cmd/cgo: optimize cgoCheckPointer call

Currently cgoCheckPointer is only used with one optional argument.
Using a slice for the optional arguments is quite expensive, hence
replace it with a single interface{}. This results in ~30% improvement.

When checking struct fields, they quite often end up being without
pointers. Check this before calling cgoCheckPointer, which results in
additional ~20% improvement.

Inline some p == nil checks from cgoIsGoPointer which gives
additional ~15% improvement.

All of this translates to:

name                             old time/op  new time/op  delta
CgoCall/add-int-32               46.9ns ± 1%  46.6ns ± 1%   -0.75%  (p=0.000 n=18+20)
CgoCall/one-pointer-32            143ns ± 1%    87ns ± 1%  -38.96%  (p=0.000 n=20+20)
CgoCall/eight-pointers-32         767ns ± 0%   327ns ± 1%  -57.30%  (p=0.000 n=18+16)
CgoCall/eight-pointers-nil-32     110ns ± 1%    89ns ± 2%  -19.10%  (p=0.000 n=19+19)
CgoCall/eight-pointers-array-32  5.09µs ± 1%  3.56µs ± 2%  -30.09%  (p=0.000 n=19+19)
CgoCall/eight-pointers-slice-32  3.92µs ± 0%  2.57µs ± 2%  -34.48%  (p=0.000 n=20+20)

Change-Id: I2aa9f5ae8962a9a41a7fb1db0c300893109d0d75
Reviewed-on: https://go-review.googlesource.com/c/go/+/198081
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 12 insertions, 6 deletions

diff --git a/src/runtime/cgocall.go b/src/runtime/cgocall.go
index a881ae1489..3595e49ed5 100644
--- a/src/runtime/cgocall.go
+++ b/src/runtime/cgocall.go
@@ -406,7 +406,7 @@ var racecgosync uint64 // represents possible synchronization in C code
 
 // cgoCheckPointer checks if the argument contains a Go pointer that
 // points to a Go pointer, and panics if it does.
-func cgoCheckPointer(ptr interface{}, args ...interface{}) {
+func cgoCheckPointer(ptr interface{}, arg interface{}) {
 	if debug.cgocheck == 0 {
 		return
 	}
@@ -415,15 +415,15 @@ func cgoCheckPointer(ptr interface{}, args ...interface{}) {
 	t := ep._type
 
 	top := true
-	if len(args) > 0 && (t.kind&kindMask == kindPtr || t.kind&kindMask == kindUnsafePointer) {
+	if arg != nil && (t.kind&kindMask == kindPtr || t.kind&kindMask == kindUnsafePointer) {
 		p := ep.data
 		if t.kind&kindDirectIface == 0 {
 			p = *(*unsafe.Pointer)(p)
 		}
-		if !cgoIsGoPointer(p) {
+		if p == nil || !cgoIsGoPointer(p) {
 			return
 		}
-		aep := (*eface)(unsafe.Pointer(&args[0]))
+		aep := (*eface)(unsafe.Pointer(&arg))
 		switch aep._type.kind & kindMask {
 		case kindBool:
 			if t.kind&kindMask == kindUnsafePointer {
@@ -460,7 +460,7 @@ const cgoResultFail = "cgo result has Go pointer"
 // depending on indir. The top parameter is whether we are at the top
 // level, where Go pointers are allowed.
 func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) {
-	if t.ptrdata == 0 {
+	if t.ptrdata == 0 || p == nil {
 		// If the type has no pointers there is nothing to do.
 		return
 	}
@@ -517,7 +517,7 @@ func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) {
 		st := (*slicetype)(unsafe.Pointer(t))
 		s := (*slice)(p)
 		p = s.array
-		if !cgoIsGoPointer(p) {
+		if p == nil || !cgoIsGoPointer(p) {
 			return
 		}
 		if !top {
@@ -548,11 +548,17 @@ func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) {
 			return
 		}
 		for _, f := range st.fields {
+			if f.typ.ptrdata == 0 {
+				continue
+			}
 			cgoCheckArg(f.typ, add(p, f.offset()), true, top, msg)
 		}
 	case kindPtr, kindUnsafePointer:
 		if indir {
 			p = *(*unsafe.Pointer)(p)
+			if p == nil {
+				return
+			}
 		}
 
 		if !cgoIsGoPointer(p) {