Only use coresimd when codegen_backend is LLVM

Author: bjorn3

src/bootstrap/bin/rustc.rs

@@ -107,6 +107,13 @@ fn main() {
              env::join_paths(&dylib_path).unwrap());
     let mut maybe_crate = None;
 
+    // Don't use metadata only backend for snapshot compiler, because it may be broken
+    if env::var("RUSTC_SHOULD_USE_METADATA_ONLY_BACKEND").is_ok() && stage != "0" {
+        //cmd.arg("-Zcodegen-backend=metadata_only");
+    } else {
+        cmd.arg("--cfg").arg("codegen_backend=\"llvm\"");
+    }
+
     // Print backtrace in case of ICE
     if env::var("RUSTC_BACKTRACE_ON_ICE").is_ok() && env::var("RUST_BACKTRACE").is_err() {
         cmd.env("RUST_BACKTRACE", "1");

src/bootstrap/builder.rs

@@ -747,6 +747,10 @@ impl<'a> Builder<'a> {
             stage = compiler.stage;
         }
 
+        if self.config.rust_codegen_backends.is_empty() {
+            cargo.env("RUSTC_SHOULD_USE_METADATA_ONLY_BACKEND", "1");
+        }
+
         let mut extra_args = env::var(&format!("RUSTFLAGS_STAGE_{}", stage)).unwrap_or_default();
         if stage != 0 {
             let s = env::var("RUSTFLAGS_STAGE_NOT_0").unwrap_or_default();

src/libcore/lib.rs

@@ -241,12 +241,13 @@ macro_rules! vector_impl { ($([$f:ident, $($args:tt)*]),*) => { $($f!($($args)*)
 #[path = "../stdsimd/coresimd/mod.rs"]
 #[allow(missing_docs, missing_debug_implementations, dead_code, unused_imports)]
 #[unstable(feature = "stdsimd", issue = "48556")]
-#[cfg(not(stage0))] // allow changes to how stdsimd works in stage0
+// allow changes to how stdsimd works in stage0 and don't use whithout LLVM
+#[cfg(all(not(stage0), codegen_backend="llvm"))]
 mod coresimd;
 
 #[unstable(feature = "stdsimd", issue = "48556")]
-#[cfg(not(stage0))]
+#[cfg(all(not(stage0), codegen_backend="llvm"))]
 pub use coresimd::simd;
 #[stable(feature = "simd_arch", since = "1.27.0")]
-#[cfg(not(stage0))]
+#[cfg(all(not(stage0), codegen_backend="llvm"))]
 pub use coresimd::arch;

src/librustc/session/config.rs

@@ -1418,6 +1418,18 @@ pub fn default_configuration(sess: &Session) -> ast::CrateConfig {
     if sess.opts.crate_types.contains(&CrateTypeProcMacro) {
         ret.insert((Symbol::intern("proc_macro"), None));
     }
+    /*if nightly_options::is_nightly_build() {
+        let backend_name = sess.opts
+            .debugging_opts
+            .codegen_backend
+            .as_ref()
+            .map(|s| s as &str)
+            .unwrap_or("llvm");
+        ret.insert((
+            Symbol::intern("codegen_backend"),
+            Some(Symbol::intern(backend_name)),
+        ));
+    }*/
     return ret;
 }
 

src/libstd/lib.rs

@@ -523,22 +523,22 @@ pub mod rt;
 #[path = "../stdsimd/stdsimd/mod.rs"]
 #[allow(missing_debug_implementations, missing_docs, dead_code)]
 #[unstable(feature = "stdsimd", issue = "48556")]
-#[cfg(all(not(stage0), not(test)))]
+#[cfg(all(not(stage0), not(test), codegen_backend="llvm"))]
 mod stdsimd;
 
 // A "fake" module needed by the `stdsimd` module to compile, not actually
 // exported though.
-#[cfg(not(stage0))]
+#[cfg(all(not(stage0), codegen_backend="llvm"))]
 mod coresimd {
     pub use core::arch;
     pub use core::simd;
 }
 
 #[unstable(feature = "stdsimd", issue = "48556")]
-#[cfg(all(not(stage0), not(test)))]
+#[cfg(all(not(stage0), not(test), codegen_backend="llvm"))]
 pub use stdsimd::simd;
 #[stable(feature = "simd_arch", since = "1.27.0")]
-#[cfg(all(not(stage0), not(test)))]
+#[cfg(all(not(stage0), not(test), codegen_backend="llvm"))]
 pub use stdsimd::arch;
 
 // Include a number of private modules that exist solely to provide