diff --git a/CompilerOptimizations.md b/CompilerOptimizations.md
index 5f8d5a45..a960d6c2 100644
--- a/CompilerOptimizations.md
+++ b/CompilerOptimizations.md
@@ -2,31 +2,48 @@
 
 This page lists optimizations done by the compilers. Note that these are not guaranteed by the language specification.
 
-## Zero-width types in interface values
+## Interface values
+
+### Zero-width types in interface values
 
 Putting a zero-width type in an interface value doesn't allocate.
 
 * **gc:** 1.0+
 * **gccgo:** ?
 
-## Word-sized value in an interface value
+### Word-sized value in an interface value
 
 Putting a word-sized-or-less non-pointer type in an interface value doesn't allocate.
 
 * **gc:** 1.0-1.3, but *not* in 1.4+
 * **gccgo:** never
 
-## Map lookup by []byte
+## string and []byte
+
+### Map lookup by []byte
 
 For a map m of type map[string]T and []byte b, m[string(b)] doesn't allocate. (the temporary string copy of the byte slice isn't made)
 
 * **gc:** 1.4+
 * **gccgo:** ?
 
-## Escape analysis: foo
+## Escape analysis
 
 TODO
 
-## Escape analysis: bar
+## Idioms
 
-TODO
+### Optimized memclr
+
+For a slice or array s, loops of the form
+
+```go
+for i := range s {
+	a[i] = <zero value for element of s>
+}
+```
+
+are converted into efficient runtime memclr calls. [Issue](golang.org/issue/5373) and [commit](https://golang.org/change/f03c9202c43e0abb130669852082117ca50aa9b1).
+
+* **gc:** 1.5+
+* **gccgo:** ?