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cmd/gc: fix infinite loop in nil check removal
Fixes #8076. LGTM=iant R=golang-codereviews, iant CC=golang-codereviews https://golang.org/cl/93610043
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@ -956,7 +956,7 @@ nilwalkback(NilFlow *rcheck)
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static void
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nilwalkfwd(NilFlow *rcheck)
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{
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NilFlow *r;
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NilFlow *r, *last;
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Prog *p;
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ProgInfo info;
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@ -967,6 +967,7 @@ nilwalkfwd(NilFlow *rcheck)
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// avoid problems like:
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// _ = *x // should panic
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// for {} // no writes but infinite loop may be considered visible
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last = nil;
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for(r = (NilFlow*)uniqs(&rcheck->f); r != nil; r = (NilFlow*)uniqs(&r->f)) {
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p = r->f.prog;
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proginfo(&info, p);
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@ -989,5 +990,12 @@ nilwalkfwd(NilFlow *rcheck)
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// Stop if memory write.
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if((info.flags & RightWrite) && !regtyp(&p->to))
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return;
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// Stop if we jump backward.
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// This test is valid because all the NilFlow* are pointers into
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// a single contiguous array. We will need to add an explicit
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// numbering when the code is converted to Go.
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if(last != nil && r <= last)
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return;
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last = r;
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}
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}
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17
test/fixedbugs/issue8076.go
Normal file
17
test/fixedbugs/issue8076.go
Normal file
@ -0,0 +1,17 @@
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// compile
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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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// Issue 8076. nilwalkfwd walked forward forever
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// on the instruction loop following the dereference.
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package main
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func main() {
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_ = *(*int)(nil)
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L:
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_ = 0
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goto L
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}
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