HP aC++/HP C A.06.20 Programmer's Guide

Compiling files at optimization level 2 ("-O" or "+O2") and above increases the amount
of virtual memory needed by the compiler. In cases where very large functions or files
are compiled at +O2, or in cases where aggressive (+O3 and above) optimization is
used, ensure that the maxdsiz kernel tunable is set appropriately on the machine
where compilation takes place.
HP recommends a setting of 0x100000000, or 4 GB (the default for this parameter is
0x100000000, or 4 GB) for maxdsiz_64bit in such cases. Updating the
maxdsiz_64bit tunable will ensure that the compiler does not run out of virtual
memory when compiling large files or functions.
In addition, maxssiz_64bit should be set to 128 MB for very large or complex input
files. (Normally a maxssiz_64bit setting of 64 MB will be sufficient.)
See the kctune man page for more information on how to change kernel tunable
parameters.
-O
-O
The -O option invokes the optimizer to perform level 2 optimization. This option is
equivalent to +O2 option.
Example:
This command compiles prog.C and optimizes at level 2:
aCC -O prog.C
+O0
+O0
Use +O0 for fastest compile time or with simple programs. No optimizations are
performed.
Example:
This command compiles prog.C and optimizes at level 0:
aCC +O0 prog.C
+O1
+O1
The +O1 option performs level 1 optimization only. This includes branch optimization,
dead code elimination, faster register allocation, instruction scheduling, and peephole
optimization. This is the default optimization level.
Example:
This command compiles prog.C and optimizes at level 1:
aCC +O1 prog.C
Code Optimizing Options 67