cmd/compile/internal/types2: clean up asT converters (step 1 of 2)

This CL changes the convenience converters asT to use under instead
of optype. To make sure the effect is well understood, in a first
step, all asT functions are renamed to toT so that we can see which
call sites are affected. In almost all places, the change is what we
want. In some places we may get more conservative behavior (which is
easy to relax if need be). In some places (function calls through a
type parameter, append built-in) we now use singleUnder instead, for
a more general behavior, matching other primary expressions or built-
ins.

This change removes the last use of optype and thus also theTop and
top, all of which have been deleted from the code.

The next CL renames the toT converters back to their asT form.

Change-Id: I35d1ad866ce46de175a055b36ef577d99bb9de22
Reviewed-on: https://go-review.googlesource.com/c/go/+/358597
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

1 files changed, 3 insertions, 7 deletions

diff --git a/src/cmd/compile/internal/types2/predicates.go b/src/cmd/compile/internal/types2/predicates.go
index 74ad3da72c..f89575b24c 100644
--- a/src/cmd/compile/internal/types2/predicates.go
+++ b/src/cmd/compile/internal/types2/predicates.go
@@ -56,7 +56,7 @@ func isNumericOrString(typ Type) bool { return is(typ, IsNumeric|IsString) }
 // are not fully set up.
 func isTyped(typ Type) bool {
 	// isTyped is called with types that are not fully
-	// set up. Must not call asBasic()!
+	// set up. Must not call toBasic()!
 	t, _ := typ.(*Basic)
 	return t == nil || t.info&IsUntyped == 0
 }
@@ -70,13 +70,13 @@ func isOrdered(typ Type) bool { return is(typ, IsOrdered) }
 
 func isConstType(typ Type) bool {
 	// Type parameters are never const types.
-	t, _ := under(typ).(*Basic)
+	t := toBasic(typ)
 	return t != nil && t.info&IsConstType != 0
 }
 
 // IsInterface reports whether typ is an interface type.
 func IsInterface(typ Type) bool {
-	return asInterface(typ) != nil
+	return toInterface(typ) != nil
 }
 
 // Comparable reports whether values of type T are comparable.
@@ -339,10 +339,6 @@ func identical(x, y Type, cmpTags bool, p *ifacePair) bool {
 	case *TypeParam:
 		// nothing to do (x and y being equal is caught in the very beginning of this function)
 
-	case *top:
-		// Either both types are theTop in which case the initial x == y check
-		// will have caught them. Otherwise they are not identical.
-
 	case nil:
 		// avoid a crash in case of nil type