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-rw-r--r--test/fixedbugs/issue41780.go39
1 files changed, 39 insertions, 0 deletions
diff --git a/test/fixedbugs/issue41780.go b/test/fixedbugs/issue41780.go
new file mode 100644
index 0000000..632c144
--- /dev/null
+++ b/test/fixedbugs/issue41780.go
@@ -0,0 +1,39 @@
+// run
+
+// Copyright 2020 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.
+
+// Checks that conversion of CMP(x,-y) -> CMN(x,y) is only applied in correct context.
+
+package main
+
+type decimal struct {
+ d [8]byte // digits, big-endian representation
+ dp int // decimal point
+}
+
+var powtab = []int{1, 3, 6, 9, 13, 16, 19, 23, 26}
+
+//go:noinline
+func foo(d *decimal) int {
+ exp := int(d.d[1])
+ if d.dp < 0 || d.dp == 0 && d.d[0] < '5' {
+ var n int
+ if -d.dp >= len(powtab) {
+ n = 27
+ } else {
+ n = powtab[-d.dp] // incorrect CMP -> CMN substitution causes indexing panic.
+ }
+ exp += n
+ }
+ return exp
+}
+
+func main() {
+ var d decimal
+ d.d[0] = '1'
+ if foo(&d) != 1 {
+ println("FAILURE (though not the one this test was written to catch)")
+ }
+}