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eda-tools/b2/genredmap.pl
Werner Almesberger 9cafe23fb8 b2/: simplified and corrected logic behind relop_redundant
We now generate the operator map algorithmically, which is a bit less
classy than solving the logical equations, but easier to get right.

Also renamed the somewhat vague "redundant" to "unreachable".
2012-06-01 14:52:12 -03:00

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#!/usr/bin/perl
#
# genredmap.pl - Redundacy detector map generator
#
# Copyright 2012 by Werner Almesberger
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
#
# This script finds the relational operators op = f(opa, opb), for which
# the following is true:
#
# forall A, B: (A op B) -> forall X: !(X opa A) -> !(X opa B)
#
# In other words: if, with X a variable and A and B constants, we have a
# cascade of the form
#
# if (X opa A) ...;
# else if (X opa B) ...;
#
# and A op B is true, then the second branch will never be taken.
#
%op = (
"lt" => sub { $_[0] < $_[1] },
"le" => sub { $_[0] <= $_[1] },
"eq" => sub { $_[0] == $_[1] },
"ge" => sub { $_[0] >= $_[1] },
"gt" => sub { $_[0] > $_[1] },
);
@ops = ("lt", "le", "eq", "ge", "gt");
$always = 0;
$a = 2;
@v = (0, 1, 2, 3, 4);
for $opa (@ops) {
#next unless $opa eq "lt";
for $opb (@ops) {
#next unless $opb eq "lt";
$best = 0;
OP: for $op (@ops) {
$hit = 0;
for $b (@v) {
#print "($opa, $opb) $a $op $b\n";
next unless $op{$op}->($a, $b);
for $x (@v) {
#print " A: $x $opa $a\n";
next if $op{$opa}->($x, $a);
#print " B: $x $opb $b\n";
next OP
if $op{$opb}->($x, $b) != $always;
$hit++;
#print " HIT ($hit)\n";
}
}
if ($hit > $best) {
$best = $hit;
$best_op = $op;
}
}
print "\t[idx_$opa][idx_$opb] = rel_$best_op,\n" if $best;
}
}