[dev.typeparams] cmd/compile: make all pointer types have the same shape

Except unsafe.Pointer. It has a different Kind, which makes it trickier.

Change-Id: I12582afb6e591bea35da9e43ac8d141ed19532a3
Reviewed-on: https://go-review.googlesource.com/c/go/+/338749
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

src/cmd/compile/internal/typecheck/subr.go

@@ -1351,6 +1351,12 @@ func Shapify(t *types.Type) *types.Type {
 	// Map all types with the same underlying type to the same shape.
 	u := t.Underlying()
 
+	// All pointers have the same shape.
+	// TODO: Make unsafe.Pointer the same shape as normal pointers.
+	if u.Kind() == types.TPTR {
+		u = types.Types[types.TUINT8].PtrTo()
+	}
+
 	if s := shaped[u]; s != nil {
 		return s //TODO: keep?
 	}

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

@@ -31,7 +31,7 @@ func identical(t1, t2 *Type, cmpTags bool, assumedEqual map[typePair]struct{}) b
 	if t1.sym != nil || t2.sym != nil {
 		if t1.HasShape() || t2.HasShape() {
 			switch t1.kind {
-			case TINT8, TUINT8, TINT16, TUINT16, TINT32, TUINT32, TINT64, TUINT64, TINT, TUINT, TUINTPTR, TCOMPLEX64, TCOMPLEX128, TFLOAT32, TFLOAT64, TBOOL, TSTRING, TUNSAFEPTR:
+			case TINT8, TUINT8, TINT16, TUINT16, TINT32, TUINT32, TINT64, TUINT64, TINT, TUINT, TUINTPTR, TCOMPLEX64, TCOMPLEX128, TFLOAT32, TFLOAT64, TBOOL, TSTRING, TPTR, TUNSAFEPTR:
 				return true
 			}
 			// fall through to unnamed type comparison for complex types.

test/typeparam/shape1.go

@@ -10,7 +10,8 @@ type I interface {
 	foo() int
 }
 
-// There should be a single instantiation of f in this program.
+// There should be one instantiation of f for both squarer and doubler.
+// Similarly, there should be one instantiation of f for both *incrementer and *decrementer.
 func f[T I](x T) int {
 	return x.foo()
 }
@@ -27,7 +28,23 @@ func (x doubler) foo() int {
 	return int(2*x)
 }
 
+type incrementer int16
+
+func (x *incrementer) foo() int {
+	return int(*x+1)
+}
+
+type decrementer int32
+
+func (x *decrementer) foo() int{
+	return int(*x-1)
+}
+
 func main() {
 	println(f(squarer(5)))
 	println(f(doubler(5)))
+	var i incrementer = 5
+	println(f(&i))
+	var d decrementer = 5
+	println(f(&d))
 }

test/typeparam/shape1.out

@@ -1,2 +1,4 @@
 25
 10
+6
+4