cmd/compile: fix simplification rules on arm/arm64

Fixes #48473

Change-Id: Ic1e918f916eae223a3b530a51a58f03031924670
Reviewed-on: https://go-review.googlesource.com/c/go/+/350913
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/test/fixedbugs/issue48473.go b/test/fixedbugs/issue48473.go
new file mode 100644
index 0000000000..8edef1f14f
--- /dev/null
+++ b/test/fixedbugs/issue48473.go
@@ -0,0 +1,30 @@
+// run
+
+// Copyright 2021 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.
+
+package main
+
+import "fmt"
+
+func f(x uint64) uint64 {
+	s := "\x04"
+	c := s[0]
+	return x - x<<c<<4
+}
+
+func g(x uint32) uint32 {
+	s := "\x04"
+	c := s[0]
+	return x - x<<c<<4
+}
+
+func main() {
+	if want, got := uint64(0xffffffffffffff01), f(1); want != got {
+		panic(fmt.Sprintf("want %x got %x", want, got))
+	}
+	if want, got := uint32(0xffffff01), g(1); want != got {
+		panic(fmt.Sprintf("want %x got %x", want, got))
+	}
+}