runtime/pprof: include PCs for deduplication in TestMutexBlockFullAggregation

TestMutexBlockFullAggregation aggregates stacks by function, file, and
line number. But there can be multiple function calls on the same line,
giving us different sequences of PCs. This causes the test to spuriously
fail in some cases. Include PCs in the stacks for this test.

Also pick up a small "range over int" modernize suggestion while we're
looking at the test.

Fixes #73641

Change-Id: I50489e19fcf920e27b9eebd9d4b35feb89981cbc
Reviewed-on: https://go-review.googlesource.com/c/go/+/673115
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: nsrip-dd

src/runtime/pprof/pprof_test.go

@@ -2632,7 +2632,7 @@ func produceProfileEvents(t *testing.T, depth int) {
 	goroutineDeep(t, depth-4) // -4 for produceProfileEvents, **, chanrecv1, chanrev, gopark
 }
 
-func getProfileStacks(collect func([]runtime.BlockProfileRecord) (int, bool), fileLine bool) []string {
+func getProfileStacks(collect func([]runtime.BlockProfileRecord) (int, bool), fileLine bool, pcs bool) []string {
 	var n int
 	var ok bool
 	var p []runtime.BlockProfileRecord
@@ -2651,6 +2651,9 @@ func getProfileStacks(collect func([]runtime.BlockProfileRecord) (int, bool), fi
 			if i > 0 {
 				stack.WriteByte('\n')
 			}
+			if pcs {
+				fmt.Fprintf(&stack, "%x ", pc)
+			}
 			// Use FuncForPC instead of CallersFrames,
 			// because we want to see the info for exactly
 			// the PCs returned by the mutex profile to
@@ -2691,9 +2694,9 @@ func TestMutexBlockFullAggregation(t *testing.T) {
 
 	wg := sync.WaitGroup{}
 	wg.Add(workers)
-	for j := 0; j < workers; j++ {
+	for range workers {
 		go func() {
-			for i := 0; i < iters; i++ {
+			for range iters {
 				m.Lock()
 				// Wait at least 1 millisecond to pass the
 				// starvation threshold for the mutex
@@ -2706,7 +2709,7 @@ func TestMutexBlockFullAggregation(t *testing.T) {
 	wg.Wait()
 
 	assertNoDuplicates := func(name string, collect func([]runtime.BlockProfileRecord) (int, bool)) {
-		stacks := getProfileStacks(collect, true)
+		stacks := getProfileStacks(collect, true, true)
 		seen := make(map[string]struct{})
 		for _, s := range stacks {
 			if _, ok := seen[s]; ok {
@@ -2782,7 +2785,7 @@ runtime/pprof.inlineA`,
 
 	for _, tc := range tcs {
 		t.Run(tc.Name, func(t *testing.T) {
-			stacks := getProfileStacks(tc.Collect, false)
+			stacks := getProfileStacks(tc.Collect, false, false)
 			for _, s := range stacks {
 				if strings.Contains(s, tc.SubStack) {
 					return