Sun Microsystems SunSoft Pascal 4.0, User Manual

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36 Pascal 4.0 User’s Guide
3
-notrace
The
-notrace
option disables runtime traceback. It is only effective when
compiling the main program.
–O[
level
]
The
–O
option instructs the compiler to run the compiled program through the
object code optimizer. The
–O
option also calls the
–P
option, which ensures
boolean
expressions are only evaluated as much as needed to determine the
result. This process causes an increase in compile time in exchange for a
decrease in compiled code size and execution time.
There are four levels of optimization. You indicate the level by specifying a
digit from 1 to 4 after the
–O
option. If you leave out the digit, the
optimization level defaults to
–O2
.
The level numbers are interpreted as follows:
–O
This is the most likely level of optimization to give fastest performance
for most reasonable applications. The default is
–O2
.
–O1,-xO1
This is the minimum amount of optimization (peephole) and is postpass
assembly-level. Do not use
–O1
unless
-O2
and
-O3
result in excessive
compilation time or shortage of swap space.
–O2
,
-xO2
This is the basic local and global optimization—induction-variable
elimination, local and global common subexpression elimination,
algebraic simplification, copy propagation, constant propagation, loop-
invariant optimization, register allocation, control-flow optimization,
tail-recursion elimination, dead-code elimination, and tail-call
elimination.
Level
-O2
does not optimize references to or definitions of external or
indirect variables. This level is the appropriate level for device drivers
and programs that modify external variables from within signal
handlers.