re = re.Simplify()
		if p, err = syntax.Compile(re); err != nil {
			t.Errorf("Compile(%q) got err:%s, want success", test.re, err)
			continue
		}
		isOnePass := compileOnePass(p) != nil
		if isOnePass != test.isOnePass {
			t.Errorf("CompileOnePass(%q) got isOnePass=%v, expected %v", test.re, isOnePass, test.isOnePass)
		}
	}
}

// TODO(cespare): Unify with onePassTests and rationalize one-pass test cases.

		}
	}
	return p
}

// compileOnePass returns a new *syntax.Prog suitable for onePass execution if the original Prog
// can be recharacterized as a one-pass regexp program, or syntax.nil if the
// Prog cannot be converted. For a one pass prog, the fundamental condition that must
// be true is: at any InstAlt, there must be no ambiguity about what branch to  take.
func compileOnePass(prog *syntax.Prog) (p *onePassProg) {

	if err != nil {
		t.Fatalf("parse: %v", err)
	}
	p, err := syntax.Compile(re.Simplify())
	if err != nil {
		t.Fatalf("compile: %v", err)
	}
	if compileOnePass(p) != nil {
		t.Fatalf("makeOnePass succeeded; wanted nil")
	}
}

// Check that the same machine can be used with the standard matcher
// and then the backtracker when there are no captures.

	if err != nil {
		return nil, err
	}
	matchcap := prog.NumCap
	if matchcap < 2 {
		matchcap = 2
	}
	regexp := &Regexp{
		expr:        expr,
		prog:        prog,
		onepass:     compileOnePass(prog),
		numSubexp:   maxCap,
		subexpNames: capNames,
		cond:        prog.StartCond(),
		longest:     longest,
		matchcap:    matchcap,
		minInputLen: minInputLen(re),
	}
	if regexp.onepass == nil {