bisect blames e41f527, paging @tzneal to the OR, stat!

It's now trying to inline switches (the point of the offending CL), but it doesn't know how to inline the fallthrough in k8s.io/kubernetes/pkg/api/resource/quantity.go:

// Neg sets q to the negative value of y.
// It updates the format of q to match y.
func (q *Quantity) Neg(y Quantity) error {
        switch {
        case y.Amount == nil:
                *q = y
        case q.Amount == nil:
                q.Amount = &inf.Dec{}
                fallthrough
        default:
                q.Amount.Neg(y.Amount)  
                q.Format = y.Format             
        }
        return nil
}

Removing the fallthrough makes it compile.

Marking fallthrough as hairy fixes it, but means that switch can no longer be inlined:

diff --git a/src/cmd/compile/internal/gc/inl.go b/src/cmd/compile/internal/gc/inl.go
index c21af77..230eb43 100644
--- a/src/cmd/compile/internal/gc/inl.go
+++ b/src/cmd/compile/internal/gc/inl.go
@@ -215,6 +215,7 @@ func ishairy(n *Node, budget *int) bool {
                OFOR,
                OSELECT,
                OTYPESW,
+               OXFALL,
                OPROC,
                ODEFER,
                ODCLTYPE, // can't print yet

I will leave to @tzneal or @dr2chase to fix.

Please notify me of the fix so I can update the corresponding binary exporter as well. Or leave fallthrough as "hairy" and wait until we switch over to binary format (soon-ish, code is working but needs to be reviewed and checked in.)

@griesemer @bradfitz thanks for the fix, I've verified it works and gets k8s building at tip again. I think it's a reasonable fix. I'll send a CL unless someone beats me to it this afternoon.

I've got a fix and unit test, but I'm in the middle of moving houses and my primary machine is still packed up. It's taking forever to run tests on this Macbook...

diff --git a/src/cmd/compile/internal/gc/fmt.go b/src/cmd/compile/internal/gc/fmt.go
index 7ed0851..72e1bc3 100644
--- a/src/cmd/compile/internal/gc/fmt.go
+++ b/src/cmd/compile/internal/gc/fmt.go
@@ -189,6 +189,7 @@ var goopnames = []string{
        OSUB:      "-",
        OSWITCH:   "switch",
        OXOR:      "^",
+       OXFALL:    "fallthrough",
 }

@tzneal Thanks.

CL https://golang.org/cl/21452 mentions this issue.