// gocoverdir.
func upmergeCoverData(t *testing.T, gocoverdir string, mode string) {
	if testing.CoverMode() != mode {
		return
	}
	testGoCoverDir := os.Getenv("GOCOVERDIR")
	if testGoCoverDir == "" {
		return
	}
	args := []string{"tool", "covdata", "merge", "-pkg=runtime/coverage",
		"-o", testGoCoverDir, "-i", gocoverdir}

	}
	if len(ml) == 0 {
		fmt.Fprintf(os.Stderr, "program not built with -cover\n")
		return
	}

	goCoverDir = os.Getenv("GOCOVERDIR")
	if goCoverDir == "" {
		fmt.Fprintf(os.Stderr, "warning: GOCOVERDIR not set, no coverage data emitted\n")
		return
	}

	if err := emitMetaDataToDirectory(goCoverDir, ml); err != nil {
		fmt.Fprintf(os.Stderr, "error: coverage meta-data emit failed: %v\n", err)

		homeEnvName() + "=/no-home",
		"CCACHE_DISABLE=1", // ccache breaks with non-existent HOME
		"GOARCH=" + runtime.GOARCH,
		"TESTGO_GOHOSTARCH=" + goHostArch,
		"GOCACHE=" + testGOCACHE,
		"GOCOVERDIR=" + os.Getenv("GOCOVERDIR"),
		"GODEBUG=" + os.Getenv("GODEBUG"),
		"GOEXE=" + cfg.ExeSuffix,
		"GOEXPERIMENT=" + os.Getenv("GOEXPERIMENT"),
		"GOOS=" + runtime.GOOS,
		"TESTGO_GOHOSTOS=" + goHostOS,
		"GOPROXY=" + proxyURL,

			}
			for i := 0; i <= k; i++ {
				exepath := s.exepath1
				if m != 0 {
					exepath = s.exepath3
				}
				cmd := testenv.Command(t, exepath, args...)
				cmd.Env = append(cmd.Env, "GOCOVERDIR="+s.outdirs[m*2+k])
				b, err := cmd.CombinedOutput()
				if len(b) != 0 {
					t.Logf("## instrumented run output:\n%s", b)
				}
				if err != nil {
					t.Fatalf("instrumented run error: %v", err)
				}

	GOWASM
		For GOARCH=wasm, comma-separated list of experimental WebAssembly features to use.
		Valid values are satconv, signext.

Environment variables for use with code coverage:

	GOCOVERDIR
		Directory into which to write code coverage data files
		generated by running a "go build -cover" binary.
		Requires that GOEXPERIMENT=coverageredesign is enabled.

Special-purpose environment variables: