cmd/compile: make Class a Stringer

Change-Id: I7fd137d01ab5a0690773ca6e47d2bd796f0e393e
Reviewed-on: https://go-review.googlesource.com/42177
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

+// Code generated by "stringer -type=Class"; DO NOT EDIT.
+
+package gc
+
+import "fmt"
+
+const _Class_name = "PxxxPEXTERNPAUTOPAUTOHEAPPPARAMPPARAMOUTPFUNCPDISCARD"
+
+var _Class_index = [...]uint8{0, 4, 11, 16, 25, 31, 40, 45, 53}
+
+func (i Class) String() string {
+	if i >= Class(len(_Class_index)-1) {
+		return fmt.Sprintf("Class(%d)", i)
+	}
+	return _Class_name[_Class_index[i]:_Class_index[i+1]]
+}

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

@@ -31,6 +31,7 @@ func isRuntimePkg(p *types.Pkg) bool {
 // called declaration contexts.
 type Class uint8
 
+//go:generate stringer -type=Class
 const (
 	Pxxx      Class = iota // no class; used during ssa conversion to indicate pseudo-variables
 	PEXTERN                // global variable