cmd/compile: don't constant fold divide by zero

It just makes the compiler crash. Oops.

Fixes #43099

Change-Id: Id996c14799c1a5d0063ecae3b8770568161c2440
Reviewed-on: https://go-review.googlesource.com/c/go/+/276652
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/test/fixedbugs/issue43099.go b/test/fixedbugs/issue43099.go
new file mode 100644
index 0000000000..16f18e5f96
--- /dev/null
+++ b/test/fixedbugs/issue43099.go
@@ -0,0 +1,34 @@
+// compile
+
+// 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.
+
+// Check to make sure we don't try to constant fold a divide by zero.
+// This is a tricky test, as we need a value that's not recognized as 0
+// until lowering (otherwise it gets handled in a different path).
+
+package p
+
+func f() {
+	var i int
+	var s string
+	for i > 0 {
+		_ = s[0]
+		i++
+	}
+
+	var c chan int
+	c <- 1 % i
+}
+
+func f32() uint32 {
+	s := "\x00\x00\x00\x00"
+	c := uint32(s[0]) | uint32(s[1])<<8 | uint32(s[2])<<16 | uint32(s[3])<<24
+	return 1 / c
+}
+func f64() uint64 {
+	s := "\x00\x00\x00\x00\x00\x00\x00\x00"
+	c := uint64(s[0]) | uint64(s[1])<<8 | uint64(s[2])<<16 | uint64(s[3])<<24 | uint64(s[4])<<32 | uint64(s[5])<<40 | uint64(s[6])<<48 | uint64(s[7])<<56
+	return 1 / c
+}