cmd/compile: ensure necessary types appear in .debug_info

Autotmp filtering was too aggressive and excluded types
necessary to make debuggers work properly.  Restore the
"late filter" in dwarf.go based on names to exclude autotmps,
and remove the "early filter" in pgen.go based on how the
name was introduced.  However, the updated naming scheme
with a dot prefix is retained to prevent accidental clashes
with legal Go identifier names.

Includes test (grouped with runtime gdb tests),
verified to fail without the fix.

Updates #17644.
Fixes #17830.

Change-Id: I7ec3f7230083889660236e5f6bc77ba5fe434e93
Reviewed-on: https://go-review.googlesource.com/33233
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/pgen.go

@@ -427,9 +427,8 @@ func compile(fn *Node) {
 			}
 			fallthrough
 		case PPARAM, PPARAMOUT:
-			if n.IsAutoTmp() { // skip debugging info for temporaries
-				continue
-			}
+			// The symbol is excluded later from debugging info if its name begins ".autotmp_", but the type is still necessary.
+			// See bugs #17644 and #17830 and cmd/internal/dwarf/dwarf.go
 			p := Gins(obj.ATYPE, n, nil)
 			p.From.Sym = obj.Linklookup(Ctxt, n.Sym.Name, 0)
 			p.To.Type = obj.TYPE_MEM

src/cmd/internal/dwarf/dwarf.go

@@ -9,6 +9,7 @@ package dwarf
 
 import (
 	"fmt"
+	"strings"
 )
 
 // InfoPrefix is the prefix for all the symbols containing DWARF info entries.
@@ -576,6 +577,9 @@ func PutFunc(ctxt Context, s Sym, name string, external bool, startPC Sym, size
 	putattr(ctxt, s, DW_ABRV_FUNCTION, DW_FORM_flag, DW_CLS_FLAG, ev, 0)
 	names := make(map[string]bool)
 	for v := vars; v != nil; v = v.Link {
+		if strings.Contains(v.Name, ".autotmp_") {
+			continue
+		}
 		var n string
 		if names[v.Name] {
 			n = fmt.Sprintf("%s#%d", v.Name, len(names))

src/runtime/runtime-gdb_test.go

@@ -15,6 +15,7 @@ import (
 	"regexp"
 	"runtime"
 	"strconv"
+	"strings"
 	"testing"
 )
 
@@ -275,3 +276,72 @@ func TestGdbBacktrace(t *testing.T) {
 		}
 	}
 }
+
+const autotmpTypeSource = `
+package main
+
+type astruct struct {
+	a, b int
+}
+
+func main() {
+	var iface interface{} = map[string]astruct{}
+	var iface2 interface{} = []astruct{}
+	println(iface, iface2)
+}
+`
+
+// TestGdbAutotmpTypes ensures that types of autotmp variables appear in .debug_info
+// See bug #17830.
+func TestGdbAutotmpTypes(t *testing.T) {
+	t.Parallel()
+	checkGdbEnvironment(t)
+	checkGdbVersion(t)
+
+	dir, err := ioutil.TempDir("", "go-build")
+	if err != nil {
+		t.Fatalf("failed to create temp directory: %v", err)
+	}
+	defer os.RemoveAll(dir)
+
+	// Build the source code.
+	src := filepath.Join(dir, "main.go")
+	err = ioutil.WriteFile(src, []byte(autotmpTypeSource), 0644)
+	if err != nil {
+		t.Fatalf("failed to create file: %v", err)
+	}
+	cmd := exec.Command(testenv.GoToolPath(t), "build", "-gcflags=-N -l", "-o", "a.exe")
+	cmd.Dir = dir
+	out, err := testEnv(cmd).CombinedOutput()
+	if err != nil {
+		t.Fatalf("building source %v\n%s", err, out)
+	}
+
+	// Execute gdb commands.
+	args := []string{"-nx", "-batch",
+		"-ex", "set startup-with-shell off",
+		"-ex", "break main.main",
+		"-ex", "run",
+		"-ex", "step",
+		"-ex", "info types astruct",
+		filepath.Join(dir, "a.exe"),
+	}
+	got, _ := exec.Command("gdb", args...).CombinedOutput()
+
+	sgot := string(got)
+
+	// Check that the backtrace matches the source code.
+	types := []string{
+		"struct []main.astruct;",
+		"struct bucket<string,main.astruct>;",
+		"struct hash<string,main.astruct>;",
+		"struct main.astruct;",
+		"typedef struct hash<string,main.astruct> * map[string]main.astruct;",
+	}
+	for _, name := range types {
+		if !strings.Contains(sgot, name) {
+			t.Errorf("could not find %s in 'info typrs astruct' output", name)
+			t.Fatalf("gdb output:\n%v", sgot)
+		}
+	}
+}