cmd/compile/internal/gc: inline autogenerated (*T).M wrappers

Currently all inlining of autogenerated wrappers is disabled,
because it causes build failures, when indexed export format is enabled.
Turns out we can reenable it for common case of (*T).M wrappers.
This fixes most performance degradation of 1.11 vs 1.10.

encoding/binary:
name                    old time/op   new time/op   delta
ReadSlice1000Int32s-6    14.8µs ± 2%   11.5µs ± 2%  -22.01%  (p=0.000 n=10+10)
WriteSlice1000Int32s-6   14.8µs ± 2%   11.7µs ± 2%  -20.95%  (p=0.000 n=10+10)

bufio:
name           old time/op    new time/op    delta
WriterFlush-6    32.4ns ± 1%    28.8ns ± 0%  -11.17%  (p=0.000 n=9+10)

sort:
SearchWrappers-6       231ns ± 1%   231ns ± 0%     ~     (p=0.129 n=9+10)
SortString1K-6         365µs ± 1%   298µs ± 1%  -18.43%  (p=0.000 n=9+10)
SortString1K_Slice-6   274µs ± 2%   276µs ± 1%     ~     (p=0.105 n=10+10)
StableString1K-6       490µs ± 1%   373µs ± 1%  -23.73%  (p=0.000 n=10+10)
SortInt1K-6            210µs ± 1%   142µs ± 1%  -32.69%  (p=0.000 n=10+10)
StableInt1K-6          243µs ± 0%   151µs ± 1%  -37.75%  (p=0.000 n=10+10)
StableInt1K_Slice-6    130µs ± 1%   130µs ± 0%     ~     (p=0.237 n=10+8)
SortInt64K-6          19.9ms ± 1%  13.5ms ± 1%  -32.32%  (p=0.000 n=10+10)
SortInt64K_Slice-6    11.5ms ± 1%  11.5ms ± 1%     ~     (p=0.912 n=10+10)
StableInt64K-6        21.5ms ± 0%  13.5ms ± 1%  -37.30%  (p=0.000 n=9+10)
Sort1e2-6              108µs ± 2%    83µs ± 3%  -23.26%  (p=0.000 n=10+10)
Stable1e2-6            218µs ± 0%   161µs ± 1%  -25.99%  (p=0.000 n=8+9)
Sort1e4-6             22.6ms ± 1%  16.8ms ± 0%  -25.45%  (p=0.000 n=10+7)
Stable1e4-6           67.6ms ± 1%  49.7ms ± 0%  -26.48%  (p=0.000 n=10+10)
Sort1e6-6              3.44s ± 0%   2.55s ± 1%  -26.05%  (p=0.000 n=8+9)
Stable1e6-6            13.7s ± 0%    9.9s ± 1%  -27.68%  (p=0.000 n=8+10)

Fixes #27621
Updates #25338

Change-Id: I6fe633202f63fa829a6ab849c44d7e45f8835dff
Reviewed-on: https://go-review.googlesource.com/c/135697
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/inl_test.go

@@ -26,7 +26,8 @@ func TestIntendedInlining(t *testing.T) {
 	t.Parallel()
 
 	// want is the list of function names (by package) that should
-	// be inlined.
+	// be inlinable. If they have no callers in thier packages, they
+	// might not actually be inlined anywhere.
 	want := map[string][]string{
 		"runtime": {
 			// TODO(mvdan): enable these once mid-stack
@@ -111,6 +112,11 @@ func TestIntendedInlining(t *testing.T) {
 			"(*Buffer).UnreadByte",
 			"(*Buffer).tryGrowByReslice",
 		},
+		"compress/flate": {
+			"byLiteral.Len",
+			"byLiteral.Less",
+			"byLiteral.Swap",
+		},
 		"unicode/utf8": {
 			"FullRune",
 			"FullRuneInString",
@@ -162,6 +168,13 @@ func TestIntendedInlining(t *testing.T) {
 		want["runtime"] = append(want["runtime"], "rotl_31")
 	}
 
+	// Functions that must actually be inlined; they must have actual callers.
+	must := map[string]bool{
+		"compress/flate.byLiteral.Len":  true,
+		"compress/flate.byLiteral.Less": true,
+		"compress/flate.byLiteral.Swap": true,
+	}
+
 	notInlinedReason := make(map[string]string)
 	pkgs := make([]string, 0, len(want))
 	for pname, fnames := range want {
@@ -188,6 +201,7 @@ func TestIntendedInlining(t *testing.T) {
 	scanner := bufio.NewScanner(pr)
 	curPkg := ""
 	canInline := regexp.MustCompile(`: can inline ([^ ]*)`)
+	haveInlined := regexp.MustCompile(`: inlining call to ([^ ]*)`)
 	cannotInline := regexp.MustCompile(`: cannot inline ([^ ]*): (.*)`)
 	for scanner.Scan() {
 		line := scanner.Text()
@@ -195,11 +209,20 @@ func TestIntendedInlining(t *testing.T) {
 			curPkg = line[2:]
 			continue
 		}
-		if m := canInline.FindStringSubmatch(line); m != nil {
+		if m := haveInlined.FindStringSubmatch(line); m != nil {
 			fname := m[1]
 			delete(notInlinedReason, curPkg+"."+fname)
 			continue
 		}
+		if m := canInline.FindStringSubmatch(line); m != nil {
+			fname := m[1]
+			fullname := curPkg + "." + fname
+			// If function must be inlined somewhere, beeing inlinable is not enough
+			if _, ok := must[fullname]; !ok {
+				delete(notInlinedReason, fullname)
+				continue
+			}
+		}
 		if m := cannotInline.FindStringSubmatch(line); m != nil {
 			fname, reason := m[1], m[2]
 			fullName := curPkg + "." + fname

src/cmd/compile/internal/gc/subr.go

@@ -1728,11 +1728,10 @@ func genwrapper(rcvr *types.Type, method *types.Field, newnam *types.Sym) {
 	Curfn = fn
 	typecheckslice(fn.Nbody.Slice(), Etop)
 
-	// TODO(mdempsky): Investigate why this doesn't work with
-	// indexed export. For now, we disable even in non-indexed
-	// mode to ensure fair benchmark comparisons and to track down
-	// unintended compilation differences.
-	if false {
+	// Inline calls within (*T).M wrappers. This is safe because we only
+	// generate those wrappers within the same compilation unit as (T).M.
+	// TODO(mdempsky): Investigate why we can't enable this more generally.
+	if rcvr.IsPtr() && rcvr.Elem() == method.Type.Recv().Type && rcvr.Elem().Sym != nil {
 		inlcalls(fn)
 	}
 	escAnalyze([]*Node{fn}, false)