From 2adf26fc72f354aabd65da176eb9f8806b0d2ef2 Mon Sep 17 00:00:00 2001
From: clubby789 <jamie@hill-daniel.co.uk>
Date: Mon, 23 Jan 2023 21:21:35 +0000
Subject: [PATCH] Add `rust.lto=off` to bootstrap

---
 config.toml.example                         |  3 ++-
 src/bootstrap/compile.rs                    | 10 ++++++++++
 src/bootstrap/config.rs                     |  4 +++-
 src/bootstrap/defaults/config.compiler.toml |  2 ++
 src/bootstrap/defaults/config.library.toml  |  2 ++
 5 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/config.toml.example b/config.toml.example
index 5e1d2f2e314ff..e0f02eac9c34b 100644
--- a/config.toml.example
+++ b/config.toml.example
@@ -646,7 +646,8 @@ changelog-seen = 2
 
 # Select LTO mode that will be used for compiling rustc. By default, thin local LTO
 # (LTO within a single crate) is used (like for any Rust crate). You can also select
-# "thin" or "fat" to apply Thin/Fat LTO to the `rustc_driver` dylib.
+# "thin" or "fat" to apply Thin/Fat LTO to the `rustc_driver` dylib, or "off" to disable
+# LTO entirely.
 #lto = "thin-local"
 
 # =============================================================================
diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index 68d1db0160a2e..07c0d2233caeb 100644
--- a/src/bootstrap/compile.rs
+++ b/src/bootstrap/compile.rs
@@ -379,6 +379,9 @@ pub fn std_cargo(builder: &Builder<'_>, target: TargetSelection, stage: u32, car
     if stage >= 1 {
         cargo.rustflag("-Cembed-bitcode=yes");
     }
+    if builder.config.rust_lto == RustcLto::Off {
+        cargo.rustflag("-Clto=off");
+    }
 
     // By default, rustc does not include unwind tables unless they are required
     // for a particular target. They are not required by RISC-V targets, but
@@ -722,6 +725,13 @@ impl Step for Rustc {
                     cargo.rustflag("-Cembed-bitcode=yes");
                 }
                 RustcLto::ThinLocal => { /* Do nothing, this is the default */ }
+                RustcLto::Off => {
+                    cargo.rustflag("-Clto=off");
+                }
+            }
+        } else {
+            if builder.config.rust_lto == RustcLto::Off {
+                cargo.rustflag("-Clto=off");
             }
         }
 
diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index b41d60d51a8b5..a28fe612deb7a 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -332,8 +332,9 @@ impl SplitDebuginfo {
 }
 
 /// LTO mode used for compiling rustc itself.
-#[derive(Default, Clone)]
+#[derive(Default, Clone, PartialEq)]
 pub enum RustcLto {
+    Off,
     #[default]
     ThinLocal,
     Thin,
@@ -348,6 +349,7 @@ impl std::str::FromStr for RustcLto {
             "thin-local" => Ok(RustcLto::ThinLocal),
             "thin" => Ok(RustcLto::Thin),
             "fat" => Ok(RustcLto::Fat),
+            "off" => Ok(RustcLto::Off),
             _ => Err(format!("Invalid value for rustc LTO: {}", s)),
         }
     }
diff --git a/src/bootstrap/defaults/config.compiler.toml b/src/bootstrap/defaults/config.compiler.toml
index 2f4ccb825c4d8..b98b13119e8ad 100644
--- a/src/bootstrap/defaults/config.compiler.toml
+++ b/src/bootstrap/defaults/config.compiler.toml
@@ -12,6 +12,8 @@ debug-logging = true
 incremental = true
 # Print backtrace on internal compiler errors during bootstrap
 backtrace-on-ice = true
+# Make the compiler and standard library faster to build, at the expense of a ~20% runtime slowdown.
+lto = "off"
 
 [llvm]
 # Will download LLVM from CI if available on your platform.
diff --git a/src/bootstrap/defaults/config.library.toml b/src/bootstrap/defaults/config.library.toml
index 7bc054d3a49fc..f362c4111f107 100644
--- a/src/bootstrap/defaults/config.library.toml
+++ b/src/bootstrap/defaults/config.library.toml
@@ -8,6 +8,8 @@ bench-stage = 0
 [rust]
 # This greatly increases the speed of rebuilds, especially when there are only minor changes. However, it makes the initial build slightly slower.
 incremental = true
+# Make the compiler and standard library faster to build, at the expense of a ~20% runtime slowdown.
+lto = "off"
 
 [llvm]
 # Will download LLVM from CI if available on your platform.