cmd/compile: detect duplicate importing earlier

Change-Id: I05ba944e189a884b727e40a9526d212612c3e923
Reviewed-on: https://go-review.googlesource.com/c/go/+/299770
Trust: Keith Randall <khr@golang.org>
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/func.go

@@ -108,6 +108,9 @@ var inTypeCheckInl bool
 // Lazy typechecking of imported bodies. For local functions, CanInline will set ->typecheck
 // because they're a copy of an already checked body.
 func ImportedBody(fn *ir.Func) {
+	if fn.Inl.Body != nil {
+		return
+	}
 	lno := ir.SetPos(fn.Nname)
 
 	// When we load an inlined body, we need to allow OADDR
@@ -151,14 +154,6 @@ func ImportedBody(fn *ir.Func) {
 	inTypeCheckInl = false
 	ir.CurFunc = savefn
 
-	// During ImportBody (which imports fn.Func.Inl.Body),
-	// declarations are added to fn.Func.Dcl by funcBody(). Move them
-	// to fn.Func.Inl.Dcl for consistency with how local functions
-	// behave. (Append because ImportedBody may be called multiple
-	// times on same fn.)
-	fn.Inl.Dcl = append(fn.Inl.Dcl, fn.Dcl...)
-	fn.Dcl = nil
-
 	base.Pos = lno
 }
 

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

@@ -63,7 +63,7 @@ func expandDecl(n ir.Node) ir.Node {
 
 func ImportBody(fn *ir.Func) {
 	if fn.Inl.Body != nil {
-		return
+		base.Fatalf("%v already has inline body", fn)
 	}
 
 	r := importReaderFor(fn.Nname.Sym(), inlineImporter)