cmd/compile: check for iteration after range func loop exit

When this happens, panic.

This is a revised version of a check that used #next,
where this one instead uses a per-loop #exit flag,
and catches more problematic iterators.

Updates #56413.
Updates #61405.

Change-Id: I6574f754e475bb67b9236b4f6c25979089f9b629
Reviewed-on: https://go-review.googlesource.com/c/go/+/540263
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

3 files changed, 14 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/noder/codes.go b/src/cmd/compile/internal/noder/codes.go
index 88c10a74e7..8bdbfc9a88 100644
--- a/src/cmd/compile/internal/noder/codes.go
+++ b/src/cmd/compile/internal/noder/codes.go
@@ -62,6 +62,7 @@ const (
 	exprFuncInst
 	exprRecv
 	exprReshape
+	exprRuntimeBuiltin // a reference to a runtime function from transformed syntax. Followed by string name, e.g., "panicrangeexit"
 )
 
 type codeAssign int
diff --git a/src/cmd/compile/internal/noder/reader.go b/src/cmd/compile/internal/noder/reader.go
index 3cd7b7c683..b4c2801e53 100644
--- a/src/cmd/compile/internal/noder/reader.go
+++ b/src/cmd/compile/internal/noder/reader.go
@@ -2442,6 +2442,10 @@ func (r *reader) expr() (res ir.Node) {
 			n.SetTypecheck(1)
 		}
 		return n
+
+	case exprRuntimeBuiltin:
+		builtin := typecheck.LookupRuntime(r.String())
+		return builtin
 	}
 }
 
diff --git a/src/cmd/compile/internal/noder/writer.go b/src/cmd/compile/internal/noder/writer.go
index ddbe2f84e4..46d5213694 100644
--- a/src/cmd/compile/internal/noder/writer.go
+++ b/src/cmd/compile/internal/noder/writer.go
@@ -1715,6 +1715,15 @@ func (w *writer) expr(expr syntax.Expr) {
 	targs := inst.TypeArgs
 
 	if tv, ok := w.p.maybeTypeAndValue(expr); ok {
+		if tv.IsRuntimeHelper() {
+			if pkg := obj.Pkg(); pkg != nil && pkg.Name() == "runtime" {
+				objName := obj.Name()
+				w.Code(exprRuntimeBuiltin)
+				w.String(objName)
+				return
+			}
+		}
+
 		if tv.IsType() {
 			w.p.fatalf(expr, "unexpected type expression %v", syntax.String(expr))
 		}