cmd/compile: encourage inlining of functions with single-call bodies

This is a simple tweak to allow a bit more mid-stack inlining.
In cases like this:

func f() {
    g()
}

We'd really like to inline f into its callers. It can't hurt.

We implement this optimization by making calls a bit cheaper, enough
to afford a single call in the function body, but not 2.
The remaining budget allows for some argument modification, or perhaps
a wrapping conditional:

func f(x int) {
    g(x, 0)
}
func f(x int) {
    if x > 0 {
        g()
    }
}

Update #19348

Change-Id: Ifb1ea0dd1db216c3fd5c453c31c3355561fe406f
Reviewed-on: https://go-review.googlesource.com/c/147361
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: David Chase <drchase@google.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/runtime/stack_test.go b/src/runtime/stack_test.go
index dc65395141..f52381710d 100644
--- a/src/runtime/stack_test.go
+++ b/src/runtime/stack_test.go
@@ -595,6 +595,9 @@ func (s structWithMethod) callers() []uintptr {
 	return pc[:Callers(0, pc)]
 }
 
+// The noinline prevents this function from being inlined
+// into a wrapper. TODO: remove this when issue 28640 is fixed.
+//go:noinline
 func (s structWithMethod) stack() string {
 	buf := make([]byte, 4<<10)
 	return string(buf[:Stack(buf, false)])