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Optimization removes linear let-bindings of impure expressions
author Adam Chlipala <adamc@hcoop.net>
date Thu, 11 Sep 2008 11:30:39 -0400
parents 04ebfe929a98
children 1fd2a29a7c85
rev   line source
adamc@133 1 (* Copyright (c) 2008, Adam Chlipala
adamc@133 2 * All rights reserved.
adamc@133 3 *
adamc@133 4 * Redistribution and use in source and binary forms, with or without
adamc@133 5 * modification, are permitted provided that the following conditions are met:
adamc@133 6 *
adamc@133 7 * - Redistributions of source code must retain the above copyright notice,
adamc@133 8 * this list of conditions and the following disclaimer.
adamc@133 9 * - Redistributions in binary form must reproduce the above copyright notice,
adamc@133 10 * this list of conditions and the following disclaimer in the documentation
adamc@133 11 * and/or other materials provided with the distribution.
adamc@133 12 * - The names of contributors may not be used to endorse or promote products
adamc@133 13 * derived from this software without specific prior written permission.
adamc@133 14 *
adamc@133 15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
adamc@133 16 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
adamc@133 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
adamc@133 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
adamc@133 19 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
adamc@133 20 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
adamc@133 21 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
adamc@133 22 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
adamc@133 23 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
adamc@133 24 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
adamc@133 25 * POSSIBILITY OF SUCH DAMAGE.
adamc@133 26 *)
adamc@133 27
adamc@133 28 (* Simplify a Mono program algebraically *)
adamc@133 29
adamc@133 30 structure MonoReduce :> MONO_REDUCE = struct
adamc@133 31
adamc@133 32 open Mono
adamc@133 33
adamc@133 34 structure E = MonoEnv
adamc@133 35 structure U = MonoUtil
adamc@133 36
adamc@133 37
adamc@252 38 fun impure (e, _) =
adamc@252 39 case e of
adamc@252 40 EWrite _ => true
adamc@252 41 | EQuery _ => true
adamc@307 42 | EDml _ => true
adamc@252 43 | EAbs _ => false
adamc@252 44
adamc@252 45 | EPrim _ => false
adamc@252 46 | ERel _ => false
adamc@252 47 | ENamed _ => false
adamc@252 48 | ECon (_, _, eo) => (case eo of NONE => false | SOME e => impure e)
adamc@297 49 | ENone _ => false
adamc@290 50 | ESome (_, e) => impure e
adamc@252 51 | EFfi _ => false
adamc@252 52 | EFfiApp _ => false
adamc@252 53 | EApp ((EFfi _, _), _) => false
adamc@252 54 | EApp _ => true
adamc@252 55
adamc@252 56 | ERecord xes => List.exists (fn (_, e, _) => impure e) xes
adamc@252 57 | EField (e, _) => impure e
adamc@252 58
adamc@252 59 | ECase (e, pes, _) => impure e orelse List.exists (fn (_, e) => impure e) pes
adamc@252 60
adamc@283 61 | EError (e, _) => impure e
adamc@283 62
adamc@252 63 | EStrcat (e1, e2) => impure e1 orelse impure e2
adamc@252 64
adamc@252 65 | ESeq (e1, e2) => impure e1 orelse impure e2
adamc@252 66 | ELet (_, _, e1, e2) => impure e1 orelse impure e2
adamc@252 67
adamc@252 68 | EClosure (_, es) => List.exists impure es
adamc@252 69
adamc@252 70
adamc@252 71 val liftExpInExp = Monoize.liftExpInExp
adamc@252 72
adamc@252 73 val subExpInExp' =
adamc@133 74 U.Exp.mapB {typ = fn t => t,
adamc@133 75 exp = fn (xn, rep) => fn e =>
adamc@133 76 case e of
adamc@133 77 ERel xn' =>
adamc@133 78 (case Int.compare (xn', xn) of
adamc@133 79 EQUAL => #1 rep
adamc@133 80 | GREATER=> ERel (xn' - 1)
adamc@133 81 | LESS => e)
adamc@133 82 | _ => e,
adamc@133 83 bind = fn ((xn, rep), U.Exp.RelE _) => (xn+1, liftExpInExp 0 rep)
adamc@133 84 | (ctx, _) => ctx}
adamc@133 85
adamc@252 86 fun subExpInExp (n, e1) e2 =
adamc@252 87 let
adamc@252 88 val r = subExpInExp' (n, e1) e2
adamc@252 89 in
adamc@252 90 (*Print.prefaces "subExpInExp" [("e1", MonoPrint.p_exp MonoEnv.empty e1),
adamc@252 91 ("e2", MonoPrint.p_exp MonoEnv.empty e2),
adamc@252 92 ("r", MonoPrint.p_exp MonoEnv.empty r)];*)
adamc@252 93 r
adamc@252 94 end
adamc@133 95
adamc@133 96 fun typ c = c
adamc@133 97
adamc@316 98 val swapExpVars =
adamc@316 99 U.Exp.mapB {typ = fn t => t,
adamc@316 100 exp = fn lower => fn e =>
adamc@316 101 case e of
adamc@316 102 ERel xn =>
adamc@316 103 if xn = lower then
adamc@316 104 ERel (lower + 1)
adamc@316 105 else if xn = lower + 1 then
adamc@316 106 ERel lower
adamc@316 107 else
adamc@316 108 e
adamc@316 109 | _ => e,
adamc@316 110 bind = fn (lower, U.Exp.RelE _) => lower+1
adamc@316 111 | (lower, _) => lower}
adamc@316 112
adamc@258 113 datatype result = Yes of E.env | No | Maybe
adamc@258 114
adamc@183 115 fun match (env, p : pat, e : exp) =
adamc@183 116 case (#1 p, #1 e) of
adamc@258 117 (PWild, _) => Yes env
adamc@258 118 | (PVar (x, t), _) => Yes (E.pushERel env x t (SOME e))
adamc@183 119
adamc@280 120 | (PPrim (Prim.String s), EStrcat ((EPrim (Prim.String s'), _), _)) =>
adamc@280 121 if String.isPrefix s' s then
adamc@280 122 Maybe
adamc@280 123 else
adamc@280 124 No
adamc@280 125
adamc@183 126 | (PPrim p, EPrim p') =>
adamc@183 127 if Prim.equal (p, p') then
adamc@258 128 Yes env
adamc@183 129 else
adamc@258 130 No
adamc@183 131
adamc@188 132 | (PCon (_, PConVar n1, NONE), ECon (_, PConVar n2, NONE)) =>
adamc@183 133 if n1 = n2 then
adamc@258 134 Yes env
adamc@183 135 else
adamc@258 136 No
adamc@183 137
adamc@188 138 | (PCon (_, PConVar n1, SOME p), ECon (_, PConVar n2, SOME e)) =>
adamc@183 139 if n1 = n2 then
adamc@183 140 match (env, p, e)
adamc@183 141 else
adamc@258 142 No
adamc@183 143
adamc@188 144 | (PCon (_, PConFfi {mod = m1, con = con1, ...}, NONE), ECon (_, PConFfi {mod = m2, con = con2, ...}, NONE)) =>
adamc@185 145 if m1 = m2 andalso con1 = con2 then
adamc@258 146 Yes env
adamc@185 147 else
adamc@258 148 No
adamc@185 149
adamc@188 150 | (PCon (_, PConFfi {mod = m1, con = con1, ...}, SOME ep), ECon (_, PConFfi {mod = m2, con = con2, ...}, SOME e)) =>
adamc@185 151 if m1 = m2 andalso con1 = con2 then
adamc@185 152 match (env, p, e)
adamc@185 153 else
adamc@258 154 No
adamc@185 155
adamc@183 156 | (PRecord xps, ERecord xes) =>
adamc@183 157 let
adamc@183 158 fun consider (xps, env) =
adamc@183 159 case xps of
adamc@258 160 [] => Yes env
adamc@183 161 | (x, p, _) :: rest =>
adamc@183 162 case List.find (fn (x', _, _) => x' = x) xes of
adamc@258 163 NONE => No
adamc@183 164 | SOME (_, e, _) =>
adamc@183 165 case match (env, p, e) of
adamc@258 166 No => No
adamc@258 167 | Maybe => Maybe
adamc@258 168 | Yes env => consider (rest, env)
adamc@183 169 in
adamc@183 170 consider (xps, env)
adamc@183 171 end
adamc@183 172
adamc@258 173 | _ => Maybe
adamc@183 174
adamc@318 175 datatype event =
adamc@318 176 WritePage
adamc@318 177 | ReadDb
adamc@318 178 | WriteDb
adamc@318 179 | UseRel of int
adamc@318 180 | Unsure
adamc@318 181
adamc@318 182 fun p_event e =
adamc@318 183 let
adamc@318 184 open Print.PD
adamc@318 185 in
adamc@318 186 case e of
adamc@318 187 WritePage => string "WritePage"
adamc@318 188 | ReadDb => string "ReadDb"
adamc@318 189 | WriteDb => string "WriteDb"
adamc@318 190 | UseRel n => string ("UseRel" ^ Int.toString n)
adamc@318 191 | Unsure => string "Unsure"
adamc@318 192 end
adamc@318 193
adamc@318 194 fun patBinds (p, _) =
adamc@318 195 case p of
adamc@318 196 PWild => 0
adamc@318 197 | PVar _ => 1
adamc@318 198 | PPrim _ => 0
adamc@318 199 | PCon (_, _, NONE) => 0
adamc@318 200 | PCon (_, _, SOME p) => patBinds p
adamc@318 201 | PRecord xpts => foldl (fn ((_, p, _), n) => n + patBinds p) 0 xpts
adamc@318 202 | PNone _ => 0
adamc@318 203 | PSome (_, p) => patBinds p
adamc@318 204
adamc@318 205 fun summarize d (e, _) =
adamc@318 206 case e of
adamc@318 207 EPrim _ => []
adamc@318 208 | ERel n => if n >= d then [UseRel (n - d)] else []
adamc@318 209 | ENamed _ => []
adamc@318 210 | ECon (_, _, NONE) => []
adamc@318 211 | ECon (_, _, SOME e) => summarize d e
adamc@318 212 | ENone _ => []
adamc@318 213 | ESome (_, e) => summarize d e
adamc@318 214 | EFfi _ => []
adamc@318 215 | EFfiApp (_, _, es) => List.concat (map (summarize d) es)
adamc@318 216 | EApp _ => [Unsure]
adamc@318 217 | EAbs _ => []
adamc@318 218
adamc@318 219 | ERecord xets => List.concat (map (summarize d o #2) xets)
adamc@318 220 | EField (e, _) => summarize d e
adamc@318 221
adamc@318 222 | ECase (e, pes, _) =>
adamc@318 223 let
adamc@318 224 val lss = map (fn (p, e) => summarize (d + patBinds p) e) pes
adamc@318 225 in
adamc@318 226 case lss of
adamc@318 227 [] => raise Fail "Empty pattern match"
adamc@318 228 | ls :: lss =>
adamc@318 229 if List.all (fn ls' => ls' = ls) lss then
adamc@318 230 summarize d e @ ls
adamc@318 231 else
adamc@318 232 [Unsure]
adamc@318 233 end
adamc@318 234 | EStrcat (e1, e2) => summarize d e1 @ summarize d e2
adamc@318 235
adamc@318 236 | EError (e, _) => summarize d e @ [Unsure]
adamc@318 237
adamc@318 238 | EWrite e => summarize d e @ [WritePage]
adamc@318 239
adamc@318 240 | ESeq (e1, e2) => summarize d e1 @ summarize d e2
adamc@318 241 | ELet (_, _, e1, e2) => summarize d e1 @ summarize (d + 1) e2
adamc@318 242
adamc@318 243 | EClosure (_, es) => List.concat (map (summarize d) es)
adamc@318 244
adamc@318 245 | EQuery {query, body, initial, ...} =>
adamc@318 246 List.concat [summarize d query,
adamc@318 247 summarize d body,
adamc@318 248 summarize d initial,
adamc@318 249 [ReadDb]]
adamc@318 250
adamc@318 251 | EDml e => summarize d e @ [WriteDb]
adamc@318 252
adamc@133 253 fun exp env e =
adamc@133 254 case e of
adamc@183 255 ERel n =>
adamc@183 256 (case E.lookupERel env n of
adamc@183 257 (_, _, SOME e') => #1 e'
adamc@183 258 | _ => e)
adamc@183 259 | ENamed n =>
adamc@133 260 (case E.lookupENamed env n of
adamc@133 261 (_, _, SOME e', _) => #1 e'
adamc@133 262 | _ => e)
adamc@133 263
adamc@252 264 | EApp ((EAbs (x, t, _, e1), loc), e2) =>
adamc@252 265 ((*Print.prefaces "Considering" [("e1", MonoPrint.p_exp env e1),
adamc@252 266 ("e2", MonoPrint.p_exp env e2)];*)
adamc@252 267 if impure e2 then
adamc@252 268 #1 (reduceExp env (ELet (x, t, e2, e1), loc))
adamc@252 269 else
adamc@252 270 #1 (reduceExp env (subExpInExp (0, e2) e1)))
adamc@133 271
adamc@184 272 | ECase (disc, pes, _) =>
adamc@258 273 let
adamc@258 274 fun search pes =
adamc@258 275 case pes of
adamc@258 276 [] => e
adamc@258 277 | (p, body) :: pes =>
adamc@258 278 case match (env, p, disc) of
adamc@258 279 No => search pes
adamc@258 280 | Maybe => e
adamc@258 281 | Yes env => #1 (reduceExp env body)
adamc@258 282 in
adamc@258 283 search pes
adamc@258 284 end
adamc@183 285
adamc@252 286 | EField ((ERecord xes, _), x) =>
adamc@252 287 (case List.find (fn (x', _, _) => x' = x) xes of
adamc@252 288 SOME (_, e, _) => #1 e
adamc@252 289 | NONE => e)
adamc@252 290
adamc@252 291 | ELet (x1, t1, (ELet (x2, t2, e1, b1), loc), b2) =>
adamc@252 292 let
adamc@252 293 val e' = (ELet (x2, t2, e1,
adamc@252 294 (ELet (x1, t1, b1,
adamc@252 295 liftExpInExp 1 b2), loc)), loc)
adamc@252 296 in
adamc@253 297 (*Print.prefaces "ELet commute" [("e", MonoPrint.p_exp env (e, loc)),
adamc@253 298 ("e'", MonoPrint.p_exp env e')];*)
adamc@252 299 #1 (reduceExp env e')
adamc@252 300 end
adamc@252 301 | EApp ((ELet (x, t, e, b), loc), e') =>
adamc@252 302 #1 (reduceExp env (ELet (x, t, e,
adamc@252 303 (EApp (b, liftExpInExp 0 e'), loc)), loc))
adamc@316 304
adamc@316 305 | ELet (x, t, e, (EAbs (x', t' as (TRecord [], _), ran, e'), loc)) =>
adamc@316 306 EAbs (x', t', ran, (ELet (x, t, liftExpInExp 0 e, swapExpVars 0 e'), loc))
adamc@316 307
adamc@252 308 | ELet (x, t, e', b) =>
adamc@252 309 if impure e' then
adamc@318 310 let
adamc@318 311 val effs_e' = summarize 0 e'
adamc@318 312 val effs_b = summarize 0 b
adamc@318 313
adamc@318 314 fun does eff = List.exists (fn eff' => eff' = eff) effs_e'
adamc@318 315 val writesPage = does WritePage
adamc@318 316 val readsDb = does ReadDb
adamc@318 317 val writesDb = does WriteDb
adamc@318 318
adamc@318 319 fun verifyUnused eff =
adamc@318 320 case eff of
adamc@318 321 UseRel r => r <> 0
adamc@318 322 | Unsure => false
adamc@318 323 | _ => true
adamc@318 324
adamc@318 325 fun verifyCompatible effs =
adamc@318 326 case effs of
adamc@318 327 [] => false
adamc@318 328 | eff :: effs =>
adamc@318 329 case eff of
adamc@318 330 Unsure => false
adamc@318 331 | UseRel r =>
adamc@318 332 if r = 0 then
adamc@318 333 List.all verifyUnused effs
adamc@318 334 else
adamc@318 335 verifyCompatible effs
adamc@318 336 | WritePage => not writesPage andalso verifyCompatible effs
adamc@318 337 | ReadDb => not writesDb andalso verifyCompatible effs
adamc@318 338 | WriteDb => not writesDb andalso not readsDb andalso verifyCompatible effs
adamc@318 339 in
adamc@318 340 (*Print.prefaces "verifyCompatible"
adamc@318 341 [("e'", MonoPrint.p_exp env e'),
adamc@318 342 ("b", MonoPrint.p_exp (E.pushERel env x t NONE) b),
adamc@318 343 ("effs_e'", Print.p_list p_event effs_e'),
adamc@318 344 ("effs_b", Print.p_list p_event effs_b)];*)
adamc@318 345 if verifyCompatible effs_b then
adamc@318 346 #1 (reduceExp env (subExpInExp (0, e') b))
adamc@318 347 else
adamc@318 348 e
adamc@318 349 end
adamc@252 350 else
adamc@252 351 #1 (reduceExp env (subExpInExp (0, e') b))
adamc@252 352
adamc@268 353 | EStrcat ((EPrim (Prim.String s1), _), (EPrim (Prim.String s2), _)) =>
adamc@268 354 EPrim (Prim.String (s1 ^ s2))
adamc@268 355
adamc@133 356 | _ => e
adamc@133 357
adamc@252 358 and bind (env, b) =
adamc@252 359 case b of
adamc@252 360 U.Decl.Datatype (x, n, xncs) => E.pushDatatype env x n xncs
adamc@252 361 | U.Decl.RelE (x, t) => E.pushERel env x t NONE
adamc@252 362 | U.Decl.NamedE (x, n, t, eo, s) => E.pushENamed env x n t (Option.map (reduceExp env) eo) s
adamc@252 363
adamc@133 364 and reduceExp env = U.Exp.mapB {typ = typ, exp = exp, bind = bind} env
adamc@133 365
adamc@133 366 fun decl env d = d
adamc@133 367
adamc@133 368 val reduce = U.File.mapB {typ = typ, exp = exp, decl = decl, bind = bind} E.empty
adamc@133 369
adamc@133 370 end