cmd/compile: make runtime/internal/sys.NotInHeap intrinsic

So next CL can get rid of go:notinheap pragma.

Updates #46731

Change-Id: Ib2e2f2d381767e11cec10f76261b516188ddaa6a
Reviewed-on: https://go-review.googlesource.com/c/go/+/422814
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/compile/internal/types/size.go

@@ -184,6 +184,13 @@ func calcStructOffset(errtype *Type, t *Type, o int64, flag int) int64 {
 		}
 
 		CalcSize(f.Type)
+		// If type T contains a field F marked as not-in-heap,
+		// then T must also be a not-in-heap type. Otherwise,
+		// you could heap allocate T and then get a pointer F,
+		// which would be a heap pointer to a not-in-heap type.
+		if f.Type.NotInHeap() {
+			t.SetNotInHeap(true)
+		}
 		if int32(f.Type.align) > maxalign {
 			maxalign = int32(f.Type.align)
 		}
@@ -391,6 +398,7 @@ func CalcSize(t *Type) {
 		}
 
 		CalcSize(t.Elem())
+		t.SetNotInHeap(t.Elem().NotInHeap())
 		if t.Elem().width != 0 {
 			cap := (uint64(MaxWidth) - 1) / uint64(t.Elem().width)
 			if uint64(t.NumElem()) > cap {
@@ -412,6 +420,10 @@ func CalcSize(t *Type) {
 		if t.IsFuncArgStruct() {
 			base.Fatalf("CalcSize fn struct %v", t)
 		}
+		// Recognize and mark runtime/internal/sys.nih as not-in-heap.
+		if sym := t.Sym(); sym != nil && sym.Pkg.Path == "runtime/internal/sys" && sym.Name == "nih" {
+			t.SetNotInHeap(true)
+		}
 		w = calcStructOffset(t, t, 0, 1)
 
 	// make fake type to check later to

src/cmd/compile/internal/types/type.go

@@ -625,7 +625,6 @@ func NewArray(elem *Type, bound int64) *Type {
 	}
 	t := newType(TARRAY)
 	t.extra = &Array{Elem: elem, Bound: bound}
-	t.SetNotInHeap(elem.NotInHeap())
 	if elem.HasTParam() {
 		t.SetHasTParam(true)
 	}
@@ -1061,17 +1060,6 @@ func (t *Type) SetFields(fields []*Field) {
 		base.Fatalf("SetFields of %v: width previously calculated", t)
 	}
 	t.wantEtype(TSTRUCT)
-	for _, f := range fields {
-		// If type T contains a field F with a go:notinheap
-		// type, then T must also be go:notinheap. Otherwise,
-		// you could heap allocate T and then get a pointer F,
-		// which would be a heap pointer to a go:notinheap
-		// type.
-		if f.Type != nil && f.Type.NotInHeap() {
-			t.SetNotInHeap(true)
-			break
-		}
-	}
 	t.Fields().Set(fields)
 }
 
@@ -1676,7 +1664,7 @@ func (t *Type) IsUntyped() bool {
 }
 
 // HasPointers reports whether t contains a heap pointer.
-// Note that this function ignores pointers to go:notinheap types.
+// Note that this function ignores pointers to not-in-heap types.
 func (t *Type) HasPointers() bool {
 	return PtrDataSize(t) > 0
 }

src/runtime/internal/sys/nih.go

@@ -4,9 +4,8 @@
 
 package sys
 
-// TODO: make this as a compiler intrinsic type, and remove go:notinheap
-//
-//go:notinheap
+// NOTE: keep in sync with cmd/compile/internal/types.CalcSize
+// to make the compiler recognize this as an intrinsic type.
 type nih struct{}
 
 // NotInHeap is a type must never be allocated from the GC'd heap or on the stack,