// their dependencies).
	setToolFlags(pkgs...)

	setPGOProfilePath(pkgs)

	return pkgs
}

// setPGOProfilePath sets the PGO profile path for pkgs.
// In -pgo=auto mode, it finds the default PGO profile.
func setPGOProfilePath(pkgs []*Package) {
	updateBuildInfo := func(p *Package, file string) {
		// Don't create BuildInfo for packages that didn't already have it.

// pointer from a well-known register (DX on x86 architecture, etc.) directly.
//
// WARNING: PGO-based devirtualization cannot detect that caller of
// getclosureptr require closure context, and thus must maintain a list of
// these functions, which is in
// cmd/compile/internal/devirtualize/pgo.maybeDevirtualizeFunctionCall.
func getclosureptr() uintptr

//go:noescape

		// See golang.org/issue/30907, golang.org/issue/34114.
		if p.Name == "main" && p != pmain && p != ptest {
			split()
		}
		// Split and attach PGO information to test dependencies if preal
		// is built with PGO.
		if preal.Internal.PGOProfile != "" && p.Internal.PGOProfile == "" {
			split()
		}
	}

	// Do search to find cycle.

		return true
	}

	// Check to see if the action output is cached.
	if file, _, err := cache.GetFile(c, actionHash); err == nil {
		if a.Mode == "preprocess PGO profile" {
			// Preprocessed PGO profiles don't embed a build ID, so
			// skip the build ID lookup.
			// TODO(prattmic): better would be to add a build ID to the format.
			a.built = file
			a.Target = "DO NOT USE - using cache"

	BuildN             bool                    // -n flag
	BuildO             string                  // -o flag
	BuildP             = runtime.GOMAXPROCS(0) // -p flag
	BuildPGO           string                  // -pgo flag
	BuildPkgdir        string                  // -pkgdir flag
	BuildRace          bool                    // -race flag
	BuildToolexec      []string                // -toolexec flag
	BuildToolchainName string

	// Now that cmd/go is in charge of the build process, enable GOEXPERIMENT.
	os.Setenv("GOEXPERIMENT", goexperiment)
	// No need to enable PGO for toolchain2.
	goInstall(toolenv(), goBootstrap, append([]string{"-pgo=off"}, toolchain...)...)
	if debug {
		run("", ShowOutput|CheckExit, pathf("%s/compile", tooldir), "-V=full")

			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.