copt - Online in the Cloud

PROGRAM:

NAME

copt - peephole optimizer

SYSNOPIS

copt file ...

DESCRIPTION

copt is a general-purpose peephole optimizer. It reads code from its standard input and
writes an improved version to its standard output. copy reads the named files for its
optimizations, which are encoded as follows:

<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>

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 %n 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

mov $%1,r%2
mov *r%2,r%2
=
mov %1,r%2

commands copt to replace runs like

mov $_a,r3
mov *r3,r3

with

mov _a,r3

Note that a tab or newline can terminate a %n variable.

copt 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 first instruction
of the replacement. copt matches input patterns in reverse order to cascade optimizations
without backing up.

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