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cmd/compile: fix evaluation of "" < s
Fixes #24817 Change-Id: Ifa79ab3dfe69297eeef85f7193cd5f85e5982bc5 Reviewed-on: https://go-review.googlesource.com/106655 Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Matthew Dempsky <mdempsky@google.com>
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@ -1275,6 +1275,13 @@ opswitch:
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}
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if cs != nil {
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cmp := n.SubOp()
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// Our comparison below assumes that the non-constant string
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// is on the left hand side, so rewrite "" cmp x to x cmp "".
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// See issue 24817.
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if Isconst(n.Left, CTSTR) {
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cmp = brrev(cmp)
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}
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// maxRewriteLen was chosen empirically.
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// It is the value that minimizes cmd/go file size
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// across most architectures.
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64
test/fixedbugs/issue24817.go
Normal file
64
test/fixedbugs/issue24817.go
Normal file
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@ -0,0 +1,64 @@
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// run
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// Copyright 2018 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 all ways to compare a non-constant string to the empty string.
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package main
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import (
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"fmt"
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"os"
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)
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var (
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s = "abc"
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e = ""
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failed bool
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)
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func main() {
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want(true, "" < s, `"" < s`)
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want(false, s < "", `s < ""`)
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want(false, "" < e, `"" < e`)
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want(false, e < "", `e < ""`)
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want(true, "" <= s, `"" <= s`)
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want(false, s <= "", `s <= ""`)
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want(true, "" <= e, `"" <= e`)
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want(true, e <= "", `e <= ""`)
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want(false, "" > s, `"" > s`)
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want(true, s > "", `s > ""`)
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want(false, "" > e, `"" > e`)
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want(false, e > "", `e > ""`)
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want(false, "" >= s, `"" >= s`)
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want(true, s >= "", `s >= ""`)
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want(true, "" >= e, `"" >= e`)
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want(true, e >= "", `e >= ""`)
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want(false, "" == s, `"" == s`)
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want(false, s == "", `s == ""`)
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want(true, "" == e, `"" == e`)
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want(true, e == "", `e == ""`)
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want(true, "" != s, `"" != s`)
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want(true, s != "", `s != ""`)
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want(false, "" != e, `"" != e`)
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want(false, e != "", `e != ""`)
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if failed {
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os.Exit(1)
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}
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}
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//go:noinline
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func want(b bool, have bool, msg string) {
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if b != have {
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fmt.Println(msg)
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failed = true
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}
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}
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