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cmd/compile: preserve loop depth when evaluating block

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Add block method to preserve loop depth when evaluating statements in a
block, so escape analysis can handle looping label more precisely.

Updates #22438

Change-Id: I39b306544a6c0ee3fcbebbe0d0ee735cb71773e6
Reviewed-on: https://go-review.googlesource.com/c/go/+/193517
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Cuong Manh Le 2019-09-05 11:15:59 +07:00 committed by Matthew Dempsky
parent c99598cbd3
commit 1406ece446
2 changed files with 58 additions and 8 deletions
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22
src/cmd/compile/internal/gc/escape.go
View File

@ -201,7 +201,7 @@ func (e *Escape) walkFunc(fn *Node) {
e.curfn = fn e.curfn = fn
e.loopDepth = 1 e.loopDepth = 1
e.stmts(fn.Nbody) e.block(fn.Nbody)
} }
// Below we implement the methods for walking the AST and recording // Below we implement the methods for walking the AST and recording
@ -284,14 +284,14 @@ func (e *Escape) stmt(n *Node) {
case OIF: case OIF:
e.discard(n.Left) e.discard(n.Left)
e.stmts(n.Nbody) e.block(n.Nbody)
e.stmts(n.Rlist) e.block(n.Rlist)
case OFOR, OFORUNTIL: case OFOR, OFORUNTIL:
e.loopDepth++ e.loopDepth++
e.discard(n.Left) e.discard(n.Left)
e.stmt(n.Right) e.stmt(n.Right)
e.stmts(n.Nbody) e.block(n.Nbody)
e.loopDepth-- e.loopDepth--
case ORANGE: case ORANGE:
@ -311,7 +311,7 @@ func (e *Escape) stmt(n *Node) {
} }
} }
e.stmts(n.Nbody) e.block(n.Nbody)
e.loopDepth-- e.loopDepth--
case OSWITCH: case OSWITCH:
@ -340,13 +340,13 @@ func (e *Escape) stmt(n *Node) {
} }
e.discards(cas.List) e.discards(cas.List)
e.stmts(cas.Nbody) e.block(cas.Nbody)
} }
case OSELECT: case OSELECT:
for _, cas := range n.List.Slice() { for _, cas := range n.List.Slice() {
e.stmt(cas.Left) e.stmt(cas.Left)
e.stmts(cas.Nbody) e.block(cas.Nbody)
} }
case OSELRECV: case OSELRECV:
e.assign(n.Left, n.Right, "selrecv", n) e.assign(n.Left, n.Right, "selrecv", n)
@ -398,12 +398,18 @@ func (e *Escape) stmt(n *Node) {
} }
func (e *Escape) stmts(l Nodes) { func (e *Escape) stmts(l Nodes) {
// TODO(mdempsky): Preserve and restore e.loopDepth? See also #22438.
for _, n := range l.Slice() { for _, n := range l.Slice() {
e.stmt(n) e.stmt(n)
} }
} }
// block is like stmts, but preserves loopDepth.
func (e *Escape) block(l Nodes) {
old := e.loopDepth
e.stmts(l)
e.loopDepth = old
}
// expr models evaluating an expression n and flowing the result into // expr models evaluating an expression n and flowing the result into
// hole k. // hole k.
func (e *Escape) expr(k EscHole, n *Node) { func (e *Escape) expr(k EscHole, n *Node) {

44
test/escape_goto.go Normal file
View File

@ -0,0 +1,44 @@
// errorcheck -0 -m -l
// Copyright 2019 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 goto statements.
package escape
var x bool
func _() {
var p *int
loop:
if x {
goto loop
}
// BAD: We should be able to recognize that there
// aren't any more "goto loop" after here.
p = new(int) // ERROR "escapes to heap"
_ = p
}
func _() {
var p *int
if x {
loop:
goto loop
} else {
p = new(int) // ERROR "does not escape"
}
_ = p
}
func _() {
var p *int
if x {
loop:
goto loop
}
p = new(int) // ERROR "does not escape"
_ = p
}