diff --git a/src/cmd/compile/internal/ssa/cache.go b/src/cmd/compile/internal/ssa/cache.go
new file mode 100644
index 0000000000..64f9659520
--- /dev/null
+++ b/src/cmd/compile/internal/ssa/cache.go
@@ -0,0 +1,10 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ssa
+
+// A Cache holds reusable compiler state.
+// It is intended to be re-used for multiple Func compilations.
+type Cache struct {
+}
diff --git a/src/cmd/compile/internal/ssa/config.go b/src/cmd/compile/internal/ssa/config.go
index 52692847b9..978c0d6fa8 100644
--- a/src/cmd/compile/internal/ssa/config.go
+++ b/src/cmd/compile/internal/ssa/config.go
@@ -14,6 +14,9 @@ import (
 	"strings"
 )
 
+// A Config holds readonly compilation information.
+// It is created once, early during compilation,
+// and shared across all compilations.
 type Config struct {
 	arch            string                     // "amd64", etc.
 	IntSize         int64                      // 4 or 8
diff --git a/src/cmd/compile/internal/ssa/func.go b/src/cmd/compile/internal/ssa/func.go
index 5dc352e991..75b5b44a96 100644
--- a/src/cmd/compile/internal/ssa/func.go
+++ b/src/cmd/compile/internal/ssa/func.go
@@ -11,8 +11,9 @@ import (
 	"strings"
 )
 
-// A Func represents a Go func declaration (or function literal) and
-// its body. This package compiles each Func independently.
+// A Func represents a Go func declaration (or function literal) and its body.
+// This package compiles each Func independently.
+// Funcs are single-use; a new Func must be created for every compiled function.
 type Func struct {
 	Config *Config  // architecture information
 	pass   *pass    // current pass information (name, options, etc.)