Auto merge of #146765 - Zalathar:rollup-ewh4s9o, r=Zalathar

Rollup of 10 pull requests

Successful merges:

 - rust-lang/rust#146229 (Automatically switch to lto-fat when flag RUSTFLAGS="- Zautodiff=Enable" is set)
 - rust-lang/rust#146484 (rustdoc-search: JavaScript optimization based on Firefox Profiler output)
 - rust-lang/rust#146541 (std: simplify host lookup)
 - rust-lang/rust#146615 (rustc_codegen_llvm: Feature Conversion Tidying)
 - rust-lang/rust#146638 (`rustc_next_trait_solver`: canonical out of `EvalCtxt`)
 - rust-lang/rust#146663 (Allow windows resource compiler to be overridden)
 - rust-lang/rust#146691 (std: Fix WASI implementation of `remove_dir_all`)
 - rust-lang/rust#146709 (stdarch subtree update)
 - rust-lang/rust#146738 (Fix tidy spellchecking on Windows)
 - rust-lang/rust#146740 (miri subtree update)

r? `@ghost`
`@rustbot` modify labels: rollup

2 files changed, 12 insertions, 0 deletions

diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 297df7c2c97..795cb2b2cfe 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -1509,6 +1509,11 @@ impl Options {
     pub fn get_symbol_mangling_version(&self) -> SymbolManglingVersion {
         self.cg.symbol_mangling_version.unwrap_or(SymbolManglingVersion::Legacy)
     }
+
+    #[inline]
+    pub fn autodiff_enabled(&self) -> bool {
+        self.unstable_opts.autodiff.contains(&AutoDiff::Enable)
+    }
 }
 
 impl UnstableOptions {
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 3525c7c1d1a..d0dd2cdac0c 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -600,6 +600,13 @@ impl Session {
 
     /// Calculates the flavor of LTO to use for this compilation.
     pub fn lto(&self) -> config::Lto {
+        // Autodiff currently requires fat-lto to have access to the llvm-ir of all (indirectly) used functions and types.
+        // fat-lto is the easiest solution to this requirement, but quite expensive.
+        // FIXME(autodiff): Make autodiff also work with embed-bc instead of fat-lto.
+        if self.opts.autodiff_enabled() {
+            return config::Lto::Fat;
+        }
+
         // If our target has codegen requirements ignore the command line
         if self.target.requires_lto {
             return config::Lto::Fat;