## 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}

In all these examples, the solution is the same:
use explicit synchronization.
</p>

<h2 id="badcompiler">Incorrect compilation</h2>

<p>
The Go memory model restricts compiler optimizations as much as it does Go programs.
Some compiler optimizations that would be valid in single-threaded programs are not valid in all Go programs.
In particular, a compiler must not introduce writes that do not exist in the original program,

	// TODO(rsc): require failure
	args := p.gccCmd()

	// Optimization options can confuse the error messages; remove them.
	nargs := make([]string, 0, len(args)+len(extraArgs))
	for _, arg := range args {
		if !strings.HasPrefix(arg, "-O") {
			nargs = append(nargs, arg)
		}
	}

	// Force -O0 optimization and append extra arguments, but keep the
	// trailing "-" at the end.

<li>The global generator accessed by top-level functions is unconditionally randomly seeded.
Because the API guarantees no fixed sequence of results,
optimizations like per-thread random generator states are now possible.

<li>The <a href="/pkg/math/rand/v2/#Source"><code>Source</code></a>
interface now has a single <code>Uint64</code> method;