This section documents the GODEBUG settings introduced and removed in each major Go release
for compatibility reasons.
Packages or programs may define additional settings for internal debugging purposes;
for example,
see the [runtime documentation](/pkg/runtime#hdr-Environment_Variables)
and the [go command documentation](/cmd/go#hdr-Build_and_test_caching).

### Go 1.23

denotes the field or method <code>f</code> of the value <code>x</code>
(or sometimes <code>*x</code>; see below).
The identifier <code>f</code> is called the (field or method) <i>selector</i>;
it must not be the <a href="#Blank_identifier">blank identifier</a>.
The type of the selector expression is the type of <code>f</code>.
If <code>x</code> is a package name, see the section on
<a href="#Qualified_identifiers">qualified identifiers</a>.
</p>

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## Compiler {#compiler}

The build time overhead to building with [Profile Guided Optimization](/doc/pgo) has been reduced significantly.
Previously, large builds could see 100%+ build time increase from enabling PGO.
In Go 1.23, overhead should be in the single digit percentages.

## Assembler {#assembler}