Add a feature flag for the JIT

Cargo.toml

@@ -12,6 +12,7 @@ crate-type = ["dylib"]
 cranelift-codegen = { git = "https://github.com/bytecodealliance/wasmtime/", branch = "main", features = ["unwind"] }
 cranelift-frontend = { git = "https://github.com/bytecodealliance/wasmtime/", branch = "main" }
 cranelift-module = { git = "https://github.com/bytecodealliance/wasmtime/", branch = "main" }
+cranelift-simplejit = { git = "https://github.com/bytecodealliance/wasmtime/", branch = "main", optional = true }
 cranelift-object = { git = "https://github.com/bytecodealliance/wasmtime/", branch = "main" }
 target-lexicon = "0.10.0"
 
@@ -19,6 +20,7 @@ ar = "0.8.0"
 byteorder = "1.2.7"
 indexmap = "1.0.2"
 cfg-if = "0.1.10"
+libloading = { version = "0.6.0", optional = true }
 
 [dependencies.object]
 version = "0.20.0"
@@ -41,9 +43,9 @@ features = ["write"] # We don't need read support
 #[patch.crates-io]
 #gimli = { path = "../" }
 
-[target.'cfg(not(target_arch = "wasm32"))'.dependencies]
+[features]
-cranelift-simplejit = { git = "https://github.com/bytecodealliance/wasmtime/", branch = "main" }
+default = ["jit"]
-libloading = "0.6.0"
+jit = ["cranelift-simplejit", "libloading"]
 
 [profile.dev]
 # By compiling dependencies with optimizations, performing tests gets much faster.

src/atomic_shim.rs

@@ -5,6 +5,7 @@
 
 use crate::prelude::*;
 
+#[cfg(feature = "jit")]
 #[no_mangle]
 pub static mut __cg_clif_global_atomic_mutex: libc::pthread_mutex_t = libc::PTHREAD_MUTEX_INITIALIZER;
 

src/debuginfo/emit.rs

@@ -1,5 +1,3 @@
-use std::convert::TryInto;
-
 use rustc_data_structures::fx::FxHashMap;
 
 use gimli::write::{Address, AttributeValue, EndianVec, Result, Sections, Writer};
@@ -70,10 +68,13 @@ impl WriterRelocate {
         }
     }
 
+    #[cfg(feature = "jit")]
     pub(super) fn relocate_for_jit(
         mut self,
         jit_module: &mut cranelift_module::Module<cranelift_simplejit::SimpleJITBackend>,
     ) -> Vec<u8> {
+        use std::convert::TryInto;
+
         for reloc in self.relocs.drain(..) {
             match reloc.name {
                 super::DebugRelocName::Section(_) => unreachable!(),

src/debuginfo/unwind.rs

@@ -69,6 +69,7 @@ impl<'tcx> UnwindContext<'tcx> {
         }
     }
 
+    #[cfg(feature = "jit")]
     pub(crate) unsafe fn register_jit(
         self,
         jit_module: &mut Module<cranelift_simplejit::SimpleJITBackend>,

src/driver/mod.rs

@@ -6,7 +6,7 @@ use rustc_middle::mir::mono::{Linkage as RLinkage, MonoItem, Visibility};
 use crate::prelude::*;
 
 mod aot;
-#[cfg(not(target_arch = "wasm32"))]
+#[cfg(feature = "jit")]
 mod jit;
 
 pub(crate) fn codegen_crate(
@@ -19,11 +19,11 @@ pub(crate) fn codegen_crate(
     if std::env::var("CG_CLIF_JIT").is_ok()
         && tcx.sess.crate_types().contains(&rustc_session::config::CrateType::Executable)
     {
-        #[cfg(not(target_arch = "wasm32"))]
+        #[cfg(feature = "jit")]
         let _: ! = jit::run_jit(tcx);
 
-        #[cfg(target_arch = "wasm32")]
+        #[cfg(not(feature = "jit"))]
-        panic!("jit not supported on wasm");
+        tcx.sess.fatal("jit support was disabled when compiling rustc_codegen_cranelift");
     }
 
     aot::run_aot(tcx, metadata, need_metadata_module)

src/lib.rs

@@ -4,6 +4,7 @@
 #![warn(unused_lifetimes)]
 
 extern crate flate2;
+#[cfg(feature = "jit")]
 extern crate libc;
 extern crate rustc_middle;
 extern crate rustc_codegen_ssa;