cmd/compile: make a better bogus line for empty infinite loops
The old recipe for making an infinite loop not be infinite
in the debugger could create an instruction (Prog) with a
line number not tied to any file (index == 0). This caused
downstream failures in DWARF processing.
So don't do that. Also adds a test, also adds a check+panic
to ensure that the next time this happens the error is less
mystifying.
Fixes #35652
Change-Id: I04f30bc94fdc4aef20dd9130561303ff84fd945e
Reviewed-on: https://go-review.googlesource.com/c/go/+/207613
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index fa4fd05..96fbddb 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -6041,6 +6041,9 @@
if s.bstart[b.ID] == s.pp.next && len(b.Succs) == 1 && b.Succs[0].Block() == b {
p := thearch.Ginsnop(s.pp)
p.Pos = p.Pos.WithIsStmt()
+ if b.Pos == src.NoXPos {
+ b.Pos = p.Pos // It needs a file, otherwise a no-file non-zero line causes confusion. See #35652.
+ }
b.Pos = b.Pos.WithBogusLine() // Debuggers are not good about infinite loops, force a change in line number
}
// Emit control flow instructions for block
diff --git a/src/cmd/internal/src/xpos.go b/src/cmd/internal/src/xpos.go
index 54fe64c..23c8346 100644
--- a/src/cmd/internal/src/xpos.go
+++ b/src/cmd/internal/src/xpos.go
@@ -71,6 +71,10 @@
// gdb chooses not to display the bogus line; delve shows it with a complaint, but the
// alternative behavior is to hang.
func (p XPos) WithBogusLine() XPos {
+ if p.index == 0 {
+ // See #35652
+ panic("Assigning a bogus line to XPos with no file will cause mysterious downstream failures.")
+ }
p.lico = makeBogusLico()
return p
}
diff --git a/test/fixedbugs/issue35652.go b/test/fixedbugs/issue35652.go
new file mode 100644
index 0000000..1ae4069
--- /dev/null
+++ b/test/fixedbugs/issue35652.go
@@ -0,0 +1,15 @@
+// compile
+
+// Copyright 2019 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.
+
+package p
+
+func f() {
+ for true {
+ if true {
+ continue
+ }
+ }
+}
