From 33deebea99048bd8b4019c0363b21f2c24267490 Mon Sep 17 00:00:00 2001
From: Martin Kinkelin <mkinkelin@symmetryinvestments.com>
Date: Sat, 29 Jul 2023 20:24:48 +0200
Subject: [PATCH] Symmetry: Make critical-path scheduler opt-in via --cp switch

---
 src/build.cc | 3 ++-
 src/build.h  | 6 ++++--
 src/ninja.cc | 8 +++++++-
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/build.cc b/src/build.cc
index 9c0dbc2d7e..b7e93fc845 100644
--- a/src/build.cc
+++ b/src/build.cc
@@ -795,7 +795,8 @@ bool Builder::AlreadyUpToDate() const {
 
 bool Builder::Build(string* err) {
   assert(!AlreadyUpToDate());
-  plan_.PrepareQueue(scan_.build_log());
+  plan_.PrepareQueue(config_.enable_critical_path_scheduler ? scan_.build_log()
+                                                            : NULL);
 
   status_->PlanHasTotalEdges(plan_.command_edge_count());
   int pending_commands = 0;
diff --git a/src/build.h b/src/build.h
index 7719d9a9a4..0cee9193b0 100644
--- a/src/build.h
+++ b/src/build.h
@@ -165,8 +165,9 @@ struct CommandRunner {
 
 /// Options (e.g. verbosity, parallelism) passed to a build.
 struct BuildConfig {
-  BuildConfig() : verbosity(NORMAL), dry_run(false), parallelism(1),
-                  failures_allowed(1), max_load_average(-0.0f) {}
+  BuildConfig()
+      : verbosity(NORMAL), dry_run(false), parallelism(1), failures_allowed(1),
+        max_load_average(-0.0f), enable_critical_path_scheduler(false) {}
 
   enum Verbosity {
     QUIET,  // No output -- used when testing.
@@ -182,6 +183,7 @@ struct BuildConfig {
   /// means that we do not have any limit.
   double max_load_average;
   DepfileParserOptions depfile_parser_options;
+  bool enable_critical_path_scheduler;
 };
 
 /// Builder wraps the build process: starting commands, updating status.
diff --git a/src/ninja.cc b/src/ninja.cc
index 2b71eb170f..d8445565ff 100644
--- a/src/ninja.cc
+++ b/src/ninja.cc
@@ -222,6 +222,8 @@ void Usage(const BuildConfig& config) {
 "  --version      print ninja version (\"%s\")\n"
 "  -v, --verbose  show all command lines while building\n"
 "  --quiet        don't show progress status, just command output\n"
+"  --cp           enable critical-path scheduler based on previous build times\n"
+"                 (schedule slowest targets first; may require huge peak RAM!)\n"
 "\n"
 "  -C DIR   change to DIR before doing anything else\n"
 "  -f FILE  specify input build file [default=build.ninja]\n"
@@ -1417,12 +1419,13 @@ int ReadFlags(int* argc, char*** argv,
               Options* options, BuildConfig* config) {
   DeferGuessParallelism deferGuessParallelism(config);
 
-  enum { OPT_VERSION = 1, OPT_QUIET = 2 };
+  enum { OPT_VERSION = 1, OPT_QUIET = 2, OPT_ENABLE_CP = 3 };
   const option kLongOptions[] = {
     { "help", no_argument, NULL, 'h' },
     { "version", no_argument, NULL, OPT_VERSION },
     { "verbose", no_argument, NULL, 'v' },
     { "quiet", no_argument, NULL, OPT_QUIET },
+    { "cp", no_argument, NULL, OPT_ENABLE_CP },
     { NULL, 0, NULL, 0 }
   };
 
@@ -1494,6 +1497,9 @@ int ReadFlags(int* argc, char*** argv,
       case OPT_VERSION:
         printf("%s\n", kNinjaVersion);
         return 0;
+      case OPT_ENABLE_CP:
+        config->enable_critical_path_scheduler = true;
+        break;
       case 'h':
       default:
         deferGuessParallelism.Refresh();