## 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.

<!-- https://go.dev/issue/62737 , https://golang.org/cl/576681,  https://golang.org/cl/577615 -->
The compiler in Go 1.23 can now overlap the stack frame slots of local variables

			return fmt.Errorf("marshal embedcfg: %v", err)
		}
		embedcfg = js
	}

	// Find PGO profile if needed.
	var pgoProfile string
	for _, a1 := range a.Deps {
		if a1.Mode != "preprocess PGO profile" {
			continue
		}
		if pgoProfile != "" {
			return fmt.Errorf("action contains multiple PGO profile dependencies")
		}
		pgoProfile = a1.built
	}

//		run through go run and go test respectively.
//	-pgo file
//		specify the file path of a profile for profile-guided optimization (PGO).
//		When the special name "auto" is specified, for each main package in the
//		build, the go command selects a file named "default.pgo" in the package's
//		directory if that file exists, and applies it to the (transitive)

			// So far this has only been shown profitable for PGO-hot loop headers.
			// The Hotness values allows distinctions betwen initial blocks that are "hot" or not, and "flow-in" or not.
			// Currently only the initial blocks of loops are tagged in this way;
			// there are no blocks tagged "pgo-hot" that are not also tagged "initial".
			// TODO more heuristics, more architectures.