cmd/compile: inlining budget excludes cross-package calls #22194
Description
In the example below, p.G and q.H are identical, except that p.G is in the same package as p.F, yet cmd/compile decides that q.H is inlineable whereas p.G is not.
This is because cmd/compile currently only computes Inlcost for locally defined functions. Calls to functions in external packages are effectively treated as free.
$ go tool compile -m p.go
p.go:3:6: can inline F
p.go:13:3: inlining call to F
$ go tool compile -m q.go
q.go:5:6: can inline H
q.go:6:5: inlining call to p.F
$ cat p.go
package p
func F() {
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
}
func G() {
F()
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
}
$ cat q.go
package q
import "./p"
func H() {
p.F()
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
}