1 files changed, 472 insertions, 0 deletions
diff --git a/src/cmd/compile/internal/gc/esc.go b/src/cmd/compile/internal/gc/esc.go
new file mode 100644
index 0000000..6f328ab
--- /dev/null
+++ b/src/cmd/compile/internal/gc/esc.go
@@ -0,0 +1,472 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gc
+
+import (
+	"cmd/compile/internal/types"
+	"fmt"
+)
+
+func escapes(all []*Node) {
+	visitBottomUp(all, escapeFuncs)
+}
+
+const (
+	EscFuncUnknown = 0 + iota
+	EscFuncPlanned
+	EscFuncStarted
+	EscFuncTagged
+)
+
+func min8(a, b int8) int8 {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func max8(a, b int8) int8 {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+const (
+	EscUnknown = iota
+	EscNone    // Does not escape to heap, result, or parameters.
+	EscHeap    // Reachable from the heap
+	EscNever   // By construction will not escape.
+)
+
+// funcSym returns fn.Func.Nname.Sym if no nils are encountered along the way.
+func funcSym(fn *Node) *types.Sym {
+	if fn == nil || fn.Func.Nname == nil {
+		return nil
+	}
+	return fn.Func.Nname.Sym
+}
+
+// Mark labels that have no backjumps to them as not increasing e.loopdepth.
+// Walk hasn't generated (goto|label).Left.Sym.Label yet, so we'll cheat
+// and set it to one of the following two. Then in esc we'll clear it again.
+var (
+	looping    Node
+	nonlooping Node
+)
+
+func isSliceSelfAssign(dst, src *Node) bool {
+	// Detect the following special case.
+	//
+	//	func (b *Buffer) Foo() {
+	//		n, m := ...
+	//		b.buf = b.buf[n:m]
+	//	}
+	//
+	// This assignment is a no-op for escape analysis,
+	// it does not store any new pointers into b that were not already there.
+	// However, without this special case b will escape, because we assign to OIND/ODOTPTR.
+	// Here we assume that the statement will not contain calls,
+	// that is, that order will move any calls to init.
+	// Otherwise base ONAME value could change between the moments
+	// when we evaluate it for dst and for src.
+
+	// dst is ONAME dereference.
+	if dst.Op != ODEREF && dst.Op != ODOTPTR || dst.Left.Op != ONAME {
+		return false
+	}
+	// src is a slice operation.
+	switch src.Op {
+	case OSLICE, OSLICE3, OSLICESTR:
+		// OK.
+	case OSLICEARR, OSLICE3ARR:
+		// Since arrays are embedded into containing object,
+		// slice of non-pointer array will introduce a new pointer into b that was not already there
+		// (pointer to b itself). After such assignment, if b contents escape,
+		// b escapes as well. If we ignore such OSLICEARR, we will conclude
+		// that b does not escape when b contents do.
+		//
+		// Pointer to an array is OK since it's not stored inside b directly.
+		// For slicing an array (not pointer to array), there is an implicit OADDR.
+		// We check that to determine non-pointer array slicing.
+		if src.Left.Op == OADDR {
+			return false
+		}
+	default:
+		return false
+	}
+	// slice is applied to ONAME dereference.
+	if src.Left.Op != ODEREF && src.Left.Op != ODOTPTR || src.Left.Left.Op != ONAME {
+		return false
+	}
+	// dst and src reference the same base ONAME.
+	return dst.Left == src.Left.Left
+}
+
+// isSelfAssign reports whether assignment from src to dst can
+// be ignored by the escape analysis as it's effectively a self-assignment.
+func isSelfAssign(dst, src *Node) bool {
+	if isSliceSelfAssign(dst, src) {
+		return true
+	}
+
+	// Detect trivial assignments that assign back to the same object.
+	//
+	// It covers these cases:
+	//	val.x = val.y
+	//	val.x[i] = val.y[j]
+	//	val.x1.x2 = val.x1.y2
+	//	... etc
+	//
+	// These assignments do not change assigned object lifetime.
+
+	if dst == nil || src == nil || dst.Op != src.Op {
+		return false
+	}
+
+	switch dst.Op {
+	case ODOT, ODOTPTR:
+		// Safe trailing accessors that are permitted to differ.
+	case OINDEX:
+		if mayAffectMemory(dst.Right) || mayAffectMemory(src.Right) {
+			return false
+		}
+	default:
+		return false
+	}
+
+	// The expression prefix must be both "safe" and identical.
+	return samesafeexpr(dst.Left, src.Left)
+}
+
+// mayAffectMemory reports whether evaluation of n may affect the program's
+// memory state. If the expression can't affect memory state, then it can be
+// safely ignored by the escape analysis.
+func mayAffectMemory(n *Node) bool {
+	// We may want to use a list of "memory safe" ops instead of generally
+	// "side-effect free", which would include all calls and other ops that can
+	// allocate or change global state. For now, it's safer to start with the latter.
+	//
+	// We're ignoring things like division by zero, index out of range,
+	// and nil pointer dereference here.
+	switch n.Op {
+	case ONAME, OCLOSUREVAR, OLITERAL:
+		return false
+
+	// Left+Right group.
+	case OINDEX, OADD, OSUB, OOR, OXOR, OMUL, OLSH, ORSH, OAND, OANDNOT, ODIV, OMOD:
+		return mayAffectMemory(n.Left) || mayAffectMemory(n.Right)
+
+	// Left group.
+	case ODOT, ODOTPTR, ODEREF, OCONVNOP, OCONV, OLEN, OCAP,
+		ONOT, OBITNOT, OPLUS, ONEG, OALIGNOF, OOFFSETOF, OSIZEOF:
+		return mayAffectMemory(n.Left)
+
+	default:
+		return true
+	}
+}
+
+// heapAllocReason returns the reason the given Node must be heap
+// allocated, or the empty string if it doesn't.
+func heapAllocReason(n *Node) string {
+	if n.Type == nil {
+		return ""
+	}
+
+	// Parameters are always passed via the stack.
+	if n.Op == ONAME && (n.Class() == PPARAM || n.Class() == PPARAMOUT) {
+		return ""
+	}
+
+	if n.Type.Width > maxStackVarSize {
+		return "too large for stack"
+	}
+
+	if (n.Op == ONEW || n.Op == OPTRLIT) && n.Type.Elem().Width >= maxImplicitStackVarSize {
+		return "too large for stack"
+	}
+
+	if n.Op == OCLOSURE && closureType(n).Size() >= maxImplicitStackVarSize {
+		return "too large for stack"
+	}
+	if n.Op == OCALLPART && partialCallType(n).Size() >= maxImplicitStackVarSize {
+		return "too large for stack"
+	}
+
+	if n.Op == OMAKESLICE {
+		r := n.Right
+		if r == nil {
+			r = n.Left
+		}
+		if !smallintconst(r) {
+			return "non-constant size"
+		}
+		if t := n.Type; t.Elem().Width != 0 && r.Int64Val() >= maxImplicitStackVarSize/t.Elem().Width {
+			return "too large for stack"
+		}
+	}
+
+	return ""
+}
+
+// addrescapes tags node n as having had its address taken
+// by "increasing" the "value" of n.Esc to EscHeap.
+// Storage is allocated as necessary to allow the address
+// to be taken.
+func addrescapes(n *Node) {
+	switch n.Op {
+	default:
+		// Unexpected Op, probably due to a previous type error. Ignore.
+
+	case ODEREF, ODOTPTR:
+		// Nothing to do.
+
+	case ONAME:
+		if n == nodfp {
+			break
+		}
+
+		// if this is a tmpname (PAUTO), it was tagged by tmpname as not escaping.
+		// on PPARAM it means something different.
+		if n.Class() == PAUTO && n.Esc == EscNever {
+			break
+		}
+
+		// If a closure reference escapes, mark the outer variable as escaping.
+		if n.Name.IsClosureVar() {
+			addrescapes(n.Name.Defn)
+			break
+		}
+
+		if n.Class() != PPARAM && n.Class() != PPARAMOUT && n.Class() != PAUTO {
+			break
+		}
+
+		// This is a plain parameter or local variable that needs to move to the heap,
+		// but possibly for the function outside the one we're compiling.
+		// That is, if we have:
+		//
+		//	func f(x int) {
+		//		func() {
+		//			global = &x
+		//		}
+		//	}
+		//
+		// then we're analyzing the inner closure but we need to move x to the
+		// heap in f, not in the inner closure. Flip over to f before calling moveToHeap.
+		oldfn := Curfn
+		Curfn = n.Name.Curfn
+		if Curfn.Func.Closure != nil && Curfn.Op == OCLOSURE {
+			Curfn = Curfn.Func.Closure
+		}
+		ln := lineno
+		lineno = Curfn.Pos
+		moveToHeap(n)
+		Curfn = oldfn
+		lineno = ln
+
+	// ODOTPTR has already been introduced,
+	// so these are the non-pointer ODOT and OINDEX.
+	// In &x[0], if x is a slice, then x does not
+	// escape--the pointer inside x does, but that
+	// is always a heap pointer anyway.
+	case ODOT, OINDEX, OPAREN, OCONVNOP:
+		if !n.Left.Type.IsSlice() {
+			addrescapes(n.Left)
+		}
+	}
+}
+
+// moveToHeap records the parameter or local variable n as moved to the heap.
+func moveToHeap(n *Node) {
+	if Debug.r != 0 {
+		Dump("MOVE", n)
+	}
+	if compiling_runtime {
+		yyerror("%v escapes to heap, not allowed in runtime", n)
+	}
+	if n.Class() == PAUTOHEAP {
+		Dump("n", n)
+		Fatalf("double move to heap")
+	}
+
+	// Allocate a local stack variable to hold the pointer to the heap copy.
+	// temp will add it to the function declaration list automatically.
+	heapaddr := temp(types.NewPtr(n.Type))
+	heapaddr.Sym = lookup("&" + n.Sym.Name)
+	heapaddr.Orig.Sym = heapaddr.Sym
+	heapaddr.Pos = n.Pos
+
+	// Unset AutoTemp to persist the &foo variable name through SSA to
+	// liveness analysis.
+	// TODO(mdempsky/drchase): Cleaner solution?
+	heapaddr.Name.SetAutoTemp(false)
+
+	// Parameters have a local stack copy used at function start/end
+	// in addition to the copy in the heap that may live longer than
+	// the function.
+	if n.Class() == PPARAM || n.Class() == PPARAMOUT {
+		if n.Xoffset == BADWIDTH {
+			Fatalf("addrescapes before param assignment")
+		}
+
+		// We rewrite n below to be a heap variable (indirection of heapaddr).
+		// Preserve a copy so we can still write code referring to the original,
+		// and substitute that copy into the function declaration list
+		// so that analyses of the local (on-stack) variables use it.
+		stackcopy := newname(n.Sym)
+		stackcopy.Type = n.Type
+		stackcopy.Xoffset = n.Xoffset
+		stackcopy.SetClass(n.Class())
+		stackcopy.Name.Param.Heapaddr = heapaddr
+		if n.Class() == PPARAMOUT {
+			// Make sure the pointer to the heap copy is kept live throughout the function.
+			// The function could panic at any point, and then a defer could recover.
+			// Thus, we need the pointer to the heap copy always available so the
+			// post-deferreturn code can copy the return value back to the stack.
+			// See issue 16095.
+			heapaddr.Name.SetIsOutputParamHeapAddr(true)
+		}
+		n.Name.Param.Stackcopy = stackcopy
+
+		// Substitute the stackcopy into the function variable list so that
+		// liveness and other analyses use the underlying stack slot
+		// and not the now-pseudo-variable n.
+		found := false
+		for i, d := range Curfn.Func.Dcl {
+			if d == n {
+				Curfn.Func.Dcl[i] = stackcopy
+				found = true
+				break
+			}
+			// Parameters are before locals, so can stop early.
+			// This limits the search even in functions with many local variables.
+			if d.Class() == PAUTO {
+				break
+			}
+		}
+		if !found {
+			Fatalf("cannot find %v in local variable list", n)
+		}
+		Curfn.Func.Dcl = append(Curfn.Func.Dcl, n)
+	}
+
+	// Modify n in place so that uses of n now mean indirection of the heapaddr.
+	n.SetClass(PAUTOHEAP)
+	n.Xoffset = 0
+	n.Name.Param.Heapaddr = heapaddr
+	n.Esc = EscHeap
+	if Debug.m != 0 {
+		Warnl(n.Pos, "moved to heap: %v", n)
+	}
+}
+
+// This special tag is applied to uintptr variables
+// that we believe may hold unsafe.Pointers for
+// calls into assembly functions.
+const unsafeUintptrTag = "unsafe-uintptr"
+
+// This special tag is applied to uintptr parameters of functions
+// marked go:uintptrescapes.
+const uintptrEscapesTag = "uintptr-escapes"
+
+func (e *Escape) paramTag(fn *Node, narg int, f *types.Field) string {
+	name := func() string {
+		if f.Sym != nil {
+			return f.Sym.Name
+		}
+		return fmt.Sprintf("arg#%d", narg)
+	}
+
+	if fn.Nbody.Len() == 0 {
+		// Assume that uintptr arguments must be held live across the call.
+		// This is most important for syscall.Syscall.
+		// See golang.org/issue/13372.
+		// This really doesn't have much to do with escape analysis per se,
+		// but we are reusing the ability to annotate an individual function
+		// argument and pass those annotations along to importing code.
+		if f.Type.IsUintptr() {
+			if Debug.m != 0 {
+				Warnl(f.Pos, "assuming %v is unsafe uintptr", name())
+			}
+			return unsafeUintptrTag
+		}
+
+		if !f.Type.HasPointers() { // don't bother tagging for scalars
+			return ""
+		}
+
+		var esc EscLeaks
+
+		// External functions are assumed unsafe, unless
+		// //go:noescape is given before the declaration.
+		if fn.Func.Pragma&Noescape != 0 {
+			if Debug.m != 0 && f.Sym != nil {
+				Warnl(f.Pos, "%v does not escape", name())
+			}
+		} else {
+			if Debug.m != 0 && f.Sym != nil {
+				Warnl(f.Pos, "leaking param: %v", name())
+			}
+			esc.AddHeap(0)
+		}
+
+		return esc.Encode()
+	}
+
+	if fn.Func.Pragma&UintptrEscapes != 0 {
+		if f.Type.IsUintptr() {
+			if Debug.m != 0 {
+				Warnl(f.Pos, "marking %v as escaping uintptr", name())
+			}
+			return uintptrEscapesTag
+		}
+		if f.IsDDD() && f.Type.Elem().IsUintptr() {
+			// final argument is ...uintptr.
+			if Debug.m != 0 {
+				Warnl(f.Pos, "marking %v as escaping ...uintptr", name())
+			}
+			return uintptrEscapesTag
+		}
+	}
+
+	if !f.Type.HasPointers() { // don't bother tagging for scalars
+		return ""
+	}
+
+	// Unnamed parameters are unused and therefore do not escape.
+	if f.Sym == nil || f.Sym.IsBlank() {
+		var esc EscLeaks
+		return esc.Encode()
+	}
+
+	n := asNode(f.Nname)
+	loc := e.oldLoc(n)
+	esc := loc.paramEsc
+	esc.Optimize()
+
+	if Debug.m != 0 && !loc.escapes {
+		if esc.Empty() {
+			Warnl(f.Pos, "%v does not escape", name())
+		}
+		if x := esc.Heap(); x >= 0 {
+			if x == 0 {
+				Warnl(f.Pos, "leaking param: %v", name())
+			} else {
+				// TODO(mdempsky): Mention level=x like below?
+				Warnl(f.Pos, "leaking param content: %v", name())
+			}
+		}
+		for i := 0; i < numEscResults; i++ {
+			if x := esc.Result(i); x >= 0 {
+				res := fn.Type.Results().Field(i).Sym
+				Warnl(f.Pos, "leaking param: %v to result %v level=%d", name(), res, x)
+			}
+		}
+	}
+
+	return esc.Encode()
+}