Updated CompilerOptimizations (markdown)
diff --git a/CompilerOptimizations.md b/CompilerOptimizations.md
index 5f8d5a4..a960d6c 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:** ?
