From d6e2eb5d1fab5d912a2c97410d9ac66b1502c69a Mon Sep 17 00:00:00 2001
From: Mark Rousskov <mark.simulacrum@gmail.com>
Date: Fri, 28 Nov 2025 15:19:37 -0500
Subject: [PATCH] Reduce optimization level

Mostly trying to see what the delta in build time vs. runtime
performance is on our perf suite, I think it's unlikely we'd want to
land this.
---
 Cargo.toml                              | 3 +++
 src/bootstrap/src/core/builder/cargo.rs | 4 ++++
 2 files changed, 7 insertions(+)

diff --git a/Cargo.toml b/Cargo.toml
index 67c7a9d67edc8..1d19e3f8185b3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -59,6 +59,9 @@ exclude = [
   "obj",
 ]
 
+[profile.release]
+opt-level = 1
+
 [profile.release.package.rustc_thread_pool]
 # The rustc fork of Rayon has deadlock detection code which intermittently
 # causes overflows in the CI (see https://github.com/rust-lang/rust/issues/90227)
diff --git a/src/bootstrap/src/core/builder/cargo.rs b/src/bootstrap/src/core/builder/cargo.rs
index 093a754f1a4b7..f5e7d47c8d094 100644
--- a/src/bootstrap/src/core/builder/cargo.rs
+++ b/src/bootstrap/src/core/builder/cargo.rs
@@ -1387,6 +1387,10 @@ impl Builder<'_> {
             rustflags.arg("-Zmir_strip_debuginfo=locals-in-tiny-functions");
         }
 
+        if !matches!(mode, Mode::Std) {
+            cargo.env(cargo_profile_var("OPT_LEVEL", &self.config), "1");
+        }
+
         // take target-specific extra rustflags if any otherwise take `rust.rustflags`
         let extra_rustflags = self
             .config