Extend duplicate check to exported wrappers

Change-Id: I892fca0a374476aa9e65bf26fb03b73d6a0ae75a
Reviewed-on: https://go-review.googlesource.com/1583
Reviewed-by: Robert Griesemer <gri@golang.org>

go/ssa/func.go

@@ -464,7 +464,10 @@ func (f *Function) emit(instr Instruction) Value {
 // (i.e. from == f.Pkg.Object), they are rendered without the package path.
 // For example: "IsNaN", "(*Buffer).Bytes", etc.
 //
-// Invariant: all non-synthetic functions have distinct package-qualified names.
+// All non-synthetic functions have distinct package-qualified names.
+// (But two methods may have the same name "(T).f" if one is a synthetic
+// wrapper promoting a non-exported method "f" from another package; in
+// that case, the strings are equal but the identifiers "f" are distinct.)
 //
 func (f *Function) RelString(from *types.Package) string {
 	// Anonymous?

go/ssa/stdlib_test.go

@@ -10,6 +10,7 @@ package ssa_test
 // Run with "go test -cpu=8 to" set GOMAXPROCS.
 
 import (
+	"go/ast"
 	"go/build"
 	"go/token"
 	"runtime"
@@ -82,9 +83,11 @@ func TestStdlib(t *testing.T) {
 	allFuncs := ssautil.AllFunctions(prog)
 
 	// Check that all non-synthetic functions have distinct names.
+	// Synthetic wrappers for exported methods should be distinct too,
+	// except for unexported ones (explained at (*Function).RelString).
 	byName := make(map[string]*ssa.Function)
 	for fn := range allFuncs {
-		if fn.Synthetic == "" {
+		if fn.Synthetic == "" || ast.IsExported(fn.Name()) {
 			str := fn.String()
 			prev := byName[str]
 			byName[str] = fn