cmd/dist: don't compile unneeded GOARCH SSA rewrite rules during bootstrap

Speeds up build (the bootstrap phase) by ~6 seconds.

Bootstrap goes from ~18 seconds to ~12 seconds.

Change-Id: I7e2ec8f5fc668bf6168d90098eaf70390b16e479
Reviewed-on: https://go-review.googlesource.com/40503
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

diff --git a/src/cmd/dist/buildtool.go b/src/cmd/dist/buildtool.go
index 015ee917b27b7e4e8244ddb7584e11a1a7315b55..cedd41457ddafbac8c67481f4d2e40dee5420914 100644 (file)
--- a/src/cmd/dist/buildtool.go
+++ b/src/cmd/dist/buildtool.go
@@ -12,7 +12,10 @@
 package main
 
 import (
+       "fmt"
        "os"
+       "path/filepath"
+       "runtime"
        "strings"
 )
 
@@ -123,9 +126,10 @@ func bootstrapBuildTools() {
                                }
                        }
                        srcFile := pathf("%s/%s", src, name)
+                       dstFile := pathf("%s/%s", dst, name)
                        text := readfile(srcFile)
-                       text = bootstrapFixImports(text, srcFile)
-                       writefile(text, pathf("%s/%s", dst, name), 0)
+                       text = bootstrapRewriteFile(text, srcFile)
+                       writefile(text, dstFile, 0)
                }
        }
 
@@ -158,7 +162,18 @@ func bootstrapBuildTools() {
        // https://groups.google.com/d/msg/golang-dev/Ss7mCKsvk8w/Gsq7VYI0AwAJ
        // Use the math_big_pure_go build tag to disable the assembly in math/big
        // which may contain unsupported instructions.
-       run(workspace, ShowOutput|CheckExit, pathf("%s/bin/go", goroot_bootstrap), "install", "-gcflags=-l", "-tags=math_big_pure_go", "-v", "bootstrap/cmd/...")
+       cmd := []string{
+               pathf("%s/bin/go", goroot_bootstrap),
+               "install",
+               "-gcflags=-l",
+               "-tags=math_big_pure_go",
+               "-v",
+       }
+       if tool := os.Getenv("GOBOOTSTRAP_TOOLEXEC"); tool != "" {
+               cmd = append(cmd, "-toolexec="+tool)
+       }
+       cmd = append(cmd, "bootstrap/cmd/...")
+       run(workspace, ShowOutput|CheckExit, cmd...)
 
        // Copy binaries into tool binary directory.
        for _, name := range bootstrapDirs {
@@ -174,6 +189,53 @@ func bootstrapBuildTools() {
        xprintf("\n")
 }
 
+var ssaRewriteFileSubstring = filepath.ToSlash("src/cmd/compile/internal/ssa/rewrite")
+
+// isUnneededSSARewriteFile reports whether srcFile is a
+// src/cmd/compile/internal/ssa/rewriteARCHNAME.go file for an
+// architecture that isn't for the current runtime.GOARCH.
+//
+// When unneeded is true archCaps is the rewrite base filename without
+// the "rewrite" prefix or ".go" suffix: AMD64, 386, ARM, ARM64, etc.
+func isUnneededSSARewriteFile(srcFile string) (archCaps string, unneeded bool) {
+       if !strings.Contains(srcFile, ssaRewriteFileSubstring) {
+               return "", false
+       }
+       fileArch := strings.TrimSuffix(strings.TrimPrefix(filepath.Base(srcFile), "rewrite"), ".go")
+       if fileArch == "" {
+               return "", false
+       }
+       b := fileArch[0]
+       if b == '_' || ('a' <= b && b <= 'z') {
+               return "", false
+       }
+       archCaps = fileArch
+       fileArch = strings.ToLower(fileArch)
+       if fileArch == strings.TrimSuffix(runtime.GOARCH, "le") {
+               return "", false
+       }
+       if fileArch == strings.TrimSuffix(os.Getenv("GOARCH"), "le") {
+               return "", false
+       }
+       return archCaps, true
+}
+
+func bootstrapRewriteFile(text, srcFile string) string {
+       // During bootstrap, generate dummy rewrite files for
+       // irrelevant architectures. We only need to build a bootstrap
+       // binary that works for the current runtime.GOARCH.
+       // This saves 6+ seconds of bootstrap.
+       if archCaps, ok := isUnneededSSARewriteFile(srcFile); ok {
+               return fmt.Sprintf(`package ssa
+
+func rewriteValue%s(v *Value) bool { panic("unused during bootstrap") }
+func rewriteBlock%s(b *Block) bool { panic("unused during bootstrap") }
+`, archCaps, archCaps)
+       }
+
+       return bootstrapFixImports(text, srcFile)
+}
+
 func bootstrapFixImports(text, srcFile string) string {
        lines := strings.SplitAfter(text, "\n")
        inBlock := false