Sun Microsystems SunSoft Pascal 4.0, Руководство пользователя

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The Pascal Compiler 37
3
–O3
,
-xO3
Same as
-O2
, but optimizes the uses and definitions of external variables.
Level
-O3
does not trace the effects of pointer assignments. Do not use
Level
-O3
when compiling device drivers or programs that modify
external variables from within signal handlers.
–O4
,
-xO3
Same as
-O3
, but traces the effects of pointer assignments and gathers
alias information. Do not use Level
-O4
when compiling device drivers
or programs that modify external variables from within signal handlers.
-O5
,
-xO5
(Solaris 2.x only) Generates the highest level of optimization. This level
uses optimization algorithms that take more compilation time or that do
not have as high a certainty of improving execution time.
Optimization at this level is more likely to improve performance if it is
done with profile feedback. See
-xprofile
.
Note – Levels
-O3
and
-O4
may result in an increase in the size of the
executables. When optimizing for size, use level
-O2
. For most programs
,
–O4
is faster than
–O3
, which is faster than
–O2
, which is faster than
–O1
.
However, in a few cases
–O2
may be faster than the others, and
–O3
may be
faster than
–O4
. You can try compiling with each level to see if you have one
of these rare cases.
If the optimizer runs out of memory, it tries to recover by retrying the current
procedure at a lower level of optimization, then resumes subsequent
procedures at the original level specified in the
–O
command-line option.
If you optimize at
–O3
or
–O4
with very large procedures (thousands of lines of
code in a single procedure), the optimizer may require an unreasonable
amount of memory. Such cases may result in degraded machine performance.
You can prevent this from happening in the C shell by limiting the amount of
virtual memory available to a single process. To do this, use the limit
command (see
csh
(1)).
For example, to limit virtual memory to 16 megabytes:
hostname% limit datasize 16M