In this test, traditionally the comparison `*l == r[0]` was left as a
comparison between `*l` (type `any`) and `r[0]` (type `*int`), and the
rest of the compiler needed to handle mixed-typed comparisons.
However, this means more complexity for wiring up explicit rtypes.
To simplify rtype handling, the next CL will change unified IR to
instead handle the expression as `*l == any(r[0])`. However, a
consequence of this currently is that walk will now sequence the
`any(r[0])` expression first, because it involves a
concrete-to-interface conversion. And in turn, this means the `r[0]`
panic ("index out of bounds") will take priority over the `*l`
panic ("nil pointer dereference").
This is a change in user-visible semantics in some cases, but the Go
spec leaves this unspecified, so it shouldn't be an issue. Note also:
gccgo has the same behavior (i.e., panicking on index out of bounds,
not nil pointer dereference), and cmd/compile also already has the
same behavior when the interface conversion is explicit (as in the
added "nil pointer dereference #3" test case).
Updates #23735.
Updates #32187.
Change-Id: I49e5dcca85b4680f9c8780ef0013e64254d38fe5
Reviewed-on: https://go-review.googlesource.com/c/go/+/418097
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: David Chase <drchase@google.com>
In interface-to-concrete comparisons, we are short circuiting on the interface
value's dynamic type before evaluating the concrete expression for side effects,
causing concrete expression won't panic at runtime, while it should.
To fix it, evaluating the RHS of comparison before we do the short-circuit.
We also want to prioritize panics in the LHS over the RHS, so evaluating
the LHS too.
Fixes#32187
Change-Id: I15b58a523491b7fd1856b8fdb9ba0cba5d11ebb4
Reviewed-on: https://go-review.googlesource.com/c/go/+/178817
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
