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Document the -O0 and -O1 behaviors.

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Document the way the -O0 and -O1 options actually behave.  -O0, in
particular, is NASM 0.98 compatibility mode.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
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H. Peter Anvin 2008-09-30 16:24:47 -07:00
parent f1aefd8456
commit dc0bf47feb
2 changed files with 18 additions and 8 deletions
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@ -8,6 +8,12 @@ The NASM 2 series support x86-64, and is the production version of NASM
since 2007.
\S{cl-2.05} Version 2.05
\b Make the behaviour of \c{-O0} match NASM 0.98 legacy behavior.
See \k{opt-O}.
\S{cl-2.04} Version 2.04
\b Sanitize macro handing in the \c{%error} directive.

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doc/nasmdoc.src
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@ -787,22 +787,26 @@ NASM defaults to not optimizing operands which can fit into a signed byte.
This means that if you want the shortest possible object code,
you have to enable optimization.
Using the \c{-O} option, you can tell NASM to carry out different levels of optimization.
The syntax is:
Using the \c{-O} option, you can tell NASM to carry out different
levels of optimization. The syntax is:
\b \c{-O0}: No optimization. All operands take their long forms,
if a short form is not specified.
if a short form is not specified, except conditional jumps.
This is intended to match NASM 0.98 behavior.
\b \c{-O1}: Minimal optimization. As above, but immediate operands
which will fit in a signed byte are optimized,
unless the long form is specified.
unless the long form is specified. Conditional jumps default
to the long form unless otherwise specified.
\b \c{-Ox} (where \c{x} is the actual letter \c{x}): Multipass optimization.
Minimize branch offsets and signed immediate bytes,
overriding size specification unless the \c{strict} keyword
has been used (see \k{strict}). For compatability with earlier
releases, the letter \c{x} may also be any number greater than
one. This number has no effect on the actual number of passes.
overriding size specification unless the \c{strict} keyword
has been used (see \k{strict}). For compatability with earlier
releases, the letter \c{x} may also be any number greater than
one. This number has no effect on the actual number of passes.
The \c{-Ox} mode is recommended for most uses.
Note that this is a capital \c{O}, and is different from a small \c{o}, which
is used to specify the output file name. See \k{opt-o}.