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

@@ -246,7 +246,6 @@ type StructType struct {
 	Map *Type
 
 	Funarg Funarg // type of function arguments for arg struct
-	Haspointers uint8  // 0 unknown, 1 no, 2 yes
 }
 
 // Fnstruct records the kind of function argument
@@ -306,7 +305,6 @@ func (t *Type) ChanType() *ChanType {
 type ArrayType struct {
 	Elem  *Type // element type
 	Bound int64 // number of elements; <0 if unknown yet
-	Haspointers uint8 // 0 unknown, 1 no, 2 yes
 }
 
 // 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
-		}
-
-		ret := false
-		if t.NumElem() != 0 { // non-empty array
-			ret = haspointers(t.Elem())
+		if t.NumElem() == 0 { // empty array has no pointers
+			return false
 		}
-
-		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