cmd/compile: add up-to-date test for generated files

This runs the ssa/_gen generator writing files into
a temporary directory, and then checks that there are
no differences with what is currently in the ssa directory,
and also checks that any file with the "generated from
_gen/..." header was actually generated, and checks that
the headers on the generated file match the expected
header prefix.

Change-Id: Ic8eeb0b06cf6f2e576a013e865b331a12d3a77aa
Reviewed-on: https://go-review.googlesource.com/c/go/+/680615
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>

Author: dr2chase

src/cmd/compile/internal/ssa/_gen/README

@@ -9,3 +9,8 @@ more information.
 
 To regenerate everything, run "go generate" on the ssa package
 in the parent directory.
+
+The parent directory contains a test in generate_test.go that will fail
+if the generated files are not up-to-date, and to allow that test to
+run in no-network environments, golang.org/x/tools/go/ast/astutil is
+vendored.

src/cmd/compile/internal/ssa/_gen/allocators.go

@@ -155,7 +155,7 @@ func genAllocators() {
 		panic(err)
 	}
 
-	if err := os.WriteFile("../allocators.go", b, 0666); err != nil {
+	if err := os.WriteFile(outFile("allocators.go"), b, 0666); err != nil {
 		log.Fatalf("can't write output: %v\n", err)
 	}
 }

src/cmd/compile/internal/ssa/_gen/main.go

@@ -113,6 +113,7 @@ var archs []arch
 var cpuprofile = flag.String("cpuprofile", "", "write cpu profile to `file`")
 var memprofile = flag.String("memprofile", "", "write memory profile to `file`")
 var tracefile = flag.String("trace", "", "write trace to `file`")
+var outDir = flag.String("outdir", "..", "directory in which to write generated files")
 
 func main() {
 	flag.Parse()
@@ -144,6 +145,13 @@ func main() {
 		defer trace.Stop()
 	}
 
+	if *outDir != ".." {
+		err := os.MkdirAll(*outDir, 0755)
+		if err != nil {
+			log.Fatalf("failed to create output directory: %v", err)
+		}
+	}
+
 	slices.SortFunc(archs, func(a, b arch) int {
 		return strings.Compare(a.name, b.name)
 	})
@@ -193,6 +201,10 @@ func main() {
 	}
 }
 
+func outFile(file string) string {
+	return *outDir + "/" + file
+}
+
 func genOp() {
 	w := new(bytes.Buffer)
 	fmt.Fprintf(w, "// Code generated from _gen/*Ops.go using 'go generate'; DO NOT EDIT.\n")
@@ -500,7 +512,7 @@ func genOp() {
 		panic(err)
 	}
 
-	if err := os.WriteFile("../opGen.go", b, 0666); err != nil {
+	if err := os.WriteFile(outFile("opGen.go"), b, 0666); err != nil {
 		log.Fatalf("can't write output: %v\n", err)
 	}
 

src/cmd/compile/internal/ssa/_gen/rulegen.go

@@ -322,7 +322,7 @@ func genRulesSuffix(arch arch, suff string) {
 	file = astutil.Apply(file, pre, post).(*ast.File)
 
 	// Write the well-formatted source to file
-	f, err := os.Create("../rewrite" + arch.name + suff + ".go")
+	f, err := os.Create(outFile("rewrite" + arch.name + suff + ".go"))
 	if err != nil {
 		log.Fatalf("can't write output: %v", err)
 	}