ci: Use multiple codegen units on non-dist bots

This commit is yet another attempt to bring down our cycle times by
parallelizing some of the long-and-serial parts of the build, for example
optimizing the libsyntax, librustc, and librustc_driver crate. The hope is that
any perf loss from codegen units is more than made up for with the perf gain
from using multiple codegen units.

The value of 8 codegen units here is pretty arbitrary, it's basically just a
number which hopefully means that the cores are always nice and warm. Also a
previous version of this commit bounced on Windows CI due to libstd being
compiled with multiple codegen units, so only the compiler is now compiled with
multiple codegen units.

config.toml.example

@@ -223,8 +223,10 @@
 
 # Number of codegen units to use for each compiler invocation. A value of 0
 # means "the number of cores on this machine", and 1+ is passed through to the
-# compiler.
+# compiler. The `codegen-units` setting applies to std/rustc/tools whereas
+# `rustc-codegen-units` does not apply to std
 #codegen-units = 1
+#rustc-codegen-units = 1
 
 # Whether or not debug assertions are enabled for the compiler and standard
 # library. Also enables compilation of debug! and trace! logging macros.

src/bootstrap/builder.rs

@@ -458,6 +458,12 @@ impl<'a> Builder<'a> {
             stage = compiler.stage;
         }
 
+        let cgus = if mode == Mode::Libstd {
+            self.config.rust_codegen_units
+        } else {
+            self.config.rustc_codegen_units.unwrap_or(self.config.rust_codegen_units)
+        };
+
         // Customize the compiler we're running. Specify the compiler to cargo
         // as our shim and then pass it some various options used to configure
         // how the actual compiler itself is called.
@@ -468,8 +474,7 @@ impl<'a> Builder<'a> {
              .env("RUSTC", self.out.join("bootstrap/debug/rustc"))
              .env("RUSTC_REAL", self.rustc(compiler))
              .env("RUSTC_STAGE", stage.to_string())
-             .env("RUSTC_CODEGEN_UNITS",
-                  self.config.rust_codegen_units.to_string())
+             .env("RUSTC_CODEGEN_UNITS", cgus.to_string())
              .env("RUSTC_DEBUG_ASSERTIONS",
                   self.config.rust_debug_assertions.to_string())
              .env("RUSTC_SYSROOT", self.sysroot(compiler))

src/bootstrap/config.rs

@@ -82,6 +82,7 @@ pub struct Config {
     // rust codegen options
     pub rust_optimize: bool,
     pub rust_codegen_units: u32,
+    pub rustc_codegen_units: Option<u32>,
     pub rust_debug_assertions: bool,
     pub rust_debuginfo: bool,
     pub rust_debuginfo_lines: bool,
@@ -254,6 +255,7 @@ impl Default for StringOrBool {
 struct Rust {
     optimize: Option<bool>,
     codegen_units: Option<u32>,
+    rustc_codegen_units: Option<u32>,
     debug_assertions: Option<bool>,
     debuginfo: Option<bool>,
     debuginfo_lines: Option<bool>,
@@ -472,6 +474,10 @@ impl Config {
                 Some(n) => config.rust_codegen_units = n,
                 None => {}
             }
+            match rust.rustc_codegen_units {
+                Some(0) => config.rustc_codegen_units = Some(num_cpus::get() as u32),
+                other => config.rustc_codegen_units = other,
+            }
         }
 
         if let Some(ref t) = toml.target {

src/bootstrap/configure.py

@@ -256,6 +256,8 @@ def set(key, value):
                 value = True
             elif keyval[1] == "false":
                 value = False
+            elif keyval[1].isdigit():
+                value = int(keyval[1])
             else:
                 value = keyval[1]
             set(keyval[0], value)
@@ -357,6 +359,8 @@ def to_toml(value):
         return '[' + ', '.join(map(to_toml, value)) + ']'
     elif isinstance(value, str):
         return "'" + value + "'"
+    elif isinstance(value, int):
+        return str(value)
     else:
         raise 'no toml'
 

src/ci/run.sh

@@ -52,6 +52,10 @@ if [ "$DEPLOY$DEPLOY_ALT" != "" ]; then
     RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --disable-llvm-assertions"
   fi
 else
+  # Let's try to take advantage of some of those sweet sweet parallelism wins by
+  # using multiple codegen units during the bootstrap
+  RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --set rust.rustc-codegen-units=8"
+
   # We almost always want debug assertions enabled, but sometimes this takes too
   # long for too little benefit, so we just turn them off.
   if [ "$NO_DEBUG_ASSERTIONS" = "" ]; then