## lustrec / src / liveness.ml @ b4d9710b

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1 | a2d97a3e | ploc | (********************************************************************) |
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2 | (* *) |
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3 | (* The LustreC compiler toolset / The LustreC Development Team *) |
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4 | (* Copyright 2012 - -- ONERA - CNRS - INPT *) |
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5 | (* *) |
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6 | (* LustreC is free software, distributed WITHOUT ANY WARRANTY *) |
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7 | (* under the terms of the GNU Lesser General Public License *) |
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8 | (* version 2.1. *) |
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9 | (* *) |
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10 | (********************************************************************) |
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11 | 695d6f2f | xthirioux | |

12 | open Utils |
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13 | open LustreSpec |
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14 | open Corelang |
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15 | 3bfed7f9 | xthirioux | open Graph |

16 | 695d6f2f | xthirioux | open Causality |

17 | |||

18 | b13a7d5f | xthirioux | type context = |

19 | { |
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20 | mutable evaluated : Disjunction.CISet.t; |
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21 | dep_graph : IdentDepGraph.t; |
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22 | disjoint : (ident, Disjunction.CISet.t) Hashtbl.t; |
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23 | policy : (ident, var_decl) Hashtbl.t; |
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24 | } |
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25 | |||

26 | 8a183477 | xthirioux | (* computes the in-degree for each local variable of node [n], according to dep graph [g]. |

27 | *) |
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28 | let compute_fanin n g = |
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29 | let locals = ISet.diff (ExprDep.node_local_variables n) (ExprDep.node_memory_variables n) in |
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30 | let fanin = Hashtbl.create 23 in |
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31 | begin |
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32 | IdentDepGraph.iter_vertex (fun v -> if ISet.mem v locals then Hashtbl.add fanin v (IdentDepGraph.in_degree g v)) g; |
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33 | fanin |
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34 | end |
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35 | |||

36 | let pp_fanin fmt fanin = |
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37 | begin |
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38 | Format.fprintf fmt "{ /* locals fanin: */@."; |
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39 | Hashtbl.iter (fun s t -> Format.fprintf fmt "%s -> %d@." s t) fanin; |
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40 | Format.fprintf fmt "}@." |
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41 | end |
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42 | 3bfed7f9 | xthirioux | |

43 | (* computes the cone of influence of a given [var] wrt a dependency graph [g]. |
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44 | *) |
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45 | let cone_of_influence g var = |
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46 | (*Format.printf "coi: %s@." var;*) |
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47 | let frontier = ref (ISet.add var ISet.empty) in |
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48 | let coi = ref ISet.empty in |
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49 | while not (ISet.is_empty !frontier) |
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50 | do |
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51 | let head = ISet.min_elt !frontier in |
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52 | (*Format.printf "head: %s@." head;*) |
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53 | frontier := ISet.remove head !frontier; |
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54 | if ExprDep.is_read_var head then coi := ISet.add (ExprDep.undo_read_var head) !coi; |
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55 | List.iter (fun s -> frontier := ISet.add s !frontier) (IdentDepGraph.succ g head); |
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56 | done; |
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57 | !coi |
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58 | |||

59 | b6a94a4e | xthirioux | let compute_unused_variables n g = |

60 | 3bfed7f9 | xthirioux | let inputs = ExprDep.node_input_variables n in |

61 | let mems = ExprDep.node_memory_variables n in |
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62 | let outputs = ExprDep.node_output_variables n in |
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63 | ISet.fold |
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64 | (fun var unused -> ISet.diff unused (cone_of_influence g var)) |
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65 | (ISet.union outputs mems) |
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66 | a38c681e | xthirioux | (ISet.union inputs mems) |

67 | 3bfed7f9 | xthirioux | |

68 | b6a94a4e | xthirioux | (* computes the set of potentially reusable variables. |

69 | We don't reuse input variables, due to possible aliasing *) |
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70 | let node_reusable_variables node = |
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71 | let mems = ExprDep.node_memory_variables node in |
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72 | List.fold_left |
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73 | (fun acc l -> |
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74 | if ISet.mem l.var_id mems then acc else Disjunction.CISet.add l acc) |
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75 | Disjunction.CISet.empty |
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76 | node.node_locals |
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77 | |||

78 | b13a7d5f | xthirioux | let kill_root ctx head = |

79 | IdentDepGraph.iter_succ (IdentDepGraph.remove_edge ctx.dep_graph head.var_id) ctx.dep_graph head.var_id |
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80 | |||

81 | b6a94a4e | xthirioux | (* Recursively removes useless variables, |

82 | b13a7d5f | xthirioux | i.e. [ctx.evaluated] variables that are current roots of the dep graph [ctx.dep_graph] |

83 | 45c13277 | xthirioux | - [evaluated] is the set of already evaluated variables, |

84 | wrt the scheduling |
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85 | b13a7d5f | xthirioux | - does only remove edges, not variables themselves |

86 | 45c13277 | xthirioux | *) |

87 | b13a7d5f | xthirioux | let remove_roots ctx = |

88 | 695d6f2f | xthirioux | let rem = ref true in |

89 | b13a7d5f | xthirioux | let remaining = ref ctx.evaluated in |

90 | 695d6f2f | xthirioux | while !rem |

91 | do |
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92 | rem := false; |
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93 | b13a7d5f | xthirioux | let all_roots = graph_roots ctx.dep_graph in |

94 | let frontier_roots = Disjunction.CISet.filter (fun v -> List.mem v.var_id all_roots) !remaining in |
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95 | if not (Disjunction.CISet.is_empty frontier_roots) then |
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96 | 695d6f2f | xthirioux | begin |

97 | rem := true; |
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98 | b13a7d5f | xthirioux | Disjunction.CISet.iter (kill_root ctx) frontier_roots; |

99 | remaining := Disjunction.CISet.diff !remaining frontier_roots |
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100 | 695d6f2f | xthirioux | end |

101 | b13a7d5f | xthirioux | done |

102 | a38c681e | xthirioux | |

103 | ed81df06 | xthirioux | (* checks whether a variable is aliasable, |

104 | depending on its (address) type *) |
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105 | let is_aliasable var = |
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106 | Types.is_address_type var.var_type |
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107 | |||

108 | b6a94a4e | xthirioux | (* checks whether a variable [v] is an input of the [var] equation, with an address type. |

109 | if so, [var] could not safely reuse/alias [v], should [v] be dead in the caller node, |
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110 | because [v] may not be dead in the callee node when [var] is assigned *) |
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111 | let is_aliasable_input node var = |
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112 | let eq_var = get_node_eq var node in |
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113 | let inputs_var = |
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114 | match NodeDep.get_callee eq_var.eq_rhs with |
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115 | | None -> [] |
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116 | | Some (_, args) -> List.fold_right (fun e r -> match e.expr_desc with Expr_ident id -> id::r | _ -> r) args [] in |
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117 | 45c13277 | xthirioux | fun v -> is_aliasable v && List.mem v.var_id inputs_var |

118 | b6a94a4e | xthirioux | |

119 | 45c13277 | xthirioux | (* replace variable [v] by [v'] in graph [g]. |

120 | [v'] is a dead variable |
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121 | 695d6f2f | xthirioux | *) |

122 | 45c13277 | xthirioux | let replace_in_dep_graph v v' g = |

123 | 695d6f2f | xthirioux | begin |

124 | b6a94a4e | xthirioux | IdentDepGraph.add_vertex g v'; |

125 | IdentDepGraph.iter_succ (fun s -> IdentDepGraph.add_edge g v' s) g v; |
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126 | IdentDepGraph.iter_pred (fun p -> IdentDepGraph.add_edge g p v') g v; |
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127 | IdentDepGraph.remove_vertex g v |
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128 | 695d6f2f | xthirioux | end |

129 | |||

130 | 45c13277 | xthirioux | let pp_reuse_policy fmt policy = |

131 | begin |
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132 | Format.fprintf fmt "{ /* reuse policy */@."; |
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133 | Hashtbl.iter (fun s t -> Format.fprintf fmt "%s -> %s@." s t.var_id) policy; |
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134 | Format.fprintf fmt "}@." |
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135 | end |
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136 | |||

137 | let pp_context fmt ctx = |
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138 | begin |
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139 | Format.fprintf fmt "{ /*BEGIN context */@."; |
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140 | Format.fprintf fmt "eval=%a;@." Disjunction.pp_ciset ctx.evaluated; |
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141 | b13a7d5f | xthirioux | Format.fprintf fmt "graph=%a;@." pp_dep_graph ctx.dep_graph; |

142 | 45c13277 | xthirioux | Format.fprintf fmt "disjoint=%a;@." Disjunction.pp_disjoint_map ctx.disjoint; |

143 | Format.fprintf fmt "policy=%a;@." pp_reuse_policy ctx.policy; |
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144 | Format.fprintf fmt "/* END context */ }@."; |
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145 | end |
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146 | |||

147 | a38c681e | xthirioux | (* computes the reusable dependencies of variable [var] in graph [g], |

148 | once [var] has been evaluated |
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149 | 45c13277 | xthirioux | - [locals] is the set of potentially reusable variables |

150 | - [evaluated] is the set of evaluated variables |
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151 | - [quasi] is the set of quasi-reusable variables |
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152 | - [reusable] is the set of dead/reusable dependencies of [var] in graph [g] |
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153 | - [policy] is the reuse map (which domain is [evaluated]) |
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154 | a38c681e | xthirioux | *) |

155 | b13a7d5f | xthirioux | let compute_dependencies heads ctx = |

156 | 45c13277 | xthirioux | begin |

157 | b13a7d5f | xthirioux | (*Log.report ~level:6 (fun fmt -> Format.fprintf fmt "compute_reusable_dependencies %a %a %a@." Disjunction.pp_ciset locals Printers.pp_var_name var pp_context ctx);*) |

158 | List.iter (kill_root ctx) heads; |
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159 | remove_roots ctx; |
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160 | 45c13277 | xthirioux | end |

161 | |||

162 | let compute_evaluated heads ctx = |
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163 | 695d6f2f | xthirioux | begin |

164 | 45c13277 | xthirioux | List.iter (fun head -> ctx.evaluated <- Disjunction.CISet.add head ctx.evaluated) heads; |

165 | 695d6f2f | xthirioux | end |

166 | |||

167 | b13a7d5f | xthirioux | let compute_reuse node ctx var = |

168 | 45c13277 | xthirioux | let aliasable = is_aliasable_input node var.var_id in |

169 | b13a7d5f | xthirioux | let disjoint = Hashtbl.find ctx.disjoint var.var_id in |

170 | let eligible v = |
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171 | Typing.eq_ground var.var_type v.var_type |
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172 | && not (aliasable v) in |
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173 | let locally_reusable v = |
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174 | IdentDepGraph.fold_pred (fun p r -> r && Disjunction.CISet.exists (fun d -> p = d.var_id) disjoint) ctx.dep_graph v.var_id true in |
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175 | let eligibles = Disjunction.CISet.filter eligible ctx.evaluated in |
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176 | let dead, live = Disjunction.CISet.partition locally_reusable eligibles in |
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177 | 45c13277 | xthirioux | try |

178 | b13a7d5f | xthirioux | let disjoint_live = Disjunction.CISet.inter disjoint live in |

179 | let reuse = Disjunction.CISet.max_elt disjoint_live in |
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180 | 45c13277 | xthirioux | begin |

181 | b13a7d5f | xthirioux | IdentDepGraph.add_edge ctx.dep_graph var.var_id reuse.var_id; |

182 | Hashtbl.add ctx.policy var.var_id (Hashtbl.find ctx.policy reuse.var_id); |
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183 | 45c13277 | xthirioux | end |

184 | with Not_found -> |
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185 | try |
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186 | b13a7d5f | xthirioux | let reuse = Disjunction.CISet.choose dead in |

187 | 45c13277 | xthirioux | begin |

188 | b13a7d5f | xthirioux | IdentDepGraph.add_edge ctx.dep_graph var.var_id reuse.var_id; |

189 | Hashtbl.add ctx.policy var.var_id (Hashtbl.find ctx.policy reuse.var_id); |
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190 | 45c13277 | xthirioux | end |

191 | with Not_found -> |
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192 | begin |
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193 | Hashtbl.add ctx.policy var.var_id var; |
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194 | end |
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195 | |||

196 | b6a94a4e | xthirioux | let compute_reuse_policy node schedule disjoint g = |

197 | let sort = ref schedule in |
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198 | 45c13277 | xthirioux | let ctx = { evaluated = Disjunction.CISet.empty; |

199 | b13a7d5f | xthirioux | dep_graph = g; |

200 | 45c13277 | xthirioux | disjoint = disjoint; |

201 | policy = Hashtbl.create 23; } in |
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202 | a38c681e | xthirioux | while !sort <> [] |

203 | b6a94a4e | xthirioux | do |

204 | 45c13277 | xthirioux | Log.report ~level:6 (fun fmt -> Format.fprintf fmt "new context:%a@." pp_context ctx); |

205 | let heads = List.map (fun v -> get_node_var v node) (List.hd !sort) in |
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206 | Log.report ~level:6 (fun fmt -> Format.fprintf fmt "NEW HEADS:"); |
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207 | b4d9710b | xthirioux | List.iter (fun head -> Log.report ~level:6 (fun fmt -> Format.fprintf fmt "%s " head.var_id)) heads; |

208 | 45c13277 | xthirioux | Log.report ~level:6 (fun fmt -> Format.fprintf fmt "@."); |

209 | Log.report ~level:6 (fun fmt -> Format.fprintf fmt "COMPUTE_DEPENDENCIES@."); |
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210 | b13a7d5f | xthirioux | compute_dependencies heads ctx; |

211 | 45c13277 | xthirioux | Log.report ~level:6 (fun fmt -> Format.fprintf fmt "new context:%a@." pp_context ctx); |

212 | Log.report ~level:6 (fun fmt -> Format.fprintf fmt "COMPUTE_REUSE@."); |
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213 | b13a7d5f | xthirioux | List.iter (compute_reuse node ctx) heads; |

214 | compute_evaluated heads ctx; |
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215 | 45c13277 | xthirioux | List.iter (fun head -> Log.report ~level:6 (fun fmt -> Format.fprintf fmt "reuse %s instead of %s@." (Hashtbl.find ctx.policy head.var_id).var_id head.var_id)) heads; |

216 | b6a94a4e | xthirioux | sort := List.tl !sort; |

217 | done; |
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218 | b13a7d5f | xthirioux | IdentDepGraph.clear ctx.dep_graph; |

219 | 45c13277 | xthirioux | ctx.policy |

220 | 7afcba5a | xthirioux | |

221 | (* Reuse policy: |
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222 | - could reuse variables with the same type exactly only (simple). |
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223 | - reusing variables with different types would involve: |
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224 | - either dirty castings |
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225 | - or complex inclusion expression (for instance: array <-> array cell, struct <-> struct field) to be able to reuse only some parts of structured data. |
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226 | ... it seems too complex and potentially unsafe |
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227 | 44bea83a | xthirioux | - for node instance calls: output variables could NOT reuse aliasable input variables, |

228 | 7afcba5a | xthirioux | even if inputs become dead, because the correctness would depend on the scheduling |

229 | of the callee (so, the compiling strategy could NOT be modular anymore). |
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230 | - once a policy is set, we need to: |
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231 | - replace each variable by its reuse alias. |
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232 | - simplify resulting equations, as we may now have: |
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233 | x = x; --> ; for scalar vars |
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234 | or: |
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235 | x = &{ f1 = x->f1; f2 = t; } --> x->f2 = t; for struct vars |
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236 | *) |
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237 | |||

238 | 695d6f2f | xthirioux | |

239 | bb2ca5f4 | xthirioux | (* the reuse policy seeks to use less local variables |

240 | by replacing local variables, applying the rules |
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241 | in the following order: |
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242 | 1) use another clock disjoint still live variable, |
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243 | with the greatest possible disjoint clock |
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244 | 2) reuse a dead variable |
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245 | For the sake of safety, we replace variables by others: |
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246 | - with the same type |
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247 | - not aliasable (i.e. address type) |
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248 | *) |
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249 | b6a94a4e | xthirioux | |

250 | 695d6f2f | xthirioux | (* Local Variables: *) |

251 | (* compile-command:"make -C .." *) |
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252 | (* End: *) |