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go/test/escape_param.go
David Chase 7fbb1b36c3 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>
2015-05-01 13:47:20 +00:00

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// 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 escape
var sink interface{}
// in -> out
func param0(p *int) *int { // ERROR "leaking param: p to result ~r1"
return p
}
func caller0a() {
i := 0
_ = param0(&i) // ERROR "caller0a &i does not escape$"
}
func caller0b() {
i := 0 // ERROR "moved to heap: i$"
sink = param0(&i) // ERROR "&i escapes to heap$" "param0\(&i\) escapes to heap"
}
// in, in -> out, out
func param1(p1, p2 *int) (*int, *int) { // ERROR "leaking param: p1 to result ~r2" "leaking param: p2 to result ~r3"
return p1, p2
}
func caller1() {
i := 0 // ERROR "moved to heap: i$"
j := 0
sink, _ = param1(&i, &j) // ERROR "&i escapes to heap$" "caller1 &j does not escape$"
}
// in -> other in
func param2(p1 *int, p2 **int) { // ERROR "leaking param: p1$" "param2 p2 does not escape$"
*p2 = p1
}
func caller2a() {
i := 0 // ERROR "moved to heap: i$"
var p *int
param2(&i, &p) // ERROR "&i escapes to heap$" "caller2a &p does not escape$"
_ = p
}
func caller2b() {
i := 0 // ERROR "moved to heap: i$"
var p *int
param2(&i, &p) // ERROR "&i escapes to heap$" "caller2b &p does not escape$"
sink = p // ERROR "p escapes to heap$"
}
// in -> in
type Pair struct {
p1 *int
p2 *int
}
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$"
param3(&p) // ERROR "caller3a &p does not escape"
_ = p
}
func caller3b() {
i := 0 // ERROR "moved to heap: i$"
j := 0 // ERROR "moved to heap: j$"
p := Pair{&i, &j} // ERROR "&i escapes to heap$" "&j escapes to heap$"
param3(&p) // ERROR "caller3b &p does not escape"
sink = p // ERROR "p escapes to heap$"
}
// in -> rcvr
func (p *Pair) param4(i *int) { // ERROR "\(\*Pair\).param4 p does not escape$" "leaking param: i$"
p.p1 = i
}
func caller4a() {
i := 0 // ERROR "moved to heap: i$"
p := Pair{}
p.param4(&i) // ERROR "&i escapes to heap$" "caller4a p does not escape$"
_ = p
}
func caller4b() {
i := 0 // ERROR "moved to heap: i$"
p := Pair{}
p.param4(&i) // ERROR "&i escapes to heap$" "caller4b p does not escape$"
sink = p // ERROR "p escapes to heap$"
}
// in -> heap
func param5(i *int) { // ERROR "leaking param: i$"
sink = i // ERROR "i escapes to heap$"
}
func caller5() {
i := 0 // ERROR "moved to heap: i$"
param5(&i) // ERROR "&i escapes to heap$"
}
// *in -> heap
func param6(i ***int) { // ERROR "leaking param content: i$"
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$"
param6(&p2) // ERROR "caller6a &p2 does not escape"
}
// **in -> heap
func param7(i ***int) { // ERROR "leaking param content: i$"
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$"
p2 := &p // ERROR "&p escapes to heap$"
param7(&p2) // ERROR "caller7 &p2 does not escape"
}
// **in -> heap
func param8(i **int) { // ERROR "param8 i does not escape$"
sink = **i // ERROR "\* \(\*i\) escapes to heap"
}
func caller8() {
i := 0
p := &i // ERROR "caller8 &i does not escape$"
param8(&p) // ERROR "caller8 &p does not escape$"
}
// *in -> out
func param9(p ***int) **int { // ERROR "leaking param: p to result ~r1 level=1"
return *p
}
func caller9a() {
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$"
}
func caller9b() {
i := 0 // ERROR "moved to heap: i$"
p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
p2 := &p // ERROR "&p escapes to heap$"
sink = param9(&p2) // ERROR "caller9b &p2 does not escape$" "param9\(&p2\) escapes to heap"
}
// **in -> out
func param10(p ***int) *int { // ERROR "leaking param: p to result ~r1 level=2"
return **p
}
func caller10a() {
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$"
p2 := &p // ERROR "caller10b &p does not escape$"
sink = param10(&p2) // ERROR "caller10b &p2 does not escape$" "param10\(&p2\) escapes to heap"
}
// 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 "moved to heap: p" "&i escapes to heap"
_ = param11(&p) // ERROR "&p escapes to heap"
}
func caller11b() {
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"
}
func caller11c() { // GOOD
i := 0 // ERROR "moved to heap: i$"
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
type Indir struct {
p ***int
}
func (r *Indir) param12(i **int) { // ERROR "\(\*Indir\).param12 r does not escape$" "moved to heap: i$"
r.p = &i // ERROR "&i escapes to heap$"
}
func caller12a() {
i := 0 // ERROR "moved to heap: i$"
p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
var r Indir
r.param12(&p) // ERROR "&p escapes to heap$" "caller12a r does not escape$"
_ = r
}
func caller12b() {
i := 0 // ERROR "moved to heap: i$"
p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
r := &Indir{} // ERROR "caller12b &Indir literal does not escape$"
r.param12(&p) // ERROR "&p escapes to heap$"
_ = r
}
func caller12c() {
i := 0 // ERROR "moved to heap: i$"
p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
r := Indir{}
r.param12(&p) // ERROR "&p escapes to heap$" "caller12c r does not escape$"
sink = r // ERROR "r escapes to heap$"
}
func caller12d() {
i := 0 // ERROR "moved to heap: i$"
p := &i // ERROR "&i escapes to heap$" "moved to heap: p$"
r := Indir{}
r.param12(&p) // ERROR "&p escapes to heap$" "caller12d r does not escape$"
sink = **r.p // ERROR "\* \(\*r\.p\) escapes to heap"
}
// in -> value rcvr
type Val struct {
p **int
}
func (v Val) param13(i *int) { // ERROR "Val.param13 v does not escape$" "leaking param: i$"
*v.p = i
}
func caller13a() {
i := 0 // ERROR "moved to heap: i$"
var p *int
var v Val
v.p = &p // ERROR "caller13a &p does not escape$"
v.param13(&i) // ERROR "&i escapes to heap$"
_ = v
}
func caller13b() {
i := 0 // ERROR "moved to heap: i$"
var p *int
v := Val{&p} // ERROR "caller13b &p does not escape$"
v.param13(&i) // ERROR "&i escapes to heap$"
_ = v
}
func caller13c() {
i := 0 // ERROR "moved to heap: i$"
var p *int
v := &Val{&p} // ERROR "caller13c &Val literal does not escape$" "caller13c &p does not escape$"
v.param13(&i) // ERROR "&i escapes to heap$"
_ = v
}
func caller13d() {
i := 0 // ERROR "moved to heap: i$"
var p *int // ERROR "moved to heap: p$"
var v Val
v.p = &p // ERROR "&p escapes to heap$"
v.param13(&i) // ERROR "&i escapes to heap$"
sink = v // ERROR "v escapes to heap$"
}
func caller13e() {
i := 0 // ERROR "moved to heap: i$"
var p *int // ERROR "moved to heap: p$"
v := Val{&p} // ERROR "&p escapes to heap$"
v.param13(&i) // ERROR "&i escapes to heap$"
sink = v // ERROR "v escapes to heap$"
}
func caller13f() {
i := 0 // ERROR "moved to heap: i$"
var p *int // ERROR "moved to heap: p$"
v := &Val{&p} // ERROR "&Val literal escapes to heap$" "&p escapes to heap$"
v.param13(&i) // ERROR "&i escapes to heap$"
sink = v // ERROR "v escapes to heap$"
}
func caller13g() {
i := 0 // ERROR "moved to heap: i$"
var p *int
v := Val{&p} // ERROR "caller13g &p does not escape$"
v.param13(&i) // ERROR "&i escapes to heap$"
sink = *v.p // ERROR "\*v\.p escapes to heap"
}
func caller13h() {
i := 0 // ERROR "moved to heap: i$"
var p *int
v := &Val{&p} // ERROR "caller13h &Val literal does not escape$" "caller13h &p does not escape$"
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)
}
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