cmd/internal/gc: improve flow of input params to output params

This includes the following information in the per-function summary:

outK = paramJ   encoded in outK bits for paramJ
outK = *paramJ  encoded in outK bits for paramJ
heap = paramJ   EscHeap
heap = *paramJ  EscContentEscapes

Note that (currently) if the address of a parameter is taken and
returned, necessarily a heap allocation occurred to contain that
reference, and the heap can never refer to stack, therefore the
parameter and everything downstream from it escapes to the heap.

The per-function summary information now has a tuneable number of bits
(2 is probably noticeably better than 1, 3 is likely overkill, but it
is now easy to check and the -m debugging output includes information
that allows you to figure out if more would be better.)

A new test was  added to check pointer flow through struct-typed and
*struct-typed parameters and returns; some of these are sensitive to
the number of summary bits, and ought to yield better results with a
more competent escape analysis algorithm.  Another new test checks
(some) correctness with array parameters, results, and operations.

The old analysis inferred a piece of plan9 runtime was non-escaping by
counteracting overconservative analysis with buggy analysis; with the
bug fixed, the result was too conservative (and it's not easy to fix
in this framework) so the source code was tweaked to get the desired
result.  A test was added against the discovered bug.

The escape analysis was further improved splitting the "level" into
3 parts, one tracking the conventional "level" and the other two
computing the highest-level-suffix-from-copy, which is used to
generally model the cancelling effect of indirection applied to
address-of.

With the improved escape analysis enabled, it was necessary to
modify one of the runtime tests because it now attempts to allocate
too much on the (small, fixed-size) G0 (system) stack and this
failed the test.

Compiling src/std after touching src/runtime/*.go with -m logging
turned on shows 420 fewer heap allocation sites (10538 vs 10968).

Profiling allocations in src/html/template with
for i in {1..5} ;
  do go tool 6g -memprofile=mastx.${i}.prof  -memprofilerate=1 *.go;
  go tool pprof -alloc_objects -text  mastx.${i}.prof ;
done

showed a 15% reduction in allocations performed by the compiler.

Update #3753
Update #4720
Fixes #10466

Change-Id: I0fd97d5f5ac527b45f49e2218d158a6e89951432
Reviewed-on: https://go-review.googlesource.com/8202
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/internal/gc/gen.go

@@ -23,11 +23,10 @@ func Sysfunc(name string) *Node {
 	return n
 }
 
-/*
- * the address of n has been taken and might be used after
- * the current function returns.  mark any local vars
- * as needing to move to the heap.
- */
+// 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 {
 	// probably a type error already.
@@ -98,7 +97,7 @@ func addrescapes(n *Node) {
 	// 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:
+	case ODOT, OINDEX, OPAREN, OCONVNOP:
 		if !Isslice(n.Left.Type) {
 			addrescapes(n.Left)
 		}

src/cmd/internal/gc/go.go

@@ -214,19 +214,6 @@ type InitPlan struct {
 	E    []InitEntry
 }
 
-const (
-	EscUnknown = iota
-	EscHeap
-	EscScope
-	EscNone
-	EscReturn
-	EscNever
-	EscBits           = 3
-	EscMask           = (1 << EscBits) - 1
-	EscContentEscapes = 1 << EscBits // value obtained by indirect of parameter escapes to some returned result
-	EscReturnBits     = EscBits + 1
-)
-
 const (
 	SymExport   = 1 << 0 // to be exported
 	SymPackage  = 1 << 1

src/cmd/internal/gc/syntax.go

@@ -52,7 +52,7 @@ type Node struct {
 	Likely      int8   // likeliness of if statement
 	Hasbreak    bool   // has break statement
 	Needzero    bool   // if it contains pointers, needs to be zeroed on function entry
-	Esc         uint8 // EscXXX
+	Esc         uint16 // EscXXX
 	Funcdepth   int32
 
 	// most nodes
@@ -103,14 +103,14 @@ type Node struct {
 	Escloopdepth int       // -1: global, 0: return variables, 1:function top level, increased inside function for every loop or label to mark scopes
 
 	Sym      *Sym  // various
-	Vargen   int32 // unique name for OTYPE/ONAME
+	Vargen   int32 // unique name for OTYPE/ONAME within a function.  Function outputs are numbered starting at one.
 	Lineno   int32
 	Xoffset  int64
 	Stkdelta int64 // offset added by stack frame compaction phase.
 	Ostk     int32 // 6g only
 	Iota     int32
 	Walkgen  uint32
-	Esclevel int32
+	Esclevel Level
 	Opt      interface{} // for optimization passes
 }
 

src/cmd/internal/gc/walk.go

@@ -1777,7 +1777,7 @@ func ascompatet(op int, nl *NodeList, nr **Type, fp int, init **NodeList) *NodeL
 * package all the arguments that match a ... T parameter into a []T.
  */
 func mkdotargslice(lr0 *NodeList, nn *NodeList, l *Type, fp int, init **NodeList, ddd *Node) *NodeList {
-	esc := uint8(EscUnknown)
+	esc := uint16(EscUnknown)
 	if ddd != nil {
 		esc = ddd.Esc
 	}

src/runtime/proc1.go

@@ -3531,9 +3531,13 @@ func testSchedLocalQueue() {
 	}
 }
 
+var pSink *p
+
 func testSchedLocalQueueSteal() {
 	p1 := new(p)
 	p2 := new(p)
+	pSink = p1 // Force to heap, too large to allocate on system stack ("G0 stack")
+	pSink = p2 // Force to heap, too large to allocate on system stack ("G0 stack")
 	gs := make([]g, len(p1.runq))
 	for i := 0; i < len(p1.runq); i++ {
 		for j := 0; j < i; j++ {

src/runtime/string1.go

@@ -35,10 +35,8 @@ var maxstring uintptr = 256 // a hint for print
 
 //go:nosplit
 func gostringnocopy(str *byte) string {
-	var s string
-	sp := (*stringStruct)(unsafe.Pointer(&s))
-	sp.str = unsafe.Pointer(str)
-	sp.len = findnull(str)
+	ss := stringStruct{str: unsafe.Pointer(str), len: findnull(str)}
+	s := *(*string)(unsafe.Pointer(&ss))
 	for {
 		ms := maxstring
 		if uintptr(len(s)) <= ms || casuintptr(&maxstring, ms, uintptr(len(s))) {

test/escape_array.go

+// errorcheck -0 -m -l
+
+// Copyright 2015 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.
+
+// Test escape analysis for function parameters.
+
+// In this test almost everything is BAD except the simplest cases
+// where input directly flows to output.
+
+package foo
+
+var Ssink *string
+
+type U [2]*string
+
+func bar(a, b *string) U { // ERROR "leaking param: a to result ~r2 level=0$" "leaking param: b to result ~r2 level=0$"
+	return U{a, b}
+}
+
+func foo(x U) U { // ERROR "leaking param: x to result ~r1 level=0$"
+	return U{x[1], x[0]}
+}
+
+func bff(a, b *string) U { // ERROR "leaking param: a to result ~r2 level=0$" "leaking param: b to result ~r2 level=0$"
+	return foo(foo(bar(a, b)))
+}
+
+func tbff1() *string {
+	a := "cat"
+	b := "dog"       // ERROR "moved to heap: b$"
+	u := bff(&a, &b) // ERROR "tbff1 &a does not escape$" "tbff1 &b does not escape$"
+	_ = u[0]
+	return &b // ERROR "&b escapes to heap$"
+}
+
+// BAD: need fine-grained analysis to track u[0] and u[1] differently.
+func tbff2() *string {
+	a := "cat"       // ERROR "moved to heap: a$"
+	b := "dog"       // ERROR "moved to heap: b$"
+	u := bff(&a, &b) // ERROR "&a escapes to heap$" "&b escapes to heap$"
+	_ = u[0]
+	return u[1]
+}
+
+func car(x U) *string { // ERROR "leaking param: x to result ~r1 level=0$"
+	return x[0]
+}
+
+// BAD: need fine-grained analysis to track x[0] and x[1] differently.
+func fun(x U, y *string) *string { // ERROR "leaking param: x to result ~r2 level=0$" "leaking param: y to result ~r2 level=0$"
+	x[0] = y
+	return x[1]
+}
+
+func fup(x *U, y *string) *string { // ERROR "leaking param: x to result ~r2 level=1$" "leaking param: y$"
+	x[0] = y // leaking y to heap is intended
+	return x[1]
+}
+
+// BAD: would be nice to record that *y (content) is what leaks, not y itself
+func fum(x *U, y **string) *string { // ERROR "leaking param: x to result ~r2 level=1$" "leaking param content: y$"
+	x[0] = *y
+	return x[1]
+}
+
+// BAD: would be nice to record that y[0] (content) is what leaks, not y itself
+func fuo(x *U, y *U) *string { // ERROR "leaking param: x to result ~r2 level=1$" "leaking param content: y$"
+	x[0] = y[0]
+	return x[1]
+}

test/escape_calls.go

+// errorcheck -0 -m -l
+
+// Copyright 2015 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.
+
+// Test escape analysis for function parameters.
+
+// In this test almost everything is BAD except the simplest cases
+// where input directly flows to output.
+
+package foo
+
+func f(buf []byte) []byte { // ERROR "leaking param: buf to result ~r1 level=0$"
+	return buf
+}
+
+func g(*byte) string
+
+func h(e int) {
+	var x [32]byte // ERROR "moved to heap: x$"
+	g(&f(x[:])[0]) // ERROR "&f\(x\[:\]\)\[0\] escapes to heap$" "x escapes to heap$"
+}
+
+type Node struct {
+	s           string
+	left, right *Node
+}
+
+func walk(np **Node) int { // ERROR "leaking param content: np"
+	n := *np
+	w := len(n.s)
+	if n == nil {
+		return 0
+	}
+	wl := walk(&n.left)  // ERROR "walk &n.left does not escape"
+	wr := walk(&n.right) // ERROR "walk &n.right does not escape"
+	if wl < wr {
+		n.left, n.right = n.right, n.left
+		wl, wr = wr, wl
+	}
+	*np = n
+	return w + wl + wr
+}

test/escape_closure.go

@@ -131,7 +131,7 @@ func ClosureCallArgs14() {
 	x := 0 // ERROR "moved to heap: x"
 	// BAD: &x should not escape here
 	p := &x                  // ERROR "moved to heap: p" "&x escapes to heap"
-	_ = func(p **int) *int { // ERROR "leaking param p content to result ~r1" "func literal does not escape"
+	_ = func(p **int) *int { // ERROR "leaking param: p to result ~r1 level=1" "func literal does not escape"
 		return *p
 		// BAD: p should not escape here
 	}(&p) // ERROR "&p escapes to heap"
@@ -140,7 +140,7 @@ func ClosureCallArgs14() {
 func ClosureCallArgs15() {
 	x := 0                      // ERROR "moved to heap: x"
 	p := &x                     // ERROR "moved to heap: p" "&x escapes to heap"
-	sink = func(p **int) *int { // ERROR "leaking param p content to result ~r1" "func literal does not escape"
+	sink = func(p **int) *int { // ERROR "leaking param: p to result ~r1 level=1" "func literal does not escape"
 		return *p
 		// BAD: p should not escape here
 	}(&p) // ERROR "&p escapes to heap" "\(func literal\)\(&p\) escapes to heap"

test/escape_field.go

@@ -59,17 +59,16 @@ func field5() {
 }
 
 // BAD: we are not leaking param x, only x.p2
-func field6(x *X) { // ERROR "leaking param: x$"
+func field6(x *X) { // ERROR "leaking param content: x$"
 	sink = x.p2 // ERROR "x\.p2 escapes to heap"
 }
 
 func field6a() {
 	i := 0 // ERROR "moved to heap: i$"
-	var x X // ERROR "moved to heap: x$"
+	var x X
 	// BAD: &i should not escape
 	x.p1 = &i  // ERROR "&i escapes to heap$"
-	// BAD: &x should not escape
-	field6(&x) // ERROR "&x escapes to heap$"
+	field6(&x) // ERROR "field6a &x does not escape"
 }
 
 func field7() {

test/escape_indir.go

@@ -61,7 +61,7 @@ func constptr2() {
 	i := 0           // ERROR "moved to heap: i"
 	x := &ConstPtr{} // ERROR "&ConstPtr literal does not escape"
 	x.p = &i         // ERROR "&i escapes to heap"
-	sink = *x// ERROR "\*x escapes to heap"
+	sink = *x        // ERROR "\*x escapes to heap"
 }
 
 func constptr4() *ConstPtr {
@@ -78,7 +78,7 @@ func constptr5() *ConstPtr {
 }
 
 // BAD: p should not escape here
-func constptr6(p *ConstPtr) { // ERROR "leaking param: p"
+func constptr6(p *ConstPtr) { // ERROR "leaking param content: p"
 	p1 := &ConstPtr{} // ERROR "&ConstPtr literal does not escape"
 	*p1 = *p
 	_ = p1
@@ -151,3 +151,10 @@ func foo2() {
 	i := 0  // ERROR "moved to heap: i"
 	*p = &i // ERROR "&i escapes to heap"
 }
+
+var global *byte
+
+func f() {
+	var x byte    // ERROR "moved to heap: x"
+	global = &*&x // ERROR "&\(\*\(&x\)\) escapes to heap" "&x escapes to heap"
+}

test/escape_level.go

@@ -68,9 +68,9 @@ func level6() {
 
 func level7() {
 	i := 0    // ERROR "moved to heap: i"
-	p0 := &i   // ERROR "moved to heap: p0" "&i escapes to heap"
-	// BAD: p0 should not escape here
-	p1 := &p0  // ERROR "&p0 escapes to heap"
+	p0 := &i  // ERROR "&i escapes to heap"
+	p1 := &p0 // ERROR "&p0 does not escape"
+	// note *p1 == &i
 	p2 := *p1  // ERROR "moved to heap: p2"
 	sink = &p2 // ERROR "&p2 escapes to heap"
 }

test/escape_param.go

@@ -14,7 +14,7 @@ package escape
 var sink interface{}
 
 // in -> out
-func param0(p *int) *int { // ERROR "leaking param: p to result ~r1$"
+func param0(p *int) *int { // ERROR "leaking param: p to result ~r1"
 	return p
 }
 
@@ -29,7 +29,7 @@ func caller0b() {
 }
 
 // in, in -> out, out
-func param1(p1, p2 *int) (*int, *int) { // ERROR "leaking param: p1 to result ~r2$" "leaking param: p2 to result ~r3$"
+func param1(p1, p2 *int) (*int, *int) { // ERROR "leaking param: p1 to result ~r2" "leaking param: p2 to result ~r3"
 	return p1, p2
 }
 
@@ -64,23 +64,23 @@ type Pair struct {
 	p2 *int
 }
 
-func param3(p *Pair) { // ERROR "leaking param: p$"
+func param3(p *Pair) { // ERROR "leaking param content: p$"
 	p.p1 = p.p2
 }
 
 func caller3a() {
 	i := 0            // ERROR "moved to heap: i$"
 	j := 0            // ERROR "moved to heap: j$"
-	p := Pair{&i, &j} // ERROR "&i escapes to heap$" "&j escapes to heap$" "moved to heap: p$"
-	param3(&p)        // ERROR "&p escapes to heap$"
+	p := Pair{&i, &j} // ERROR "&i escapes to heap$" "&j escapes to heap$"
+	param3(&p)        // ERROR "caller3a &p does not escape"
 	_ = p
 }
 
 func caller3b() {
 	i := 0            // ERROR "moved to heap: i$"
 	j := 0            // ERROR "moved to heap: j$"
-	p := Pair{&i, &j} // ERROR "&i escapes to heap$" "&j escapes to heap$" "moved to heap: p$"
-	param3(&p)        // ERROR "&p escapes to heap$"
+	p := Pair{&i, &j} // ERROR "&i escapes to heap$" "&j escapes to heap$"
+	param3(&p)        // ERROR "caller3b &p does not escape"
 	sink = p          // ERROR "p escapes to heap$"
 }
 
@@ -114,27 +114,27 @@ func caller5() {
 }
 
 // *in -> heap
-func param6(i ***int) { // ERROR "leaking param: i$"
+func param6(i ***int) { // ERROR "leaking param content: i$"
 	sink = *i // ERROR "\*i escapes to heap$"
 }
 
 func caller6a() {
 	i := 0      // ERROR "moved to heap: i$"
 	p := &i     // ERROR "&i escapes to heap$" "moved to heap: p$"
-	p2 := &p    // ERROR "&p escapes to heap$" "moved to heap: p2$"
-	param6(&p2) // ERROR "&p2 escapes to heap$"
+	p2 := &p    // ERROR "&p escapes to heap$"
+	param6(&p2) // ERROR "caller6a &p2 does not escape"
 }
 
 // **in -> heap
-func param7(i ***int) { // ERROR "leaking param: i$"
+func param7(i ***int) { // ERROR "leaking param content: i$"
 	sink = **i // ERROR "\* \(\*i\) escapes to heap"
 }
 
 func caller7() {
 	i := 0      // ERROR "moved to heap: i$"
 	p := &i     // ERROR "&i escapes to heap$" "moved to heap: p$"
-	p2 := &p    // ERROR "&p escapes to heap$" "moved to heap: p2$"
-	param7(&p2) // ERROR "&p2 escapes to heap$"
+	p2 := &p    // ERROR "&p escapes to heap$"
+	param7(&p2) // ERROR "caller7 &p2 does not escape"
 }
 
 // **in -> heap
@@ -149,14 +149,14 @@ func caller8() {
 }
 
 // *in -> out
-func param9(p ***int) **int { // ERROR "param9 leaking param p content to result ~r1$"
+func param9(p ***int) **int { // ERROR "leaking param: p to result ~r1 level=1"
 	return *p
 }
 
 func caller9a() {
-	i := 0          // ERROR "moved to heap: i$"
-	p := &i         // ERROR "&i escapes to heap$" "moved to heap: p$"
-	p2 := &p        // ERROR "&p escapes to heap$"
+	i := 0
+	p := &i         // ERROR "caller9a &i does not escape"
+	p2 := &p        // ERROR "caller9a &p does not escape"
 	_ = param9(&p2) // ERROR "caller9a &p2 does not escape$"
 }
 
@@ -168,33 +168,33 @@ func caller9b() {
 }
 
 // **in -> out
-func param10(p ***int) *int { // ERROR "param10 leaking param p content to result ~r1$"
+func param10(p ***int) *int { // ERROR "leaking param: p to result ~r1 level=2"
 	return **p
 }
 
 func caller10a() {
-	i := 0           // ERROR "moved to heap: i$"
-	p := &i          // ERROR "&i escapes to heap$" "moved to heap: p$"
-	p2 := &p         // ERROR "&p escapes to heap$"
+	i := 0
+	p := &i          // ERROR "caller10a &i does not escape"
+	p2 := &p         // ERROR "caller10a &p does not escape"
 	_ = param10(&p2) // ERROR "caller10a &p2 does not escape$"
 }
 
 func caller10b() {
 	i := 0              // ERROR "moved to heap: i$"
-	p := &i             // ERROR "&i escapes to heap$" "moved to heap: p$"
-	p2 := &p            // ERROR "&p escapes to heap$"
+	p := &i             // ERROR "&i escapes to heap$"
+	p2 := &p            // ERROR "caller10b &p does not escape$"
 	sink = param10(&p2) // ERROR "caller10b &p2 does not escape$" "param10\(&p2\) escapes to heap"
 }
 
-// &in -> out
+// in escapes to heap (address of param taken and returned)
 func param11(i **int) ***int { // ERROR "moved to heap: i$"
 	return &i // ERROR "&i escapes to heap$"
 }
 
 func caller11a() {
-	i := 0          // ERROR "moved to heap: i$"
-	p := &i         // ERROR "&i escapes to heap$" "moved to heap: p$"
-	_ = param11(&p) // ERROR "&p escapes to heap$"
+	i := 0          // ERROR "moved to heap: i"
+	p := &i         // ERROR "moved to heap: p" "&i escapes to heap"
+	_ = param11(&p) // ERROR "&p escapes to heap"
 }
 
 func caller11b() {
@@ -203,10 +203,17 @@ func caller11b() {
 	sink = param11(&p) // ERROR "&p escapes to heap$" "param11\(&p\) escapes to heap"
 }
 
-func caller11c() {
+func caller11c() { // GOOD
 	i := 0              // ERROR "moved to heap: i$"
-	p := &i             // ERROR "&i escapes to heap$" "moved to heap: p$"
-	sink = *param11(&p) // ERROR "&p escapes to heap$" "\*param11\(&p\) escapes to heap"
+	p := &i             // ERROR "moved to heap: p" "&i escapes to heap"
+	sink = *param11(&p) // ERROR "&p escapes to heap" "\*param11\(&p\) escapes to heap"
+}
+
+func caller11d() {
+	i := 0             // ERROR "moved to heap: i$"
+	p := &i            // ERROR "&i escapes to heap" "moved to heap: p"
+	p2 := &p           // ERROR "&p escapes to heap"
+	sink = param11(p2) // ERROR "param11\(p2\) escapes to heap"
 }
 
 // &in -> rcvr
@@ -324,3 +331,23 @@ func caller13h() {
 	v.param13(&i) // ERROR "&i escapes to heap$"
 	sink = **v.p  // ERROR "\* \(\*v\.p\) escapes to heap"
 }
+
+type Node struct {
+	p *Node
+}
+
+var Sink *Node
+
+func f(x *Node) { // ERROR "leaking param content: x"
+	Sink = &Node{x.p} // ERROR "&Node literal escapes to heap"
+}
+
+func g(x *Node) *Node { // ERROR "leaking param: x to result ~r1 level=0"
+	return &Node{x.p} // ERROR "&Node literal escapes to heap"
+}
+
+func h(x *Node) { // ERROR "leaking param: x"
+	y := &Node{x} // ERROR "h &Node literal does not escape"
+	Sink = g(y)
+	f(y)
+}

test/escape_struct_return.go

+// errorcheck -0 -m -l
+
+// Copyright 2015 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.
+
+// Test escape analysis for function parameters.
+
+package foo
+
+var Ssink *string
+
+type U struct {
+	_sp  *string
+	_spp **string
+}
+
+func A(sp *string, spp **string) U { // ERROR "leaking param: sp to result ~r2 level=0$" "leaking param: spp to result ~r2 level=0$"
+	return U{sp, spp}
+}
+
+func B(spp **string) U { // ERROR "leaking param: spp to result ~r1 level=0$" "leaking param: spp to result ~r1 level=1$"
+	return U{*spp, spp}
+}
+
+func tA1() {
+	s := "cat"
+	sp := &s   // ERROR "tA1 &s does not escape$"
+	spp := &sp // ERROR "tA1 &sp does not escape$"
+	u := A(sp, spp)
+	_ = u
+	println(s)
+}
+
+func tA2() {
+	s := "cat"
+	sp := &s   // ERROR "tA2 &s does not escape$"
+	spp := &sp // ERROR "tA2 &sp does not escape$"
+	u := A(sp, spp)
+	println(*u._sp)
+}
+
+func tA3() {
+	s := "cat"
+	sp := &s   // ERROR "tA3 &s does not escape$"
+	spp := &sp // ERROR "tA3 &sp does not escape$"
+	u := A(sp, spp)
+	println(**u._spp)
+}
+
+func tB1() {
+	s := "cat"
+	sp := &s   // ERROR "tB1 &s does not escape$"
+	spp := &sp // ERROR "tB1 &sp does not escape$"
+	u := B(spp)
+	_ = u
+	println(s)
+}
+
+func tB2() {
+	s := "cat"
+	sp := &s   // ERROR "tB2 &s does not escape$"
+	spp := &sp // ERROR "tB2 &sp does not escape$"
+	u := B(spp)
+	println(*u._sp)
+}
+
+func tB3() {
+	s := "cat"
+	sp := &s   // ERROR "tB3 &s does not escape$"
+	spp := &sp // ERROR "tB3 &sp does not escape$"
+	u := B(spp)
+	println(**u._spp)
+}

test/fixedbugs/issue10353.go

@@ -45,5 +45,5 @@ func growstack(x int) {
 	if x == 0 {
 		return
 	}
-	growstack(x-1)
+	growstack(x - 1)
 }