interceptor: store relative current directories

In one way or the other, the current directories of a command are always
relative to the root_dir. Hence, just make them relative at collection
time and remove this redundant information. This reduces the command log
of a kernel build by ~10%.

Signed-off-by: Matthias Maennich <maennich@google.com>
Change-Id: I6c4edb2a67b1d37a91e21e68d603876d96a64761

1 files changed, 25 insertions, 16 deletions

diff --git a/interceptor.cc b/interceptor.cc
index e9efccc..79f56e5 100644
--- a/interceptor.cc
+++ b/interceptor.cc
@@ -124,16 +124,17 @@ static std::optional<std::string> command_getenv(const Command& command, const c
   return {};
 }
 
-static bool default_make_relative(Command* command) {
+static std::optional<fs::path> command_get_root_directory(const Command& command) {
   // determine the ROOT_DIR
   fs::path root_directory;
-  if (const auto root = command_getenv(*command, kEnvRootDirectory)) {
-    root_directory = fs::path(*root) / "";
-  } else {
-    // there is no ROOT_DIR that we can use to make calls relative
-    return false;
+  if (const auto root = command_getenv(command, kEnvRootDirectory)) {
+    return fs::path(*root) / "";
   }
+  // there is no ROOT_DIR that we can use to make calls relative
+  return {};
+}
 
+static bool default_make_relative(Command* command, const fs::path& root_directory) {
   // determine the relative path to ROOT_DIR from the current working dir
   auto relative_root = fs::relative(root_directory) / "";
   if (relative_root == "./") {
@@ -146,8 +147,6 @@ static bool default_make_relative(Command* command) {
     return false;
   }
 
-  command->set_current_directory(fs::relative(command->current_directory(), root_directory));
-
   // replacement functor
   const auto replace_all = [&](auto& str) {
     size_t start = 0;
@@ -176,7 +175,7 @@ class Analyzer {
   virtual ~Analyzer() = default;
 
   void set_inputs_outputs(Command* command) const;
-  virtual bool make_relative(Command*) const { return false; }
+  virtual bool make_relative(Command*, const fs::path&) const { return false; }
   virtual bool should_recurse(Command*) const { return true; }
 
  protected:
@@ -243,7 +242,9 @@ class CompileLinkerAnalyzer : public Analyzer {
     return result;
   }
 
-  bool make_relative(Command* command) const final { return default_make_relative(command); }
+  bool make_relative(Command* command, const fs::path& root_directory) const final {
+    return default_make_relative(command, root_directory);
+  }
 
   // do not recurse the interceptor into the subprocesses of compilers/linkers;
   // otherwise we will trace (and get confused by) ld.lld/cc1-plus and friends.
@@ -268,7 +269,9 @@ class ArchiverAnalyzer : public Analyzer {
     return result;
   }
 
-  bool make_relative(Command* command) const final { return default_make_relative(command); }
+  bool make_relative(Command* command, const fs::path& root_directory) const final {
+    return default_make_relative(command, root_directory);
+  }
   bool should_recurse(Command*) const final { return false; }
 };
 
@@ -338,11 +341,17 @@ static std::optional<interceptor::Command> process_command(const char* filename,
 
   bool transformed = false;
 
-  // rewrite all command line arguments (including the program itself) to use
-  // paths relative to ROOT_DIR. This is essential for reproducible builds and
-  // furthermore necessary to produce cache hits in RBE.
-  if (command_getenv(command, kEnvMakeRelative)) {
-    transformed |= analyzer->make_relative(&command);
+  auto root_directory = command_get_root_directory(command);
+
+  if (root_directory.has_value()) {
+    command.set_current_directory(fs::relative(command.current_directory(), *root_directory));
+
+    // rewrite all command line arguments (including the program itself) to use
+    // paths relative to ROOT_DIR. This is essential for reproducible builds and
+    // furthermore necessary to produce cache hits in RBE.
+    if (command_getenv(command, kEnvMakeRelative)) {
+      transformed |= analyzer->make_relative(&command, *root_directory);
+    }
   }
 
   analyzer->set_inputs_outputs(&command);