test/run: use go tool compile + link instead of go run when possible

This cuts 6 seconds off all.bash with the new go command.
Not a ton, but also an easy 6 seconds to grab.

The -tags=use_go_run in the misc/cgo tests is just some
go command flag that will make run.go use go run,
but without making everything look stale.
(Those tests have relative imports,
so go tool compile+link is not enough.)

Change-Id: I43bf4bb661d3adde2b2d4aad5e8f64b97bc69ba9
Reviewed-on: https://go-review.googlesource.com/73994Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/life/main.go

-// cmpout
+// cmpout -tags=use_go_run
 
 // Copyright 2010 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -11,9 +11,10 @@
 package main
 
 import (
-	"."
 	"flag"
 	"fmt"
+
+	"."
 )
 
 const MAXDIM = 100

misc/cgo/stdio/chain.go

-// cmpout
+// cmpout -tags=use_go_run
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style

misc/cgo/stdio/fib.go

-// cmpout
+// cmpout -tags=use_go_run
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style

misc/cgo/stdio/hello.go

-// cmpout
+// cmpout -tags=use_go_run
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style

test/run.go

@@ -799,13 +799,38 @@ func (t *test) run() {
 
 	case "run":
 		useTmp = false
-		cmd := []string{"go", "run", goGcflags()}
-		if *linkshared {
-			cmd = append(cmd, "-linkshared")
+		var out []byte
+		var err error
+		if len(flags)+len(args) == 0 && goGcflags() == "" && !*linkshared {
+			// If we're not using special go command flags,
+			// skip all the go command machinery.
+			// This avoids any time the go command would
+			// spend checking whether, for example, the installed
+			// package runtime is up to date.
+			// Because we run lots of trivial test programs,
+			// the time adds up.
+			pkg := filepath.Join(t.tempDir, "pkg.a")
+			if _, err := runcmd("go", "tool", "compile", "-o", pkg, t.goFileName()); err != nil {
+				t.err = err
+				return
+			}
+			exe := filepath.Join(t.tempDir, "test.exe")
+			cmd := []string{"go", "tool", "link", "-s", "-w"}
+			cmd = append(cmd, "-o", exe, pkg)
+			if _, err := runcmd(cmd...); err != nil {
+				t.err = err
+				return
+			}
+			out, err = runcmd(append([]string{exe}, args...)...)
+		} else {
+			cmd := []string{"go", "run", goGcflags()}
+			if *linkshared {
+				cmd = append(cmd, "-linkshared")
+			}
+			cmd = append(cmd, flags...)
+			cmd = append(cmd, t.goFileName())
+			out, err = runcmd(append(cmd, args...)...)
 		}
-		cmd = append(cmd, flags...)
-		cmd = append(cmd, t.goFileName())
-		out, err := runcmd(append(cmd, args...)...)
 		if err != nil {
 			t.err = err
 			return