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

-qzerosize Option
Syntax
-qzerosize | -qnozerosize
ZEROSIZE | NOZEROSIZE
Improves performance of FORTRAN 77 and some Fortran 90 and Fortran 95
programs by preventing checking for zero-sized character strings and arrays.
For Fortran 90 and Fortran 95 programs that might process such objects, use
-qzerosize. For FORTRAN 77 programs, where zero-sized objects are not allowed,
or for Fortran 90 and Fortran 95 programs that do not use them, compiling with
-qnozerosize can improve the performance of some array or character-string
operations.
Defaults
The default setting depends on which command invokes the compiler: -qzerosize
for the xlf90, xlf90_r, xlf90_r7, xlf95, xlf95_r, xlf95_r7, f90, and f95 commands and
-qnozerosize for the xlf, xlf_r, xlf_r7, and f77/fort77 commands (for compatibility
with FORTRAN 77).
Rules
Run-time checking performed by the -C option takes slightly longer when
-qzerosize is in effect.
268 XL Fortran Enterprise Edition for AIX : User’s Guide