runtime: add gc layout info for some basic types

src/runtime/slice.go

@@ -3,6 +3,7 @@ package runtime
 // This file implements compiler builtins for slices: append() and copy().
 
 import (
+	"internal/gclayout"
 	"math/bits"
 	"unsafe"
 )
@@ -47,7 +48,13 @@ func sliceGrow(oldBuf unsafe.Pointer, oldLen, oldCap, newCap, elemSize uintptr)
 	// memory allocators, this causes some difficult to debug issues.
 	newCap = 1 << bits.Len(uint(newCap))
 
-	buf := alloc(newCap*elemSize, nil)
+	var layout unsafe.Pointer
+	// less type info here; can only go off element size
+	if elemSize < unsafe.Sizeof(uintptr(0)) {
+		layout = gclayout.NoPtrs
+	}
+
+	buf := alloc(newCap*elemSize, layout)
 	if oldLen > 0 {
 		// copy any data to new slice
 		memmove(buf, oldBuf, oldLen*elemSize)

src/runtime/string.go

@@ -3,6 +3,7 @@ package runtime
 // This file implements functions related to Go strings.
 
 import (
+	"internal/gclayout"
 	"unsafe"
 )
 
@@ -59,7 +60,7 @@ func stringConcat(x, y _string) _string {
 		return x
 	} else {
 		length := x.length + y.length
-		buf := alloc(length, nil)
+		buf := alloc(length, gclayout.NoPtrs)
 		memcpy(buf, unsafe.Pointer(x.ptr), x.length)
 		memcpy(unsafe.Add(buf, x.length), unsafe.Pointer(y.ptr), y.length)
 		return _string{ptr: (*byte)(buf), length: length}
@@ -72,7 +73,7 @@ func stringFromBytes(x struct {
 	len uintptr
 	cap uintptr
 }) _string {
-	buf := alloc(x.len, nil)
+	buf := alloc(x.len, gclayout.NoPtrs)
 	memcpy(buf, unsafe.Pointer(x.ptr), x.len)
 	return _string{ptr: (*byte)(buf), length: x.len}
 }
@@ -83,7 +84,7 @@ func stringToBytes(x _string) (slice struct {
 	len uintptr
 	cap uintptr
 }) {
-	buf := alloc(x.length, nil)
+	buf := alloc(x.length, gclayout.NoPtrs)
 	memcpy(buf, unsafe.Pointer(x.ptr), x.length)
 	slice.ptr = (*byte)(buf)
 	slice.len = x.length
@@ -100,7 +101,7 @@ func stringFromRunes(runeSlice []rune) (s _string) {
 	}
 
 	// Allocate memory for the string.
-	s.ptr = (*byte)(alloc(s.length, nil))
+	s.ptr = (*byte)(alloc(s.length, gclayout.NoPtrs))
 
 	// Encode runes to UTF-8 and store the resulting bytes in the string.
 	index := uintptr(0)