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Updated CompilerOptimizations (markdown)

Josh Bleecher Snyder 2015-02-04 09:50:03 -08:00
parent 5871177867
commit 5afa467228
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CompilerOptimizations.md

@ -2,31 +2,48 @@
This page lists optimizations done by the compilers. Note that these are not guaranteed by the language specification. 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. Putting a zero-width type in an interface value doesn't allocate.
* **gc:** 1.0+ * **gc:** 1.0+
* **gccgo:** ? * **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. 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+ * **gc:** 1.0-1.3, but *not* in 1.4+
* **gccgo:** never * **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) 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+ * **gc:** 1.4+
* **gccgo:** ? * **gccgo:** ?
## Escape analysis: foo ## Escape analysis
TODO 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:** ?