The following program behaves differently depending on whether or not it's compiled with SSA:

package main

type Closer interface {
    Close()
}

func main() {
    var x Closer
    defer x.Close()
    println("not reached")
}

When compiled without SSA, it does not print "not reached". However, when compiled with SSA, it does print "not reached". Based on my understanding of the spec, this program should not print "not reached" because the evaluation of x.Close to a function value happens on the defer line and should cause a nil panic (though either way it shouldn't change with SSA).

$ go run -gcflags -ssa=0 x.go
panic: runtime error: invalid memory address or nil pointer dereference
...

$ go run x.go
not reached
panic: runtime error: invalid memory address or nil pointer dereference

This pattern appears in test/fixedbugs/issue6055.go.

/cc @cherrymui @randall77