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![David Chase](/assets/img/avatar_default.png)
Adds: GOEXPERIMENT=loopvar (expected way of invoking) -d=loopvar={-1,0,1,2,11,12} (for per-package control and/or logging) -d=loopvarhash=... (for hash debugging) loopvar=11,12 are for testing, benchmarking, and debugging. If enabled,for loops of the form `for x,y := range thing`, if x and/or y are addressed or captured by a closure, are transformed by renaming x/y to a temporary and prepending an assignment to the body of the loop x := tmp_x. This changes the loop semantics by making each iteration's instance of x be distinct from the others (currently they are all aliased, and when this matters, it is almost always a bug). 3-range with captured iteration variables are also transformed, though it is a more complex transformation. "Optimized" to do a simpler transformation for 3-clause for where the increment is empty. (Prior optimization of address-taking under Return disabled, because it was incorrect; returns can have loops for children. Restored in a later CL.) Includes support for -d=loopvarhash=<binary string> intended for use with hash search and GOCOMPILEDEBUG=loopvarhash=<binary string> (use `gossahash -e loopvarhash command-that-fails`). Minor feature upgrades to hash-triggered features; clients can specify that file-position hashes use only the most-inline position, and/or that they use only the basenames of source files (not the full directory path). Most-inlined is the right choice for debugging loop-iteration change once the semantics are linked to the package across inlining; basename-only makes it tractable to write tests (which, otherwise, depend on the full pathname of the source file and thus vary). Updates #57969. Change-Id: I180a51a3f8d4173f6210c861f10de23de8a1b1db Reviewed-on: https://go-review.googlesource.com/c/go/+/411904 Reviewed-by: Matthew Dempsky <mdempsky@google.com> Run-TryBot: David Chase <drchase@google.com> TryBot-Result: Gopher Robot <gobot@golang.org>
134 lines
1.9 KiB
Go
134 lines
1.9 KiB
Go
// run
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// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Check that these do not use "by value" capturing,
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// because changes are made to the value during the closure.
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package main
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var never bool
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func main() {
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{
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type X struct {
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v int
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}
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var x X
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func() {
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x.v++
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}()
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if x.v != 1 {
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panic("x.v != 1")
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}
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type Y struct {
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X
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}
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var y Y
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func() {
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y.v = 1
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}()
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if y.v != 1 {
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panic("y.v != 1")
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}
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}
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{
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type Z struct {
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a [3]byte
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}
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var z Z
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func() {
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i := 0
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for z.a[1] = 1; i < 10; i++ {
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}
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}()
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if z.a[1] != 1 {
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panic("z.a[1] != 1")
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}
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}
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{
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w := 0
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tmp := 0
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f := func() {
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if w != 1 {
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panic("w != 1")
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}
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}
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func() {
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tmp = w // force capture of w, but do not write to it yet
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_ = tmp
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func() {
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func() {
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w++ // write in a nested closure
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}()
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}()
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}()
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f()
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}
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{
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var g func() int
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var i int
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for i = range [2]int{} {
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if i == 0 {
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g = func() int {
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return i // test that we capture by ref here, i is mutated on every interaction
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}
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}
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}
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if g() != 1 {
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panic("g() != 1")
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}
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}
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{
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var g func() int
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q := 0
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for range [2]int{} {
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q++
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g = func() int {
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return q // test that we capture by ref here
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// q++ must on a different decldepth than q declaration
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}
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}
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if g() != 2 {
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panic("g() != 2")
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}
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}
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{
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var g func() int
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var a [2]int
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q := 0
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for a[func() int {
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q++
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return 0
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}()] = range [2]int{} {
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g = func() int {
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return q // test that we capture by ref here
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// q++ must on a different decldepth than q declaration
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}
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}
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if g() != 2 {
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panic("g() != 2")
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}
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}
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{
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var g func() int
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q := 0
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q, g = 1, func() int { return q }
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if never {
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g = func() int { return 2 }
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}
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if g() != 1 {
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panic("g() != 1")
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}
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}
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}
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