[dev.regabi] cmd/compile: cleanup type-checking of defined types

The code for type-checking defined types was scattered between
typecheckdef, typecheckdeftype, and setUnderlying. There was redundant
work between them, and setUnderlying also needed to redo a lot of work
because of its brute-force solution of just copying all Type fields.

This CL reorders things so as many of the defined type's fields are
set in advance (in typecheckdeftype), and then setUnderlying only
copies over the details actually needed from the underlying type.

Incidentally, this evidently improves our error handling for an
existing test case, by allowing us to report an additional error.

Passes toolstash/buildall.

Change-Id: Id59a24341e7e960edd1f7366c3e2356da91b9fe7
Reviewed-on: https://go-review.googlesource.com/c/go/+/274432
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

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

@@ -3434,33 +3434,28 @@ func setUnderlying(t, underlying *types.Type) {
 		return
 	}
 
-	n := ir.AsNode(t.Nod)
 	ft := t.ForwardType()
-	cache := t.Cache
 
 	// TODO(mdempsky): Fix Type rekinding.
-	*t = *underlying
+	t.Etype = underlying.Etype
+	t.Extra = underlying.Extra
+	t.Width = underlying.Width
+	t.Align = underlying.Align
+	t.Orig = underlying.Orig
 
-	// Restore unnecessarily clobbered attributes.
+	if underlying.NotInHeap() {
-	t.Nod = n
+		t.SetNotInHeap(true)
-	t.Sym = n.Sym()
+	}
-	if n.Name() != nil {
+	if underlying.Broke() {
-		t.Vargen = n.Name().Vargen
+		t.SetBroke(true)
 	}
-	t.Cache = cache
-	t.SetDeferwidth(false)
 
 	// spec: "The declared type does not inherit any methods bound
 	// to the existing type, but the method set of an interface
 	// type [...] remains unchanged."
-	if !t.IsInterface() {
+	if t.IsInterface() {
-		*t.Methods() = types.Fields{}
+		*t.Methods() = *underlying.Methods()
-		*t.AllMethods() = types.Fields{}
+		*t.AllMethods() = *underlying.AllMethods()
-	}
-
-	// Propagate go:notinheap pragma from the Name to the Type.
-	if n.Name() != nil && n.Name().Pragma()&ir.NotInHeap != 0 {
-		t.SetNotInHeap(true)
 	}
 
 	// Update types waiting on this type.
@@ -3476,24 +3471,38 @@ func setUnderlying(t, underlying *types.Type) {
 	}
 }
 
-func typecheckdeftype(n ir.Node) {
+func typecheckdeftype(n *ir.Name) {
 	if enableTrace && base.Flag.LowerT {
 		defer tracePrint("typecheckdeftype", n)(nil)
 	}
 
+	t := types.New(types.TFORW)
+	t.Sym = n.Sym()
+	t.Vargen = n.Vargen
+	t.Nod = n
+	if n.Pragma()&ir.NotInHeap != 0 {
+		t.SetNotInHeap(true)
+	}
+
+	n.SetType(t)
 	n.SetTypecheck(1)
-	n.Name().Ntype = typecheckNtype(n.Name().Ntype)
+	n.SetWalkdef(1)
-	t := n.Name().Ntype.Type()
+
-	if t == nil {
+	defercheckwidth()
+	errorsBefore := base.Errors()
+	n.Ntype = typecheckNtype(n.Ntype)
+	if underlying := n.Ntype.Type(); underlying != nil {
+		setUnderlying(t, underlying)
+	} else {
 		n.SetDiag(true)
 		n.SetType(nil)
-	} else if n.Type() == nil {
-		n.SetDiag(true)
-	} else {
-		// copy new type and clear fields
-		// that don't come along.
-		setUnderlying(n.Type(), t)
 	}
+	if t.Etype == types.TFORW && base.Errors() > errorsBefore {
+		// Something went wrong during type-checking,
+		// but it was reported. Silence future errors.
+		t.SetBroke(true)
+	}
+	resumecheckwidth()
 }
 
 func typecheckdef(n ir.Node) {
@@ -3655,20 +3664,7 @@ func typecheckdef(n ir.Node) {
 		}
 
 		// regular type declaration
-		defercheckwidth()
-		n.SetWalkdef(1)
-		t := types.New(types.TFORW)
-		t.Nod = n
-		t.Sym = n.Sym()
-		n.SetType(t)
-		errorsBefore := base.Errors()
 		typecheckdeftype(n)
-		if n.Type().Etype == types.TFORW && base.Errors() > errorsBefore {
-			// Something went wrong during type-checking,
-			// but it was reported. Silence future errors.
-			n.Type().SetBroke(true)
-		}
-		resumecheckwidth()
 	}
 
 ret:

test/fixedbugs/issue28079b.go

@@ -13,5 +13,5 @@ import "unsafe"
 type T [uintptr(unsafe.Pointer(nil))]int // ERROR "non-constant array bound"
 
 func f() {
-	_ = complex(1<<uintptr(unsafe.Pointer(nil)), 0)
+	_ = complex(1<<uintptr(unsafe.Pointer(nil)), 0) // ERROR "shift of type float64"
 }