cmd/compile: do not report division by error during typecheck

types2 have already errored about any spec-required overflows, and
division by zero. CL 469595 unintentionally fixed typecheck not to error
about overflows, but zero division is still be checked during tcArith.
This causes unsafe operations with variable size failed to compile,
instead of raising runtime error.

Fixes #60601

Change-Id: I7bea2821099556835c920713397f7c5d8a4025ac
Reviewed-on: https://go-review.googlesource.com/c/go/+/501735
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/cmd/compile/internal/typecheck/expr.go

@@ -184,13 +184,6 @@ func tcArith(n ir.Node, op ir.Op, l, r ir.Node) (ir.Node, ir.Node, *types.Type)
 		}
 	}
 
-	if (op == ir.ODIV || op == ir.OMOD) && ir.IsConst(r, constant.Int) {
-		if constant.Sign(r.Val()) == 0 {
-			base.Errorf("division by zero")
-			return l, r, nil
-		}
-	}
-
 	return l, r, t
 }
 

test/fixedbugs/issue60601.go

@@ -0,0 +1,50 @@
+// run
+
+// Copyright 2023 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 (
+	"strings"
+	"unsafe"
+)
+
+func shift[T any]() int64 {
+	return 1 << unsafe.Sizeof(*new(T))
+}
+
+func div[T any]() uintptr {
+	return 1 / unsafe.Sizeof(*new(T))
+}
+
+func add[T any]() int64 {
+	return 1<<63 - 1 + int64(unsafe.Sizeof(*new(T)))
+}
+
+func main() {
+	shift[[62]byte]()
+	shift[[63]byte]()
+	shift[[64]byte]()
+	shift[[100]byte]()
+	shift[[1e6]byte]()
+
+	add[[1]byte]()
+	shouldPanic("divide by zero", func() { div[[0]byte]() })
+}
+
+func shouldPanic(str string, f func()) {
+	defer func() {
+		err := recover()
+		if err == nil {
+			panic("did not panic")
+		}
+		s := err.(error).Error()
+		if !strings.Contains(s, str) {
+			panic("got panic " + s + ", want " + str)
+		}
+	}()
+
+	f()
+}