cmd/compile: handle degenerate entry blocks in -N debug gen

The code that created DWARF debug var locations for input parameters
in the non-optimized case for regabi was not doing the right thing for
degenerate functions with infinite loops. Detect these cases and don't
try to emit the normal location data.

Fixes #45948.

Change-Id: I2717fc4bac2e03d5d850a6ec8a09ed05fed0c896
Reviewed-on: https://go-review.googlesource.com/c/go/+/316752
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/test/fixedbugs/issue45948.go b/test/fixedbugs/issue45948.go
new file mode 100644
index 0000000000..37f8e70e2b
--- /dev/null
+++ b/test/fixedbugs/issue45948.go
@@ -0,0 +1,16 @@
+// compile -N
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 45948: assert in debug generation for degenerate
+// function with infinite loop.
+
+package p
+
+func f(p int) {
+L:
+	goto L
+
+}