cmd/compile: sort liveness variable reports

Sort variables before display so that when there are multiple variables
to report, they are in a consistent order.

Otherwise they are ordered in the order they appear in the fn.Dcl list,
which can vary. Particularly, they vary depending on regabi.

Change-Id: I0db380f7cbe6911e87177503a4c3b39851ff1b5a
Reviewed-on: https://go-review.googlesource.com/c/go/+/462898
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/cmd/compile/internal/liveness/plive.go

@@ -1106,11 +1106,18 @@ func (lv *liveness) showlive(v *ssa.Value, live bitvec.BitVec) {
 		s += "indirect call:"
 	}
 
+	// Sort variable names for display. Variables aren't in any particular order, and
+	// the order can change by architecture, particularly with differences in regabi.
+	var names []string
 	for j, n := range lv.vars {
 		if live.Get(int32(j)) {
-			s += fmt.Sprintf(" %v", n)
+			names = append(names, n.Sym().Name)
 		}
 	}
+	sort.Strings(names)
+	for _, v := range names {
+		s += " " + v
+	}
 
 	base.WarnfAt(pos, s)
 }

test/live.go

@@ -698,9 +698,9 @@ func f41(p, q *int) (r *int) { // ERROR "live at entry to f41: p q$"
 	defer func() {
 		recover()
 	}()
-	printint(0) // ERROR "live at call to printint: q r .autotmp_[0-9]+$"
+	printint(0) // ERROR "live at call to printint: .autotmp_[0-9]+ q r$"
 	r = q
-	return // ERROR "live at call to f41.func1: r .autotmp_[0-9]+$"
+	return // ERROR "live at call to f41.func1: .autotmp_[0-9]+ r$"
 }
 
 func f42() {

test/live_regabi.go

@@ -693,7 +693,7 @@ func f41(p, q *int) (r *int) { // ERROR "live at entry to f41: p q$"
 	defer func() {
 		recover()
 	}()
-	printint(0) // ERROR "live at call to printint: q .autotmp_[0-9]+ r$"
+	printint(0) // ERROR "live at call to printint: .autotmp_[0-9]+ q r$"
 	r = q
 	return // ERROR "live at call to f41.func1: .autotmp_[0-9]+ r$"
 }