Compiler Optimizations

This page lists optimizations done by the compilers. Note that these are not guaranteed by the language specification.

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

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

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

TODO

Idioms

Optimized memclr

For a slice or array s, loops of the form

for i := range s {
	a[i] = <zero value for element of s>
}

are converted into efficient runtime memclr calls. Issue and commit.

• gc: 1.5+
• gccgo: ?