cmd/compile/internal/gc: skip autotmp vars in gc again

Instead of skipping them based on string matching much later in the
compilation process, skip them up front using the proper API.

Passes toolstash-check.

Change-Id: Ibd4c0448a0701ba0de3235d4689ef300235fa1d9
Reviewed-on: https://go-review.googlesource.com/37930
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -478,6 +478,10 @@ func debuginfo(fnsym *obj.LSym) []*dwarf.Var {
 			Gotype:  gotype,
 		})
 
+		if n.IsAutoTmp() {
+			continue
+		}
+
 		typename := dwarf.InfoPrefix + gotype.Name[len("type."):]
 		vars = append(vars, &dwarf.Var{
 			Name:   n.Sym.Name,

src/cmd/internal/dwarf/dwarf.go

@@ -7,10 +7,7 @@
 // this package contains the shared code.
 package dwarf
 
-import (
-	"fmt"
-	"strings"
-)
+import "fmt"
 
 // InfoPrefix is the prefix for all the symbols containing DWARF info entries.
 const InfoPrefix = "go.info."
@@ -576,9 +573,6 @@ 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 := range vars {
-		if strings.Contains(v.Name, ".autotmp_") {
-			continue
-		}
 		var n string
 		if names[v.Name] {
 			n = fmt.Sprintf("%s#%d", v.Name, len(names))