The Go compiler’s SSA backend contains a facility to produce HTML debugging output of the compilation phases. This post covers how to print the SSA output for function _and_ methods.
Let’s start with a sample program which contains a function, a value method, and a pointer method:
```
package main
import (
"fmt"
)
type Numbers struct {
vals []int
}
func (n *Numbers) Add(v int) {
n.vals = append(n.vals, v)
}
func (n Numbers) Average() float64 {
sum := 0.0
for _, num := range n.vals {
sum += float64(num)
}
return sum / float64(len(n.vals))
}
func main() {
var numbers Numbers
numbers.Add(200)
numbers.Add(43)
numbers.Add(-6)
fmt.Println(numbers.Average())
}
```
Control of the SSA debugging output is via the `GOSSAFUNC` environment variable. This variable takes the name of the function to dump. This is _not_ the functions fully qualified name. For `func main` above the name of the function is `main`_not_`main.main`.
```
% env GOSSAFUNC=main go build
runtime
dumped SSA to ../../go/src/runtime/ssa.html
t
dumped SSA to ./ssa.html
```
In this example `GOSSAFUNC=main` matched both `main.main` and a function called `runtime.main`.[1][1] This is a little unfortunate, but in practice probably not a big deal as, if you’re performance tuning your code, it won’t be in a giant spaghetti blob in `func main`.
What is more likely is your code will be in a _method_, so you’ve probably landed on this post looking for the correct incantation to dump the SSA output for a method.
To print the SSA debug for the pointer method `func (n *Numbers) Add`, the equivalent function name is`(*Numbers).Add`:[2][2]
```
% env "GOSSAFUNC=(*Numbers).Add" go build
t
dumped SSA to ./ssa.html
```
To print the SSA debug for a value method `func (n Numbers) Average`, the equivalent function name is `(*Numbers).Average`_even though this is a value method_:
```
% env "GOSSAFUNC=(*Numbers).Average" go build
t
dumped SSA to ./ssa.html
```
1. If you didn’t build Go from source then the path to the `runtime` package may be read only and you might receive an error. Please don’t use the `sudo` hammer to fix this.[][3]
2. Please pay attention to the shell quoting.[][4]
### Related posts:
1. [Accidental method value][5]
2. [Never edit a method, always rewrite it][6]
3. [How to find out which Go version built your binary][7]
[1]: tmp.kLSHpQXzhr#easy-footnote-bottom-1-4188 (If you didn’t build Go from source then the path to the <code>runtime</code> package may be read only and you might receive an error. Please don’t use the <code>sudo</code> hammer to fix this.)
[2]: tmp.kLSHpQXzhr#easy-footnote-bottom-2-4188 (Please pay attention to the shell quoting.)
