cmd/compile: remove Type haspointers caches

Even very large Types are not very big.
The haspointer cache looks like premature optimization.
Removing them has no detectable compiler performance impact,
and it removes mutable shared state used by the backend.

Updates #15756

Change-Id: I2d2cf03f470f5eef5bcd50ff693ef6a01d481700
Reviewed-on: https://go-review.googlesource.com/38912
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -11,11 +11,17 @@ import (
 )
 
 func typeWithoutPointers() *Type {
-	return &Type{Etype: TSTRUCT, Extra: &StructType{Haspointers: 1}} // haspointers -> false
+	t := typ(TSTRUCT)
+	f := &Field{Type: typ(TINT)}
+	t.SetFields([]*Field{f})
+	return t
 }
 
 func typeWithPointers() *Type {
-	return &Type{Etype: TSTRUCT, Extra: &StructType{Haspointers: 2}} // haspointers -> true
+	t := typ(TSTRUCT)
+	f := &Field{Type: typ(TPTR64)}
+	t.SetFields([]*Field{f})
+	return t
 }
 
 // Test all code paths for cmpstackvarlt.

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

@@ -34,7 +34,7 @@ func TestSizeof(t *testing.T) {
 		{StructType{}, 12, 24},
 		{InterType{}, 4, 8},
 		{ChanType{}, 8, 16},
-		{ArrayType{}, 16, 24},
+		{ArrayType{}, 12, 16},
 		{InterMethType{}, 4, 8},
 		{DDDFieldType{}, 4, 8},
 		{FuncArgsType{}, 4, 8},

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

@@ -245,8 +245,7 @@ type StructType struct {
 	// Map links such structs back to their map type.
 	Map *Type
 
-	Funarg      Funarg // type of function arguments for arg struct
-	Haspointers uint8  // 0 unknown, 1 no, 2 yes
+	Funarg Funarg // type of function arguments for arg struct
 }
 
 // Fnstruct records the kind of function argument
@@ -304,9 +303,8 @@ func (t *Type) ChanType() *ChanType {
 
 // ArrayType contains Type fields specific to array types.
 type ArrayType struct {
-	Elem        *Type // element type
-	Bound       int64 // number of elements; <0 if unknown yet
-	Haspointers uint8 // 0 unknown, 1 no, 2 yes
+	Elem  *Type // element type
+	Bound int64 // number of elements; <0 if unknown yet
 }
 
 // SliceType contains Type fields specific to slice types.
@@ -1315,38 +1313,19 @@ func haspointers(t *Type) bool {
 		TUINT64, TUINTPTR, TFLOAT32, TFLOAT64, TCOMPLEX64, TCOMPLEX128, TBOOL:
 		return false
 
-	case TSLICE:
-		return true
-
 	case TARRAY:
-		at := t.Extra.(*ArrayType)
-		if at.Haspointers != 0 {
-			return at.Haspointers-1 != 0
+		if t.NumElem() == 0 { // empty array has no pointers
+			return false
 		}
-
-		ret := false
-		if t.NumElem() != 0 { // non-empty array
-			ret = haspointers(t.Elem())
-		}
-
-		at.Haspointers = 1 + uint8(obj.Bool2int(ret))
-		return ret
+		return haspointers(t.Elem())
 
 	case TSTRUCT:
-		st := t.StructType()
-		if st.Haspointers != 0 {
-			return st.Haspointers-1 != 0
-		}
-
-		ret := false
 		for _, t1 := range t.Fields().Slice() {
 			if haspointers(t1.Type) {
-				ret = true
-				break
+				return true
 			}
 		}
-		st.Haspointers = 1 + uint8(obj.Bool2int(ret))
-		return ret
+		return false
 	}
 
 	return true