walk.go

Documentation: cmd/compile/internal/walk

     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  	"fmt"
     9  
    10  	"cmd/compile/internal/base"
    11  	"cmd/compile/internal/ir"
    12  	"cmd/compile/internal/reflectdata"
    13  	"cmd/compile/internal/ssagen"
    14  	"cmd/compile/internal/typecheck"
    15  	"cmd/compile/internal/types"
    16  	"cmd/internal/src"
    17  )
    18  
    19  // The constant is known to runtime.
    20  const tmpstringbufsize = 32
    21  
    22  func Walk(fn *ir.Func) {
    23  	ir.CurFunc = fn
    24  	errorsBefore := base.Errors()
    25  	order(fn)
    26  	if base.Errors() > errorsBefore {
    27  		return
    28  	}
    29  
    30  	if base.Flag.W != 0 {
    31  		s := fmt.Sprintf("\nbefore walk %v", ir.CurFunc.Sym())
    32  		ir.DumpList(s, ir.CurFunc.Body)
    33  	}
    34  
    35  	lno := base.Pos
    36  
    37  	base.Pos = lno
    38  	if base.Errors() > errorsBefore {
    39  		return
    40  	}
    41  	walkStmtList(ir.CurFunc.Body)
    42  	if base.Flag.W != 0 {
    43  		s := fmt.Sprintf("after walk %v", ir.CurFunc.Sym())
    44  		ir.DumpList(s, ir.CurFunc.Body)
    45  	}
    46  
    47  	// Eagerly compute sizes of all variables for SSA.
    48  	for _, n := range fn.Dcl {
    49  		types.CalcSize(n.Type())
    50  	}
    51  }
    52  
    53  // walkRecv walks an ORECV node.
    54  func walkRecv(n *ir.UnaryExpr) ir.Node {
    55  	if n.Typecheck() == 0 {
    56  		base.Fatalf("missing typecheck: %+v", n)
    57  	}
    58  	init := ir.TakeInit(n)
    59  
    60  	n.X = walkExpr(n.X, &init)
    61  	call := walkExpr(mkcall1(chanfn("chanrecv1", 2, n.X.Type()), nil, &init, n.X, typecheck.NodNil()), &init)
    62  	return ir.InitExpr(init, call)
    63  }
    64  
    65  func convas(n *ir.AssignStmt, init *ir.Nodes) *ir.AssignStmt {
    66  	if n.Op() != ir.OAS {
    67  		base.Fatalf("convas: not OAS %v", n.Op())
    68  	}
    69  	n.SetTypecheck(1)
    70  
    71  	if n.X == nil || n.Y == nil {
    72  		return n
    73  	}
    74  
    75  	lt := n.X.Type()
    76  	rt := n.Y.Type()
    77  	if lt == nil || rt == nil {
    78  		return n
    79  	}
    80  
    81  	if ir.IsBlank(n.X) {
    82  		n.Y = typecheck.DefaultLit(n.Y, nil)
    83  		return n
    84  	}
    85  
    86  	if !types.Identical(lt, rt) {
    87  		n.Y = typecheck.AssignConv(n.Y, lt, "assignment")
    88  		n.Y = walkExpr(n.Y, init)
    89  	}
    90  	types.CalcSize(n.Y.Type())
    91  
    92  	return n
    93  }
    94  
    95  func vmkcall(fn ir.Node, t *types.Type, init *ir.Nodes, va []ir.Node) *ir.CallExpr {
    96  	if init == nil {
    97  		base.Fatalf("mkcall with nil init: %v", fn)
    98  	}
    99  	if fn.Type() == nil || fn.Type().Kind() != types.TFUNC {
   100  		base.Fatalf("mkcall %v %v", fn, fn.Type())
   101  	}
   102  
   103  	n := fn.Type().NumParams()
   104  	if n != len(va) {
   105  		base.Fatalf("vmkcall %v needs %v args got %v", fn, n, len(va))
   106  	}
   107  
   108  	call := typecheck.Call(base.Pos, fn, va, false).(*ir.CallExpr)
   109  	call.SetType(t)
   110  	return walkExpr(call, init).(*ir.CallExpr)
   111  }
   112  
   113  func mkcall(name string, t *types.Type, init *ir.Nodes, args ...ir.Node) *ir.CallExpr {
   114  	return vmkcall(typecheck.LookupRuntime(name), t, init, args)
   115  }
   116  
   117  func mkcallstmt(name string, args ...ir.Node) ir.Node {
   118  	return mkcallstmt1(typecheck.LookupRuntime(name), args...)
   119  }
   120  
   121  func mkcall1(fn ir.Node, t *types.Type, init *ir.Nodes, args ...ir.Node) *ir.CallExpr {
   122  	return vmkcall(fn, t, init, args)
   123  }
   124  
   125  func mkcallstmt1(fn ir.Node, args ...ir.Node) ir.Node {
   126  	var init ir.Nodes
   127  	n := vmkcall(fn, nil, &init, args)
   128  	if len(init) == 0 {
   129  		return n
   130  	}
   131  	init.Append(n)
   132  	return ir.NewBlockStmt(n.Pos(), init)
   133  }
   134  
   135  func chanfn(name string, n int, t *types.Type) ir.Node {
   136  	if !t.IsChan() {
   137  		base.Fatalf("chanfn %v", t)
   138  	}
   139  	switch n {
   140  	case 1:
   141  		return typecheck.LookupRuntime(name, t.Elem())
   142  	case 2:
   143  		return typecheck.LookupRuntime(name, t.Elem(), t.Elem())
   144  	}
   145  	base.Fatalf("chanfn %d", n)
   146  	return nil
   147  }
   148  
   149  func mapfn(name string, t *types.Type, isfat bool) ir.Node {
   150  	if !t.IsMap() {
   151  		base.Fatalf("mapfn %v", t)
   152  	}
   153  	if mapfast(t) == mapslow || isfat {
   154  		return typecheck.LookupRuntime(name, t.Key(), t.Elem(), t.Key(), t.Elem())
   155  	}
   156  	return typecheck.LookupRuntime(name, t.Key(), t.Elem(), t.Elem())
   157  }
   158  
   159  func mapfndel(name string, t *types.Type) ir.Node {
   160  	if !t.IsMap() {
   161  		base.Fatalf("mapfn %v", t)
   162  	}
   163  	if mapfast(t) == mapslow {
   164  		return typecheck.LookupRuntime(name, t.Key(), t.Elem(), t.Key())
   165  	}
   166  	return typecheck.LookupRuntime(name, t.Key(), t.Elem())
   167  }
   168  
   169  const (
   170  	mapslow = iota
   171  	mapfast32
   172  	mapfast32ptr
   173  	mapfast64
   174  	mapfast64ptr
   175  	mapfaststr
   176  	nmapfast
   177  )
   178  
   179  type mapnames [nmapfast]string
   180  
   181  func mkmapnames(base string, ptr string) mapnames {
   182  	return mapnames{base, base + "_fast32", base + "_fast32" + ptr, base + "_fast64", base + "_fast64" + ptr, base + "_faststr"}
   183  }
   184  
   185  var mapaccess1 = mkmapnames("mapaccess1", "")
   186  var mapaccess2 = mkmapnames("mapaccess2", "")
   187  var mapassign = mkmapnames("mapassign", "ptr")
   188  var mapdelete = mkmapnames("mapdelete", "")
   189  
   190  func mapfast(t *types.Type) int {
   191  	// Check runtime/map.go:maxElemSize before changing.
   192  	if t.Elem().Size() > 128 {
   193  		return mapslow
   194  	}
   195  	switch reflectdata.AlgType(t.Key()) {
   196  	case types.AMEM32:
   197  		if !t.Key().HasPointers() {
   198  			return mapfast32
   199  		}
   200  		if types.PtrSize == 4 {
   201  			return mapfast32ptr
   202  		}
   203  		base.Fatalf("small pointer %v", t.Key())
   204  	case types.AMEM64:
   205  		if !t.Key().HasPointers() {
   206  			return mapfast64
   207  		}
   208  		if types.PtrSize == 8 {
   209  			return mapfast64ptr
   210  		}
   211  		// Two-word object, at least one of which is a pointer.
   212  		// Use the slow path.
   213  	case types.ASTRING:
   214  		return mapfaststr
   215  	}
   216  	return mapslow
   217  }
   218  
   219  func walkAppendArgs(n *ir.CallExpr, init *ir.Nodes) {
   220  	walkExprListSafe(n.Args, init)
   221  
   222  	// walkExprListSafe will leave OINDEX (s[n]) alone if both s
   223  	// and n are name or literal, but those may index the slice we're
   224  	// modifying here. Fix explicitly.
   225  	ls := n.Args
   226  	for i1, n1 := range ls {
   227  		ls[i1] = cheapExpr(n1, init)
   228  	}
   229  }
   230  
   231  // appendWalkStmt typechecks and walks stmt and then appends it to init.
   232  func appendWalkStmt(init *ir.Nodes, stmt ir.Node) {
   233  	op := stmt.Op()
   234  	n := typecheck.Stmt(stmt)
   235  	if op == ir.OAS || op == ir.OAS2 {
   236  		// If the assignment has side effects, walkExpr will append them
   237  		// directly to init for us, while walkStmt will wrap it in an OBLOCK.
   238  		// We need to append them directly.
   239  		// TODO(rsc): Clean this up.
   240  		n = walkExpr(n, init)
   241  	} else {
   242  		n = walkStmt(n)
   243  	}
   244  	init.Append(n)
   245  }
   246  
   247  // The max number of defers in a function using open-coded defers. We enforce this
   248  // limit because the deferBits bitmask is currently a single byte (to minimize code size)
   249  const maxOpenDefers = 8
   250  
   251  // backingArrayPtrLen extracts the pointer and length from a slice or string.
   252  // This constructs two nodes referring to n, so n must be a cheapExpr.
   253  func backingArrayPtrLen(n ir.Node) (ptr, length ir.Node) {
   254  	var init ir.Nodes
   255  	c := cheapExpr(n, &init)
   256  	if c != n || len(init) != 0 {
   257  		base.Fatalf("backingArrayPtrLen not cheap: %v", n)
   258  	}
   259  	ptr = ir.NewUnaryExpr(base.Pos, ir.OSPTR, n)
   260  	if n.Type().IsString() {
   261  		ptr.SetType(types.Types[types.TUINT8].PtrTo())
   262  	} else {
   263  		ptr.SetType(n.Type().Elem().PtrTo())
   264  	}
   265  	ptr.SetTypecheck(1)
   266  	length = ir.NewUnaryExpr(base.Pos, ir.OLEN, n)
   267  	length.SetType(types.Types[types.TINT])
   268  	length.SetTypecheck(1)
   269  	return ptr, length
   270  }
   271  
   272  // mayCall reports whether evaluating expression n may require
   273  // function calls, which could clobber function call arguments/results
   274  // currently on the stack.
   275  func mayCall(n ir.Node) bool {
   276  	// When instrumenting, any expression might require function calls.
   277  	if base.Flag.Cfg.Instrumenting {
   278  		return true
   279  	}
   280  
   281  	isSoftFloat := func(typ *types.Type) bool {
   282  		return types.IsFloat[typ.Kind()] || types.IsComplex[typ.Kind()]
   283  	}
   284  
   285  	return ir.Any(n, func(n ir.Node) bool {
   286  		// walk should have already moved any Init blocks off of
   287  		// expressions.
   288  		if len(n.Init()) != 0 {
   289  			base.FatalfAt(n.Pos(), "mayCall %+v", n)
   290  		}
   291  
   292  		switch n.Op() {
   293  		default:
   294  			base.FatalfAt(n.Pos(), "mayCall %+v", n)
   295  
   296  		case ir.OCALLFUNC, ir.OCALLINTER,
   297  			ir.OUNSAFEADD, ir.OUNSAFESLICE:
   298  			return true
   299  
   300  		case ir.OINDEX, ir.OSLICE, ir.OSLICEARR, ir.OSLICE3, ir.OSLICE3ARR, ir.OSLICESTR,
   301  			ir.ODEREF, ir.ODOTPTR, ir.ODOTTYPE, ir.ODYNAMICDOTTYPE, ir.ODIV, ir.OMOD,
   302  			ir.OSLICE2ARR, ir.OSLICE2ARRPTR:
   303  			// These ops might panic, make sure they are done
   304  			// before we start marshaling args for a call. See issue 16760.
   305  			return true
   306  
   307  		case ir.OANDAND, ir.OOROR:
   308  			n := n.(*ir.LogicalExpr)
   309  			// The RHS expression may have init statements that
   310  			// should only execute conditionally, and so cannot be
   311  			// pulled out to the top-level init list. We could try
   312  			// to be more precise here.
   313  			return len(n.Y.Init()) != 0
   314  
   315  		// When using soft-float, these ops might be rewritten to function calls
   316  		// so we ensure they are evaluated first.
   317  		case ir.OADD, ir.OSUB, ir.OMUL, ir.ONEG:
   318  			return ssagen.Arch.SoftFloat && isSoftFloat(n.Type())
   319  		case ir.OLT, ir.OEQ, ir.ONE, ir.OLE, ir.OGE, ir.OGT:
   320  			n := n.(*ir.BinaryExpr)
   321  			return ssagen.Arch.SoftFloat && isSoftFloat(n.X.Type())
   322  		case ir.OCONV:
   323  			n := n.(*ir.ConvExpr)
   324  			return ssagen.Arch.SoftFloat && (isSoftFloat(n.Type()) || isSoftFloat(n.X.Type()))
   325  
   326  		case ir.OMIN, ir.OMAX:
   327  			// string or float requires runtime call, see (*ssagen.state).minmax method.
   328  			return n.Type().IsString() || n.Type().IsFloat()
   329  
   330  		case ir.OLITERAL, ir.ONIL, ir.ONAME, ir.OLINKSYMOFFSET, ir.OMETHEXPR,
   331  			ir.OAND, ir.OANDNOT, ir.OLSH, ir.OOR, ir.ORSH, ir.OXOR, ir.OCOMPLEX, ir.OMAKEFACE,
   332  			ir.OADDR, ir.OBITNOT, ir.ONOT, ir.OPLUS,
   333  			ir.OCAP, ir.OIMAG, ir.OLEN, ir.OREAL,
   334  			ir.OCONVNOP, ir.ODOT,
   335  			ir.OCFUNC, ir.OIDATA, ir.OITAB, ir.OSPTR,
   336  			ir.OBYTES2STRTMP, ir.OGETG, ir.OGETCALLERPC, ir.OGETCALLERSP, ir.OSLICEHEADER, ir.OSTRINGHEADER:
   337  			// ok: operations that don't require function calls.
   338  			// Expand as needed.
   339  		}
   340  
   341  		return false
   342  	})
   343  }
   344  
   345  // itabType loads the _type field from a runtime.itab struct.
   346  func itabType(itab ir.Node) ir.Node {
   347  	if itabTypeField == nil {
   348  		// runtime.itab's _type field
   349  		itabTypeField = runtimeField("_type", int64(types.PtrSize), types.NewPtr(types.Types[types.TUINT8]))
   350  	}
   351  	return boundedDotPtr(base.Pos, itab, itabTypeField)
   352  }
   353  
   354  var itabTypeField *types.Field
   355  
   356  // boundedDotPtr returns a selector expression representing ptr.field
   357  // and omits nil-pointer checks for ptr.
   358  func boundedDotPtr(pos src.XPos, ptr ir.Node, field *types.Field) *ir.SelectorExpr {
   359  	sel := ir.NewSelectorExpr(pos, ir.ODOTPTR, ptr, field.Sym)
   360  	sel.Selection = field
   361  	sel.SetType(field.Type)
   362  	sel.SetTypecheck(1)
   363  	sel.SetBounded(true) // guaranteed not to fault
   364  	return sel
   365  }
   366  
   367  func runtimeField(name string, offset int64, typ *types.Type) *types.Field {
   368  	f := types.NewField(src.NoXPos, ir.Pkgs.Runtime.Lookup(name), typ)
   369  	f.Offset = offset
   370  	return f
   371  }
   372  
   373  // ifaceData loads the data field from an interface.
   374  // The concrete type must be known to have type t.
   375  // It follows the pointer if !IsDirectIface(t).
   376  func ifaceData(pos src.XPos, n ir.Node, t *types.Type) ir.Node {
   377  	if t.IsInterface() {
   378  		base.Fatalf("ifaceData interface: %v", t)
   379  	}
   380  	ptr := ir.NewUnaryExpr(pos, ir.OIDATA, n)
   381  	if types.IsDirectIface(t) {
   382  		ptr.SetType(t)
   383  		ptr.SetTypecheck(1)
   384  		return ptr
   385  	}
   386  	ptr.SetType(types.NewPtr(t))
   387  	ptr.SetTypecheck(1)
   388  	ind := ir.NewStarExpr(pos, ptr)
   389  	ind.SetType(t)
   390  	ind.SetTypecheck(1)
   391  	ind.SetBounded(true)
   392  	return ind
   393  }
   394
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