mirror of
https://github.com/golang/go
synced 2024-10-06 08:00:07 +00:00
b700cb4974
The new channel and map runtime routines take pointers
to values, typically temporaries. Without help, the compiler
cannot tell when those temporaries stop being needed,
because it isn't sure what happened to the pointer.
Arrange to insert explicit VARKILL instructions for these
temporaries so that the liveness analysis can avoid seeing
them as "ambiguously live".
The change is made in order.c, which was already in charge of
introducing temporaries to preserve the order-of-evaluation
guarantees. Now its job has expanded to include introducing
temporaries as needed by runtime routines, and then also
inserting the VARKILL annotations for all these temporaries,
so that their lifetimes can be shortened.
In order to do its job for the map runtime routines, order.c arranges
that all map lookups or map assignments have the form:
x = m[k]
x, y = m[k]
m[k] = x
where x, y, and k are simple variables (often temporaries).
Likewise, receiving from a channel is now always:
x = <-c
In order to provide the map guarantee, order.c is responsible for
rewriting x op= y into x = x op y, so that m[k] += z becomes
t = m[k]
t2 = t + z
m[k] = t2
While here, fix a few bugs in order.c's traversal: it was failing to
walk into select and switch case bodies, so order of evaluation
guarantees were not preserved in those situations.
Added tests to test/reorder2.go.
Fixes #7671.
In gc/popt's temporary-merging optimization, allow merging
of temporaries with their address taken as long as the liveness
ranges do not intersect. (There is a good chance of that now
that we have VARKILL annotations to limit the liveness range.)
Explicitly killing temporaries cuts the number of ambiguously
live temporaries that must be zeroed in the godoc binary from
860 to 711, or -17%. There is more work to be done, but this
is a good checkpoint.
Update #7345
LGTM=khr
R=khr
CC=golang-codereviews
https://golang.org/cl/81940043
333 lines
8.3 KiB
Go
333 lines
8.3 KiB
Go
// errorcheck -0 -l -live
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// Copyright 2014 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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package main
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func f1() {
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var x *int
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print(&x) // ERROR "live at call to printpointer: x$"
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print(&x) // ERROR "live at call to printpointer: x$"
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}
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func f2(b bool) {
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if b {
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print(0) // nothing live here
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return
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}
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var x *int
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print(&x) // ERROR "live at call to printpointer: x$"
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print(&x) // ERROR "live at call to printpointer: x$"
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}
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func f3(b bool) {
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print(0)
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if b == false {
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print(0) // nothing live here
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return
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}
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if b {
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var x *int
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print(&x) // ERROR "live at call to printpointer: x$"
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print(&x) // ERROR "live at call to printpointer: x$"
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} else {
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var y *int
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print(&y) // ERROR "live at call to printpointer: y$"
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print(&y) // ERROR "live at call to printpointer: y$"
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}
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print(0) // ERROR "live at call to printint: x y$" "x \(type \*int\) is ambiguously live" "y \(type \*int\) is ambiguously live"
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}
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// The old algorithm treated x as live on all code that
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// could flow to a return statement, so it included the
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// function entry and code above the declaration of x
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// but would not include an indirect use of x in an infinite loop.
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// Check that these cases are handled correctly.
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func f4(b1, b2 bool) { // x not live here
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if b2 {
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print(0) // x not live here
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return
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}
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var z **int
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x := new(int)
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*x = 42
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z = &x
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print(**z) // ERROR "live at call to printint: x z$"
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if b2 {
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print(1) // ERROR "live at call to printint: x$"
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return
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}
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for {
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print(**z) // ERROR "live at call to printint: x z$"
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}
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}
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func f5(b1 bool) {
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var z **int
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if b1 {
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x := new(int)
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*x = 42
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z = &x
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} else {
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y := new(int)
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*y = 54
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z = &y
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}
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print(**z) // ERROR "live at call to printint: x y$" "x \(type \*int\) is ambiguously live" "y \(type \*int\) is ambiguously live"
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}
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// confusion about the _ result used to cause spurious "live at entry to f6: _".
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func f6() (_, y string) {
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y = "hello"
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return
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}
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// confusion about addressed results used to cause "live at entry to f7: x".
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func f7() (x string) {
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_ = &x
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x = "hello"
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return
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}
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// ignoring block returns used to cause "live at entry to f8: x, y".
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func f8() (x, y string) {
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return g8()
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}
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func g8() (string, string)
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// ignoring block assignments used to cause "live at entry to f9: x"
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// issue 7205
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var i9 interface{}
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func f9() bool {
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g8()
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x := i9
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return x != 99
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}
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// liveness formerly confused by UNDEF followed by RET,
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// leading to "live at entry to f10: ~r1" (unnamed result).
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func f10() string {
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panic(1)
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}
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// liveness formerly confused by select, thinking runtime.selectgo
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// can return to next instruction; it always jumps elsewhere.
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// note that you have to use at least two cases in the select
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// to get a true select; smaller selects compile to optimized helper functions.
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var c chan *int
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var b bool
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// this used to have a spurious "live at entry to f11a: ~r0"
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func f11a() *int {
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select { // ERROR "live at call to selectgo: autotmp"
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case <-c: // ERROR "live at call to selectrecv: autotmp"
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return nil
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case <-c: // ERROR "live at call to selectrecv: autotmp"
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return nil
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}
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}
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func f11b() *int {
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p := new(int)
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if b {
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// At this point p is dead: the code here cannot
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// get to the bottom of the function.
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// This used to have a spurious "live at call to printint: p".
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print(1) // nothing live here!
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select { // ERROR "live at call to selectgo: autotmp"
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case <-c: // ERROR "live at call to selectrecv: autotmp"
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return nil
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case <-c: // ERROR "live at call to selectrecv: autotmp"
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return nil
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}
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}
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println(*p)
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return nil
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}
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func f11c() *int {
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p := new(int)
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if b {
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// Unlike previous, the cases in this select fall through,
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// so we can get to the println, so p is not dead.
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print(1) // ERROR "live at call to printint: p"
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select { // ERROR "live at call to newselect: p" "live at call to selectgo: autotmp.* p"
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case <-c: // ERROR "live at call to selectrecv: autotmp.* p"
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case <-c: // ERROR "live at call to selectrecv: autotmp.* p"
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}
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}
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println(*p)
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return nil
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}
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// similarly, select{} does not fall through.
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// this used to have a spurious "live at entry to f12: ~r0".
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func f12() *int {
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if b {
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select{}
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} else {
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return nil
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}
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}
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// incorrectly placed VARDEF annotations can cause missing liveness annotations.
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// this used to be missing the fact that s is live during the call to g13 (because it is
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// needed for the call to h13).
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func f13() {
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s := "hello"
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s = h13(s, g13(s)) // ERROR "live at call to g13: s"
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}
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func g13(string) string
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func h13(string, string) string
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// more incorrectly placed VARDEF.
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func f14() {
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x := g14()
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print(&x) // ERROR "live at call to printpointer: x"
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}
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func g14() string
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func f15() {
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var x string
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_ = &x
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x = g15() // ERROR "live at call to g15: x"
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print(x) // ERROR "live at call to printstring: x"
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}
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func g15() string
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// Checking that various temporaries do not persist or cause
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// ambiguously live values that must be zeroed.
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// The exact temporary names are inconsequential but we are
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// trying to check that there is only one at any given site,
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// and also that none show up in "ambiguously live" messages.
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var m map[string]int
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func f16() {
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if b {
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delete(m, "hi") // ERROR "live at call to mapdelete: autotmp_[0-9]+$"
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}
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delete(m, "hi") // ERROR "live at call to mapdelete: autotmp_[0-9]+$"
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delete(m, "hi") // ERROR "live at call to mapdelete: autotmp_[0-9]+$"
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}
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var m2s map[string]*byte
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var m2 map[[2]string]*byte
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var x2 [2]string
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var bp *byte
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func f17a() {
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// value temporary only
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if b {
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m2[x2] = nil // ERROR "live at call to mapassign1: autotmp_[0-9]+$"
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}
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m2[x2] = nil // ERROR "live at call to mapassign1: autotmp_[0-9]+$"
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m2[x2] = nil // ERROR "live at call to mapassign1: autotmp_[0-9]+$"
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}
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func f17b() {
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// key temporary only
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if b {
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m2s["x"] = bp // ERROR "live at call to mapassign1: autotmp_[0-9]+$"
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}
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m2s["x"] = bp // ERROR "live at call to mapassign1: autotmp_[0-9]+$"
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m2s["x"] = bp // ERROR "live at call to mapassign1: autotmp_[0-9]+$"
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}
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func f17c() {
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// key and value temporaries
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if b {
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m2s["x"] = nil // ERROR "live at call to mapassign1: autotmp_[0-9]+ autotmp_[0-9]+$"
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}
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m2s["x"] = nil // ERROR "live at call to mapassign1: autotmp_[0-9]+ autotmp_[0-9]+$"
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m2s["x"] = nil // ERROR "live at call to mapassign1: autotmp_[0-9]+ autotmp_[0-9]+$"
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}
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func g18() [2]string
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func f18() {
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// key temporary for mapaccess.
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// temporary introduced by orderexpr.
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var z *byte
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if b {
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z = m2[g18()] // ERROR "live at call to mapaccess1: autotmp_[0-9]+$"
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}
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z = m2[g18()] // ERROR "live at call to mapaccess1: autotmp_[0-9]+$"
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z = m2[g18()] // ERROR "live at call to mapaccess1: autotmp_[0-9]+$"
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print(z)
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}
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var ch chan *byte
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func f19() {
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// dest temporary for channel receive.
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var z *byte
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if b {
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z = <-ch // ERROR "live at call to chanrecv1: autotmp_[0-9]+$"
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}
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z = <-ch // ERROR "live at call to chanrecv1: autotmp_[0-9]+$"
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z = <-ch // ERROR "live at call to chanrecv1: autotmp_[0-9]+$"
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print(z)
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}
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func f20() {
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// src temporary for channel send
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if b {
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ch <- nil // ERROR "live at call to chansend1: autotmp_[0-9]+$"
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}
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ch <- nil // ERROR "live at call to chansend1: autotmp_[0-9]+$"
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ch <- nil // ERROR "live at call to chansend1: autotmp_[0-9]+$"
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}
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func f21() {
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// key temporary for mapaccess using array literal key.
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var z *byte
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if b {
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z = m2[[2]string{"x", "y"}] // ERROR "live at call to mapaccess1: autotmp_[0-9]+$"
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}
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z = m2[[2]string{"x", "y"}] // ERROR "live at call to mapaccess1: autotmp_[0-9]+$"
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z = m2[[2]string{"x", "y"}] // ERROR "live at call to mapaccess1: autotmp_[0-9]+$"
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print(z)
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}
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func f23() {
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// key temporary for two-result map access using array literal key.
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var z *byte
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var ok bool
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if b {
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z, ok = m2[[2]string{"x", "y"}] // ERROR "live at call to mapaccess2: autotmp_[0-9]+$"
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}
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z, ok = m2[[2]string{"x", "y"}] // ERROR "live at call to mapaccess2: autotmp_[0-9]+$"
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z, ok = m2[[2]string{"x", "y"}] // ERROR "live at call to mapaccess2: autotmp_[0-9]+$"
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print(z, ok)
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}
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func f24() {
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// key temporary for map access using array literal key.
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// value temporary too.
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if b {
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m2[[2]string{"x", "y"}] = nil // ERROR "live at call to mapassign1: autotmp_[0-9]+ autotmp_[0-9]+$"
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}
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m2[[2]string{"x", "y"}] = nil // ERROR "live at call to mapassign1: autotmp_[0-9]+ autotmp_[0-9]+$"
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m2[[2]string{"x", "y"}] = nil // ERROR "live at call to mapassign1: autotmp_[0-9]+ autotmp_[0-9]+$"
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}
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