1 | .once
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2 |
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3 | .include "control-flow.dl"
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4 |
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5 | // Facts and Relations (Inputs)
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6 | // ============================
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7 |
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8 | // Statements can define and use variables.
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9 | .type Reference = Variable { v: symbol }
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10 | | Member { v: symbol, m: symbol }
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11 |
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12 | // Variable (or object) `r` is allocated, or assigned a literal value, in
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13 | // statement `s` of `f`.
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14 | .decl define(f:Function, s:Statement, r:Reference)
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15 | .input define
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16 |
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17 | // Variable (or object) `b` is assigned to another variable `a` in statement `s`
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18 | // of `f`.
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19 | .decl assign(f:Function, s:Statement, a:Reference, b:Reference)
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20 | .input assign
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21 |
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22 | // `a` (defined at statement `sf` in `f`) is aliased by `b` in statement `sg` in
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23 | // `g`.
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24 | .decl alias(f:Function, sf:Statement, a:Reference, g:Function, sg:Statement, b:Reference)
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25 | .output alias
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26 |
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27 | // Rules and Outputs
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28 | // =================
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29 |
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30 | // `r` is implicitly defined when it is assigned to.
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31 | define(f, s, r) :- assign(f, s, r, _).
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32 |
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33 | // Simple aliasing with locals.
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34 | // a = ...
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35 | // b = a
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36 | alias(f, s1, $Variable(v), f, s2, $Variable(v2)) :-
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37 | define(f, s1, $Variable(v)),
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38 | assign(f, s2, $Variable(v2), $Variable(v)),
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39 | CFGraph.reachable(f, s1, f, s2).
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40 |
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41 | // Objects can be aliased too. Note the special function name and statement
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42 | // number.
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43 | // a.b = ...
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44 | // c = a.b
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45 | alias("<heap>", -1, $Member(c, m), f, s2, r) :-
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46 | assign(_, _, $Member(c, m), _),
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47 | assign(f, s2, r, $Member(c, m)).
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48 |
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49 | // Object members can also be aliased by locals.
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50 | // a = ...
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51 | // b.c = a
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52 | alias(f, s1, $Variable(v), "<heap>", -1, $Member(c, m)) :-
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53 | define(f, s1, $Variable(v)),
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54 | assign(f, s2, $Member(c, m), $Variable(v)),
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55 | CFGraph.reachable(f, s1, f, s2).
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56 |
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57 | // Inductive case.
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58 | alias(f, s1, r, h, s2, r3) :-
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59 | alias(f, s1, r, g, _, r2),
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60 | alias(g, _, r2, h, s2, r3).
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