[release-branch.go1.9] cmd/compile: fix merge rules for panic calls

Use entire inlining call stack to decide whether two panic calls
can be merged. We used to merge panic calls when only the leaf
line numbers matched, but that leads to places higher up the call
stack being merged incorrectly.

Fixes #22083

Change-Id: Ia41400a80de4b6ecf3e5089abce0c42b65e9b38a
Reviewed-on: https://go-review.googlesource.com/67632
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-on: https://go-review.googlesource.com/70980
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

2 files changed, 43 insertions, 2 deletions

diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 9c1b3ca69f..63e9622983 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -282,7 +282,7 @@ type state struct {
 
 type funcLine struct {
 	f    *obj.LSym
-	file string
+	base *src.PosBase
 	line uint
 }
 
@@ -3456,7 +3456,7 @@ func (s *state) check(cmp *ssa.Value, fn *obj.LSym) {
 	bNext := s.f.NewBlock(ssa.BlockPlain)
 	line := s.peekPos()
 	pos := Ctxt.PosTable.Pos(line)
-	fl := funcLine{f: fn, file: pos.Filename(), line: pos.Line()}
+	fl := funcLine{f: fn, base: pos.Base(), line: pos.Line()}
 	bPanic := s.panics[fl]
 	if bPanic == nil {
 		bPanic = s.f.NewBlock(ssa.BlockPlain)
diff --git a/test/fixedbugs/issue22083.go b/test/fixedbugs/issue22083.go
new file mode 100644
index 0000000000..a385102d08
--- /dev/null
+++ b/test/fixedbugs/issue22083.go
@@ -0,0 +1,41 @@
+// run
+
+// Copyright 2017 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.
+
+// The compiler was panicking on the wrong line number, where
+// the panic was occurring in an inlined call.
+
+package main
+
+import (
+	"runtime/debug"
+	"strings"
+)
+
+type Wrapper struct {
+	a []int
+}
+
+func (w Wrapper) Get(i int) int {
+	return w.a[i]
+}
+
+func main() {
+	defer func() {
+		e := recover()
+		if e == nil {
+			panic("bounds check didn't fail")
+		}
+		stk := string(debug.Stack())
+		if !strings.Contains(stk, "issue22083.go:40") {
+			panic("wrong stack trace: " + stk)
+		}
+	}()
+	foo := Wrapper{a: []int{0, 1, 2}}
+	_ = foo.Get(0)
+	_ = foo.Get(1)
+	_ = foo.Get(2)
+	_ = foo.Get(3) // stack trace should mention this line
+}