.de DS
.nf
.in +3
.sp
..
.de DE
.sp
.in -3
.fi
..
.TH copt 1
.SH NAME
copt \- peephole optimizer
.SH SYNOPSIS
\fBcopt\fP \fIfile\fP ...
.SH DESCRIPTION
\fIcopt\fP is a general-purpose peephole optimizer.
It reads code from its standard input
and writes an improved version to its standard output.
\fIcopt\fP reads the named files for its optimizations,
which are encoded as follows:
.DS
<pattern for input line 1>
<pattern for input line 2>
 ...
<pattern for input line n>
=
<pattern for output line 1>
<pattern for output line 2>
 ...
<pattern for output line m>
<blank line>
.DE
Pattern matching uses literal string comparison, with one exception:
``%%'' matches the ``%'' character,
and ``%'' followed by a digit matches everything
up to the next occurrence of the next pattern character,
though all occurrences of %\fIn\fP must denote the same string.
For example, the pattern ``%1=%1.'' matches exactly those strings
that begin with a string X, followed by a ``='' (the first),
followed by a second occurrence of X, followed by a period.
In this way, the input/output pattern
.DS
mov $%1,r%2
mov *r%2,r%2
=
mov %1,r%2
.DE
commands \fIcopt\fP to replace runs like
.DS
mov $_a,r3
mov *r3,r3
.DE
with
.DS
mov _a,r3
.DE
Note that a tab or newline can terminate a %\fIn\fP variable.
.LP
\fIcopt\fP compares each run of input patterns 
with the current input instruction and its predecessors.
If no match is found, it advances to the next input instruction and tries again.
Otherwise, it replaces the input instructions
with the corresponding output patterns, pattern variables instantiated,
and resumes its search with the \fIfirst\fP instruction of the replacement.
\fIcopt\fP matches input patterns in reverse order 
to cascade optimizations without backing up.
.SH BUGS
Errors in optimization files are always possible.