a, b(3))
t = b; a = t
t = a(10:1:-1); a = t
end subroutine
When SUB1 is called, an alias exists between J and K. J and K refer to the same
item in storage.
CALL SUB1(I,I)
...
SUBROUTINE SUB1(J,K)
In the following example, the program might store 5 instead of 6 into J unless
-qalias=nostd indicates that an alias might exist.
INTEGER BIG(1000)
INTEGER SMALL(10)
COMMON // BIG
EQUIVALENCE(BIG,SMALL)
...
BIG(500) = 5
SMALL (I) = 6 ! Where I has the value 500
J = BIG(500)
Restrictions
Because this option inhibits some optimizations of some variables, using it can
lower performance.
Programs that contain nonstandard or integer POINTER aliasing may produce
incorrect results if you do not compile them with the correct -qalias settings. The
xlf90, xlf90_r, xlf90_r7, xlf95, xlf95_r, xlf95_r7, f90, and f95 commands assume that
a program contains only standard aliasing (-qalias=aryovrlp:pteovrlp:std:nointptr),
while the xlf_r, xlf_r7, xlf, and f77/fort77 commands, for compatibility with XL
Fortran Version 2, assume that integer POINTERs may be present
(-qalias=aryovrlp:pteovrlp:std:intptr).
124 XL Fortran Enterprise Edition for AIX : User’s Guide