Dan Willemsen | cc753b7 | 2021-08-31 13:25:42 -0700 | [diff] [blame] | 1 | // Copyright 2009 The Go Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | package walk |
| 6 | |
| 7 | import ( |
| 8 | "go/constant" |
| 9 | "go/token" |
| 10 | "sort" |
| 11 | |
| 12 | "cmd/compile/internal/base" |
| 13 | "cmd/compile/internal/ir" |
| 14 | "cmd/compile/internal/typecheck" |
| 15 | "cmd/compile/internal/types" |
| 16 | "cmd/internal/src" |
| 17 | ) |
| 18 | |
| 19 | // walkSwitch walks a switch statement. |
| 20 | func walkSwitch(sw *ir.SwitchStmt) { |
| 21 | // Guard against double walk, see #25776. |
| 22 | if sw.Walked() { |
| 23 | return // Was fatal, but eliminating every possible source of double-walking is hard |
| 24 | } |
| 25 | sw.SetWalked(true) |
| 26 | |
| 27 | if sw.Tag != nil && sw.Tag.Op() == ir.OTYPESW { |
| 28 | walkSwitchType(sw) |
| 29 | } else { |
| 30 | walkSwitchExpr(sw) |
| 31 | } |
| 32 | } |
| 33 | |
| 34 | // walkSwitchExpr generates an AST implementing sw. sw is an |
| 35 | // expression switch. |
| 36 | func walkSwitchExpr(sw *ir.SwitchStmt) { |
| 37 | lno := ir.SetPos(sw) |
| 38 | |
| 39 | cond := sw.Tag |
| 40 | sw.Tag = nil |
| 41 | |
| 42 | // convert switch {...} to switch true {...} |
| 43 | if cond == nil { |
| 44 | cond = ir.NewBool(true) |
| 45 | cond = typecheck.Expr(cond) |
| 46 | cond = typecheck.DefaultLit(cond, nil) |
| 47 | } |
| 48 | |
| 49 | // Given "switch string(byteslice)", |
| 50 | // with all cases being side-effect free, |
| 51 | // use a zero-cost alias of the byte slice. |
| 52 | // Do this before calling walkExpr on cond, |
| 53 | // because walkExpr will lower the string |
| 54 | // conversion into a runtime call. |
| 55 | // See issue 24937 for more discussion. |
| 56 | if cond.Op() == ir.OBYTES2STR && allCaseExprsAreSideEffectFree(sw) { |
| 57 | cond := cond.(*ir.ConvExpr) |
| 58 | cond.SetOp(ir.OBYTES2STRTMP) |
| 59 | } |
| 60 | |
| 61 | cond = walkExpr(cond, sw.PtrInit()) |
| 62 | if cond.Op() != ir.OLITERAL && cond.Op() != ir.ONIL { |
| 63 | cond = copyExpr(cond, cond.Type(), &sw.Compiled) |
| 64 | } |
| 65 | |
| 66 | base.Pos = lno |
| 67 | |
| 68 | s := exprSwitch{ |
| 69 | exprname: cond, |
| 70 | } |
| 71 | |
| 72 | var defaultGoto ir.Node |
| 73 | var body ir.Nodes |
| 74 | for _, ncase := range sw.Cases { |
| 75 | label := typecheck.AutoLabel(".s") |
| 76 | jmp := ir.NewBranchStmt(ncase.Pos(), ir.OGOTO, label) |
| 77 | |
| 78 | // Process case dispatch. |
| 79 | if len(ncase.List) == 0 { |
| 80 | if defaultGoto != nil { |
| 81 | base.Fatalf("duplicate default case not detected during typechecking") |
| 82 | } |
| 83 | defaultGoto = jmp |
| 84 | } |
| 85 | |
| 86 | for _, n1 := range ncase.List { |
| 87 | s.Add(ncase.Pos(), n1, jmp) |
| 88 | } |
| 89 | |
| 90 | // Process body. |
| 91 | body.Append(ir.NewLabelStmt(ncase.Pos(), label)) |
| 92 | body.Append(ncase.Body...) |
| 93 | if fall, pos := endsInFallthrough(ncase.Body); !fall { |
| 94 | br := ir.NewBranchStmt(base.Pos, ir.OBREAK, nil) |
| 95 | br.SetPos(pos) |
| 96 | body.Append(br) |
| 97 | } |
| 98 | } |
| 99 | sw.Cases = nil |
| 100 | |
| 101 | if defaultGoto == nil { |
| 102 | br := ir.NewBranchStmt(base.Pos, ir.OBREAK, nil) |
| 103 | br.SetPos(br.Pos().WithNotStmt()) |
| 104 | defaultGoto = br |
| 105 | } |
| 106 | |
| 107 | s.Emit(&sw.Compiled) |
| 108 | sw.Compiled.Append(defaultGoto) |
| 109 | sw.Compiled.Append(body.Take()...) |
| 110 | walkStmtList(sw.Compiled) |
| 111 | } |
| 112 | |
| 113 | // An exprSwitch walks an expression switch. |
| 114 | type exprSwitch struct { |
| 115 | exprname ir.Node // value being switched on |
| 116 | |
| 117 | done ir.Nodes |
| 118 | clauses []exprClause |
| 119 | } |
| 120 | |
| 121 | type exprClause struct { |
| 122 | pos src.XPos |
| 123 | lo, hi ir.Node |
| 124 | jmp ir.Node |
| 125 | } |
| 126 | |
| 127 | func (s *exprSwitch) Add(pos src.XPos, expr, jmp ir.Node) { |
| 128 | c := exprClause{pos: pos, lo: expr, hi: expr, jmp: jmp} |
| 129 | if types.IsOrdered[s.exprname.Type().Kind()] && expr.Op() == ir.OLITERAL { |
| 130 | s.clauses = append(s.clauses, c) |
| 131 | return |
| 132 | } |
| 133 | |
| 134 | s.flush() |
| 135 | s.clauses = append(s.clauses, c) |
| 136 | s.flush() |
| 137 | } |
| 138 | |
| 139 | func (s *exprSwitch) Emit(out *ir.Nodes) { |
| 140 | s.flush() |
| 141 | out.Append(s.done.Take()...) |
| 142 | } |
| 143 | |
| 144 | func (s *exprSwitch) flush() { |
| 145 | cc := s.clauses |
| 146 | s.clauses = nil |
| 147 | if len(cc) == 0 { |
| 148 | return |
| 149 | } |
| 150 | |
| 151 | // Caution: If len(cc) == 1, then cc[0] might not an OLITERAL. |
| 152 | // The code below is structured to implicitly handle this case |
| 153 | // (e.g., sort.Slice doesn't need to invoke the less function |
| 154 | // when there's only a single slice element). |
| 155 | |
| 156 | if s.exprname.Type().IsString() && len(cc) >= 2 { |
| 157 | // Sort strings by length and then by value. It is |
| 158 | // much cheaper to compare lengths than values, and |
| 159 | // all we need here is consistency. We respect this |
| 160 | // sorting below. |
| 161 | sort.Slice(cc, func(i, j int) bool { |
| 162 | si := ir.StringVal(cc[i].lo) |
| 163 | sj := ir.StringVal(cc[j].lo) |
| 164 | if len(si) != len(sj) { |
| 165 | return len(si) < len(sj) |
| 166 | } |
| 167 | return si < sj |
| 168 | }) |
| 169 | |
| 170 | // runLen returns the string length associated with a |
| 171 | // particular run of exprClauses. |
| 172 | runLen := func(run []exprClause) int64 { return int64(len(ir.StringVal(run[0].lo))) } |
| 173 | |
| 174 | // Collapse runs of consecutive strings with the same length. |
| 175 | var runs [][]exprClause |
| 176 | start := 0 |
| 177 | for i := 1; i < len(cc); i++ { |
| 178 | if runLen(cc[start:]) != runLen(cc[i:]) { |
| 179 | runs = append(runs, cc[start:i]) |
| 180 | start = i |
| 181 | } |
| 182 | } |
| 183 | runs = append(runs, cc[start:]) |
| 184 | |
| 185 | // Perform two-level binary search. |
| 186 | binarySearch(len(runs), &s.done, |
| 187 | func(i int) ir.Node { |
| 188 | return ir.NewBinaryExpr(base.Pos, ir.OLE, ir.NewUnaryExpr(base.Pos, ir.OLEN, s.exprname), ir.NewInt(runLen(runs[i-1]))) |
| 189 | }, |
| 190 | func(i int, nif *ir.IfStmt) { |
| 191 | run := runs[i] |
| 192 | nif.Cond = ir.NewBinaryExpr(base.Pos, ir.OEQ, ir.NewUnaryExpr(base.Pos, ir.OLEN, s.exprname), ir.NewInt(runLen(run))) |
| 193 | s.search(run, &nif.Body) |
| 194 | }, |
| 195 | ) |
| 196 | return |
| 197 | } |
| 198 | |
| 199 | sort.Slice(cc, func(i, j int) bool { |
| 200 | return constant.Compare(cc[i].lo.Val(), token.LSS, cc[j].lo.Val()) |
| 201 | }) |
| 202 | |
| 203 | // Merge consecutive integer cases. |
| 204 | if s.exprname.Type().IsInteger() { |
| 205 | consecutive := func(last, next constant.Value) bool { |
| 206 | delta := constant.BinaryOp(next, token.SUB, last) |
| 207 | return constant.Compare(delta, token.EQL, constant.MakeInt64(1)) |
| 208 | } |
| 209 | |
| 210 | merged := cc[:1] |
| 211 | for _, c := range cc[1:] { |
| 212 | last := &merged[len(merged)-1] |
| 213 | if last.jmp == c.jmp && consecutive(last.hi.Val(), c.lo.Val()) { |
| 214 | last.hi = c.lo |
| 215 | } else { |
| 216 | merged = append(merged, c) |
| 217 | } |
| 218 | } |
| 219 | cc = merged |
| 220 | } |
| 221 | |
| 222 | s.search(cc, &s.done) |
| 223 | } |
| 224 | |
| 225 | func (s *exprSwitch) search(cc []exprClause, out *ir.Nodes) { |
| 226 | binarySearch(len(cc), out, |
| 227 | func(i int) ir.Node { |
| 228 | return ir.NewBinaryExpr(base.Pos, ir.OLE, s.exprname, cc[i-1].hi) |
| 229 | }, |
| 230 | func(i int, nif *ir.IfStmt) { |
| 231 | c := &cc[i] |
| 232 | nif.Cond = c.test(s.exprname) |
| 233 | nif.Body = []ir.Node{c.jmp} |
| 234 | }, |
| 235 | ) |
| 236 | } |
| 237 | |
| 238 | func (c *exprClause) test(exprname ir.Node) ir.Node { |
| 239 | // Integer range. |
| 240 | if c.hi != c.lo { |
| 241 | low := ir.NewBinaryExpr(c.pos, ir.OGE, exprname, c.lo) |
| 242 | high := ir.NewBinaryExpr(c.pos, ir.OLE, exprname, c.hi) |
| 243 | return ir.NewLogicalExpr(c.pos, ir.OANDAND, low, high) |
| 244 | } |
| 245 | |
| 246 | // Optimize "switch true { ...}" and "switch false { ... }". |
| 247 | if ir.IsConst(exprname, constant.Bool) && !c.lo.Type().IsInterface() { |
| 248 | if ir.BoolVal(exprname) { |
| 249 | return c.lo |
| 250 | } else { |
| 251 | return ir.NewUnaryExpr(c.pos, ir.ONOT, c.lo) |
| 252 | } |
| 253 | } |
| 254 | |
| 255 | return ir.NewBinaryExpr(c.pos, ir.OEQ, exprname, c.lo) |
| 256 | } |
| 257 | |
| 258 | func allCaseExprsAreSideEffectFree(sw *ir.SwitchStmt) bool { |
| 259 | // In theory, we could be more aggressive, allowing any |
| 260 | // side-effect-free expressions in cases, but it's a bit |
| 261 | // tricky because some of that information is unavailable due |
| 262 | // to the introduction of temporaries during order. |
| 263 | // Restricting to constants is simple and probably powerful |
| 264 | // enough. |
| 265 | |
| 266 | for _, ncase := range sw.Cases { |
| 267 | for _, v := range ncase.List { |
| 268 | if v.Op() != ir.OLITERAL { |
| 269 | return false |
| 270 | } |
| 271 | } |
| 272 | } |
| 273 | return true |
| 274 | } |
| 275 | |
| 276 | // endsInFallthrough reports whether stmts ends with a "fallthrough" statement. |
| 277 | func endsInFallthrough(stmts []ir.Node) (bool, src.XPos) { |
| 278 | // Search backwards for the index of the fallthrough |
| 279 | // statement. Do not assume it'll be in the last |
| 280 | // position, since in some cases (e.g. when the statement |
| 281 | // list contains autotmp_ variables), one or more OVARKILL |
| 282 | // nodes will be at the end of the list. |
| 283 | |
| 284 | i := len(stmts) - 1 |
| 285 | for i >= 0 && stmts[i].Op() == ir.OVARKILL { |
| 286 | i-- |
| 287 | } |
| 288 | if i < 0 { |
| 289 | return false, src.NoXPos |
| 290 | } |
| 291 | return stmts[i].Op() == ir.OFALL, stmts[i].Pos() |
| 292 | } |
| 293 | |
| 294 | // walkSwitchType generates an AST that implements sw, where sw is a |
| 295 | // type switch. |
| 296 | func walkSwitchType(sw *ir.SwitchStmt) { |
| 297 | var s typeSwitch |
| 298 | s.facename = sw.Tag.(*ir.TypeSwitchGuard).X |
| 299 | sw.Tag = nil |
| 300 | |
| 301 | s.facename = walkExpr(s.facename, sw.PtrInit()) |
| 302 | s.facename = copyExpr(s.facename, s.facename.Type(), &sw.Compiled) |
| 303 | s.okname = typecheck.Temp(types.Types[types.TBOOL]) |
| 304 | |
| 305 | // Get interface descriptor word. |
| 306 | // For empty interfaces this will be the type. |
| 307 | // For non-empty interfaces this will be the itab. |
| 308 | itab := ir.NewUnaryExpr(base.Pos, ir.OITAB, s.facename) |
| 309 | |
| 310 | // For empty interfaces, do: |
| 311 | // if e._type == nil { |
| 312 | // do nil case if it exists, otherwise default |
| 313 | // } |
| 314 | // h := e._type.hash |
| 315 | // Use a similar strategy for non-empty interfaces. |
| 316 | ifNil := ir.NewIfStmt(base.Pos, nil, nil, nil) |
| 317 | ifNil.Cond = ir.NewBinaryExpr(base.Pos, ir.OEQ, itab, typecheck.NodNil()) |
| 318 | base.Pos = base.Pos.WithNotStmt() // disable statement marks after the first check. |
| 319 | ifNil.Cond = typecheck.Expr(ifNil.Cond) |
| 320 | ifNil.Cond = typecheck.DefaultLit(ifNil.Cond, nil) |
| 321 | // ifNil.Nbody assigned at end. |
| 322 | sw.Compiled.Append(ifNil) |
| 323 | |
| 324 | // Load hash from type or itab. |
| 325 | dotHash := typeHashFieldOf(base.Pos, itab) |
| 326 | s.hashname = copyExpr(dotHash, dotHash.Type(), &sw.Compiled) |
| 327 | |
| 328 | br := ir.NewBranchStmt(base.Pos, ir.OBREAK, nil) |
| 329 | var defaultGoto, nilGoto ir.Node |
| 330 | var body ir.Nodes |
| 331 | for _, ncase := range sw.Cases { |
| 332 | caseVar := ncase.Var |
| 333 | |
| 334 | // For single-type cases with an interface type, |
| 335 | // we initialize the case variable as part of the type assertion. |
| 336 | // In other cases, we initialize it in the body. |
| 337 | var singleType *types.Type |
| 338 | if len(ncase.List) == 1 && ncase.List[0].Op() == ir.OTYPE { |
| 339 | singleType = ncase.List[0].Type() |
| 340 | } |
| 341 | caseVarInitialized := false |
| 342 | |
| 343 | label := typecheck.AutoLabel(".s") |
| 344 | jmp := ir.NewBranchStmt(ncase.Pos(), ir.OGOTO, label) |
| 345 | |
| 346 | if len(ncase.List) == 0 { // default: |
| 347 | if defaultGoto != nil { |
| 348 | base.Fatalf("duplicate default case not detected during typechecking") |
| 349 | } |
| 350 | defaultGoto = jmp |
| 351 | } |
| 352 | |
| 353 | for _, n1 := range ncase.List { |
| 354 | if ir.IsNil(n1) { // case nil: |
| 355 | if nilGoto != nil { |
| 356 | base.Fatalf("duplicate nil case not detected during typechecking") |
| 357 | } |
| 358 | nilGoto = jmp |
| 359 | continue |
| 360 | } |
| 361 | |
| 362 | if singleType != nil && singleType.IsInterface() { |
Dan Willemsen | bc60c3c | 2021-12-15 01:09:00 -0800 | [diff] [blame] | 363 | s.Add(ncase.Pos(), n1, caseVar, jmp) |
Dan Willemsen | cc753b7 | 2021-08-31 13:25:42 -0700 | [diff] [blame] | 364 | caseVarInitialized = true |
| 365 | } else { |
Dan Willemsen | bc60c3c | 2021-12-15 01:09:00 -0800 | [diff] [blame] | 366 | s.Add(ncase.Pos(), n1, nil, jmp) |
Dan Willemsen | cc753b7 | 2021-08-31 13:25:42 -0700 | [diff] [blame] | 367 | } |
| 368 | } |
| 369 | |
| 370 | body.Append(ir.NewLabelStmt(ncase.Pos(), label)) |
| 371 | if caseVar != nil && !caseVarInitialized { |
| 372 | val := s.facename |
| 373 | if singleType != nil { |
| 374 | // We have a single concrete type. Extract the data. |
| 375 | if singleType.IsInterface() { |
| 376 | base.Fatalf("singleType interface should have been handled in Add") |
| 377 | } |
| 378 | val = ifaceData(ncase.Pos(), s.facename, singleType) |
| 379 | } |
Dan Willemsen | bc60c3c | 2021-12-15 01:09:00 -0800 | [diff] [blame] | 380 | if len(ncase.List) == 1 && ncase.List[0].Op() == ir.ODYNAMICTYPE { |
| 381 | dt := ncase.List[0].(*ir.DynamicType) |
| 382 | x := ir.NewDynamicTypeAssertExpr(ncase.Pos(), ir.ODYNAMICDOTTYPE, val, dt.X) |
| 383 | if dt.ITab != nil { |
| 384 | // TODO: make ITab a separate field in DynamicTypeAssertExpr? |
| 385 | x.T = dt.ITab |
| 386 | } |
| 387 | x.SetType(caseVar.Type()) |
| 388 | x.SetTypecheck(1) |
| 389 | val = x |
| 390 | } |
Dan Willemsen | cc753b7 | 2021-08-31 13:25:42 -0700 | [diff] [blame] | 391 | l := []ir.Node{ |
| 392 | ir.NewDecl(ncase.Pos(), ir.ODCL, caseVar), |
| 393 | ir.NewAssignStmt(ncase.Pos(), caseVar, val), |
| 394 | } |
| 395 | typecheck.Stmts(l) |
| 396 | body.Append(l...) |
| 397 | } |
| 398 | body.Append(ncase.Body...) |
| 399 | body.Append(br) |
| 400 | } |
| 401 | sw.Cases = nil |
| 402 | |
| 403 | if defaultGoto == nil { |
| 404 | defaultGoto = br |
| 405 | } |
| 406 | if nilGoto == nil { |
| 407 | nilGoto = defaultGoto |
| 408 | } |
| 409 | ifNil.Body = []ir.Node{nilGoto} |
| 410 | |
| 411 | s.Emit(&sw.Compiled) |
| 412 | sw.Compiled.Append(defaultGoto) |
| 413 | sw.Compiled.Append(body.Take()...) |
| 414 | |
| 415 | walkStmtList(sw.Compiled) |
| 416 | } |
| 417 | |
| 418 | // typeHashFieldOf returns an expression to select the type hash field |
| 419 | // from an interface's descriptor word (whether a *runtime._type or |
| 420 | // *runtime.itab pointer). |
| 421 | func typeHashFieldOf(pos src.XPos, itab *ir.UnaryExpr) *ir.SelectorExpr { |
| 422 | if itab.Op() != ir.OITAB { |
| 423 | base.Fatalf("expected OITAB, got %v", itab.Op()) |
| 424 | } |
| 425 | var hashField *types.Field |
| 426 | if itab.X.Type().IsEmptyInterface() { |
| 427 | // runtime._type's hash field |
| 428 | if rtypeHashField == nil { |
| 429 | rtypeHashField = runtimeField("hash", int64(2*types.PtrSize), types.Types[types.TUINT32]) |
| 430 | } |
| 431 | hashField = rtypeHashField |
| 432 | } else { |
| 433 | // runtime.itab's hash field |
| 434 | if itabHashField == nil { |
| 435 | itabHashField = runtimeField("hash", int64(2*types.PtrSize), types.Types[types.TUINT32]) |
| 436 | } |
| 437 | hashField = itabHashField |
| 438 | } |
| 439 | return boundedDotPtr(pos, itab, hashField) |
| 440 | } |
| 441 | |
| 442 | var rtypeHashField, itabHashField *types.Field |
| 443 | |
| 444 | // A typeSwitch walks a type switch. |
| 445 | type typeSwitch struct { |
| 446 | // Temporary variables (i.e., ONAMEs) used by type switch dispatch logic: |
| 447 | facename ir.Node // value being type-switched on |
| 448 | hashname ir.Node // type hash of the value being type-switched on |
| 449 | okname ir.Node // boolean used for comma-ok type assertions |
| 450 | |
| 451 | done ir.Nodes |
| 452 | clauses []typeClause |
| 453 | } |
| 454 | |
| 455 | type typeClause struct { |
| 456 | hash uint32 |
| 457 | body ir.Nodes |
| 458 | } |
| 459 | |
Dan Willemsen | bc60c3c | 2021-12-15 01:09:00 -0800 | [diff] [blame] | 460 | func (s *typeSwitch) Add(pos src.XPos, n1 ir.Node, caseVar *ir.Name, jmp ir.Node) { |
| 461 | typ := n1.Type() |
Dan Willemsen | cc753b7 | 2021-08-31 13:25:42 -0700 | [diff] [blame] | 462 | var body ir.Nodes |
| 463 | if caseVar != nil { |
| 464 | l := []ir.Node{ |
| 465 | ir.NewDecl(pos, ir.ODCL, caseVar), |
| 466 | ir.NewAssignStmt(pos, caseVar, nil), |
| 467 | } |
| 468 | typecheck.Stmts(l) |
| 469 | body.Append(l...) |
| 470 | } else { |
| 471 | caseVar = ir.BlankNode.(*ir.Name) |
| 472 | } |
| 473 | |
| 474 | // cv, ok = iface.(type) |
| 475 | as := ir.NewAssignListStmt(pos, ir.OAS2, nil, nil) |
| 476 | as.Lhs = []ir.Node{caseVar, s.okname} // cv, ok = |
Dan Willemsen | bc60c3c | 2021-12-15 01:09:00 -0800 | [diff] [blame] | 477 | switch n1.Op() { |
| 478 | case ir.OTYPE: |
| 479 | // Static type assertion (non-generic) |
| 480 | dot := ir.NewTypeAssertExpr(pos, s.facename, nil) |
| 481 | dot.SetType(typ) // iface.(type) |
| 482 | as.Rhs = []ir.Node{dot} |
| 483 | case ir.ODYNAMICTYPE: |
| 484 | // Dynamic type assertion (generic) |
| 485 | dt := n1.(*ir.DynamicType) |
| 486 | dot := ir.NewDynamicTypeAssertExpr(pos, ir.ODYNAMICDOTTYPE, s.facename, dt.X) |
| 487 | if dt.ITab != nil { |
| 488 | dot.T = dt.ITab |
| 489 | } |
| 490 | dot.SetType(typ) |
| 491 | dot.SetTypecheck(1) |
| 492 | as.Rhs = []ir.Node{dot} |
| 493 | default: |
| 494 | base.Fatalf("unhandled type case %s", n1.Op()) |
| 495 | } |
Dan Willemsen | cc753b7 | 2021-08-31 13:25:42 -0700 | [diff] [blame] | 496 | appendWalkStmt(&body, as) |
| 497 | |
| 498 | // if ok { goto label } |
| 499 | nif := ir.NewIfStmt(pos, nil, nil, nil) |
| 500 | nif.Cond = s.okname |
| 501 | nif.Body = []ir.Node{jmp} |
| 502 | body.Append(nif) |
| 503 | |
Dan Willemsen | bc60c3c | 2021-12-15 01:09:00 -0800 | [diff] [blame] | 504 | if n1.Op() == ir.OTYPE && !typ.IsInterface() { |
| 505 | // Defer static, noninterface cases so they can be binary searched by hash. |
Dan Willemsen | cc753b7 | 2021-08-31 13:25:42 -0700 | [diff] [blame] | 506 | s.clauses = append(s.clauses, typeClause{ |
Dan Willemsen | bc60c3c | 2021-12-15 01:09:00 -0800 | [diff] [blame] | 507 | hash: types.TypeHash(n1.Type()), |
Dan Willemsen | cc753b7 | 2021-08-31 13:25:42 -0700 | [diff] [blame] | 508 | body: body, |
| 509 | }) |
| 510 | return |
| 511 | } |
| 512 | |
| 513 | s.flush() |
| 514 | s.done.Append(body.Take()...) |
| 515 | } |
| 516 | |
| 517 | func (s *typeSwitch) Emit(out *ir.Nodes) { |
| 518 | s.flush() |
| 519 | out.Append(s.done.Take()...) |
| 520 | } |
| 521 | |
| 522 | func (s *typeSwitch) flush() { |
| 523 | cc := s.clauses |
| 524 | s.clauses = nil |
| 525 | if len(cc) == 0 { |
| 526 | return |
| 527 | } |
| 528 | |
| 529 | sort.Slice(cc, func(i, j int) bool { return cc[i].hash < cc[j].hash }) |
| 530 | |
| 531 | // Combine adjacent cases with the same hash. |
| 532 | merged := cc[:1] |
| 533 | for _, c := range cc[1:] { |
| 534 | last := &merged[len(merged)-1] |
| 535 | if last.hash == c.hash { |
| 536 | last.body.Append(c.body.Take()...) |
| 537 | } else { |
| 538 | merged = append(merged, c) |
| 539 | } |
| 540 | } |
| 541 | cc = merged |
| 542 | |
| 543 | binarySearch(len(cc), &s.done, |
| 544 | func(i int) ir.Node { |
| 545 | return ir.NewBinaryExpr(base.Pos, ir.OLE, s.hashname, ir.NewInt(int64(cc[i-1].hash))) |
| 546 | }, |
| 547 | func(i int, nif *ir.IfStmt) { |
| 548 | // TODO(mdempsky): Omit hash equality check if |
| 549 | // there's only one type. |
| 550 | c := cc[i] |
| 551 | nif.Cond = ir.NewBinaryExpr(base.Pos, ir.OEQ, s.hashname, ir.NewInt(int64(c.hash))) |
| 552 | nif.Body.Append(c.body.Take()...) |
| 553 | }, |
| 554 | ) |
| 555 | } |
| 556 | |
| 557 | // binarySearch constructs a binary search tree for handling n cases, |
| 558 | // and appends it to out. It's used for efficiently implementing |
| 559 | // switch statements. |
| 560 | // |
| 561 | // less(i) should return a boolean expression. If it evaluates true, |
| 562 | // then cases before i will be tested; otherwise, cases i and later. |
| 563 | // |
| 564 | // leaf(i, nif) should setup nif (an OIF node) to test case i. In |
| 565 | // particular, it should set nif.Left and nif.Nbody. |
| 566 | func binarySearch(n int, out *ir.Nodes, less func(i int) ir.Node, leaf func(i int, nif *ir.IfStmt)) { |
| 567 | const binarySearchMin = 4 // minimum number of cases for binary search |
| 568 | |
| 569 | var do func(lo, hi int, out *ir.Nodes) |
| 570 | do = func(lo, hi int, out *ir.Nodes) { |
| 571 | n := hi - lo |
| 572 | if n < binarySearchMin { |
| 573 | for i := lo; i < hi; i++ { |
| 574 | nif := ir.NewIfStmt(base.Pos, nil, nil, nil) |
| 575 | leaf(i, nif) |
| 576 | base.Pos = base.Pos.WithNotStmt() |
| 577 | nif.Cond = typecheck.Expr(nif.Cond) |
| 578 | nif.Cond = typecheck.DefaultLit(nif.Cond, nil) |
| 579 | out.Append(nif) |
| 580 | out = &nif.Else |
| 581 | } |
| 582 | return |
| 583 | } |
| 584 | |
| 585 | half := lo + n/2 |
| 586 | nif := ir.NewIfStmt(base.Pos, nil, nil, nil) |
| 587 | nif.Cond = less(half) |
| 588 | base.Pos = base.Pos.WithNotStmt() |
| 589 | nif.Cond = typecheck.Expr(nif.Cond) |
| 590 | nif.Cond = typecheck.DefaultLit(nif.Cond, nil) |
| 591 | do(lo, half, &nif.Body) |
| 592 | do(half, hi, &nif.Else) |
| 593 | out.Append(nif) |
| 594 | } |
| 595 | |
| 596 | do(0, n, out) |
| 597 | } |