You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: tighten.go
    path of file: ./repos/under-the-hood/gosrc/cmd/compile/internal/ssa
    
    the code of the file until where you have to start completion: // Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package ssa

// tighten moves Values closer to the Blocks in which they are used.
// This can reduce the amount of register spilling required,
// if it doesn't also create more live values.
// A Value can be moved to any 
    
func phiTighten(f *Func) {
	for _, b := range f.Blocks {
		for _, v := range b.Values {
			if v.Op != OpPhi {
				continue
			}
			for i, a := range v.Args {
				if !a.rematerializeable() {
					continue // not a constant we can move around
				}
				if a.Block == b.Preds[i].b {
					continue // already in the right place
				}
				// Make a copy of a, put in predecessor block.
				v.SetArg(i, a.copyInto(b.Preds[i].b))
			}
		}
	}
}