Put unwinding support behind a cargo feature

Author: bjorn3

Cargo.toml

@@ -46,6 +46,7 @@ smallvec = "1.8.1"
 unstable-features = ["jit", "inline_asm_sym"]
 jit = ["cranelift-jit", "libloading"]
 inline_asm_sym = []
+unwinding = [] # Not yet included in unstable-features for performance reasons
 
 [package.metadata.rust-analyzer]
 rustc_private = true

build_system/abi_cafe.rs

@@ -19,6 +19,7 @@ pub(crate) fn run(
     cg_clif_dylib: &CodegenBackend,
     rustup_toolchain_name: Option<&str>,
     bootstrap_host_compiler: &Compiler,
+    panic_unwind_support: bool,
 ) {
     std::fs::create_dir_all(&dirs.download_dir).unwrap();
     ABI_CAFE_REPO.fetch(dirs);
@@ -32,6 +33,7 @@ pub(crate) fn run(
         bootstrap_host_compiler,
         rustup_toolchain_name,
         bootstrap_host_compiler.triple.clone(),
+        panic_unwind_support,
     );
 
     eprintln!("Running abi-cafe");

build_system/build_backend.rs

@@ -12,6 +12,7 @@ pub(crate) fn build_backend(
     dirs: &Dirs,
     bootstrap_host_compiler: &Compiler,
     use_unstable_features: bool,
+    panic_unwind_support: bool,
 ) -> PathBuf {
     let _group = LogGroup::guard("Build backend");
 
@@ -31,6 +32,10 @@ pub(crate) fn build_backend(
         cmd.arg("--features").arg("unstable-features");
     }
 
+    if panic_unwind_support {
+        cmd.arg("--features").arg("unwinding");
+    }
+
     cmd.arg("--release");
 
     eprintln!("[BUILD] rustc_codegen_cranelift");

build_system/build_sysroot.rs

@@ -17,6 +17,7 @@ pub(crate) fn build_sysroot(
     bootstrap_host_compiler: &Compiler,
     rustup_toolchain_name: Option<&str>,
     target_triple: String,
+    panic_unwind_support: bool,
 ) -> Compiler {
     let _guard = LogGroup::guard("Build sysroot");
 
@@ -52,6 +53,9 @@ pub(crate) fn build_sysroot(
             .arg("-o")
             .arg(&wrapper_path)
             .arg("-Cstrip=debuginfo");
+        if panic_unwind_support {
+            build_cargo_wrapper_cmd.arg("--cfg").arg("support_panic_unwind");
+        }
         if let Some(rustup_toolchain_name) = &rustup_toolchain_name {
             build_cargo_wrapper_cmd
                 .env("TOOLCHAIN_NAME", rustup_toolchain_name)
@@ -77,6 +81,7 @@ pub(crate) fn build_sysroot(
         bootstrap_host_compiler.clone(),
         &cg_clif_dylib_path,
         sysroot_kind,
+        panic_unwind_support,
     );
     host.install_into_sysroot(dist_dir);
 
@@ -91,6 +96,7 @@ pub(crate) fn build_sysroot(
             },
             &cg_clif_dylib_path,
             sysroot_kind,
+            panic_unwind_support,
         )
         .install_into_sysroot(dist_dir);
     }
@@ -141,12 +147,15 @@ fn build_sysroot_for_triple(
     compiler: Compiler,
     cg_clif_dylib_path: &CodegenBackend,
     sysroot_kind: SysrootKind,
+    panic_unwind_support: bool,
 ) -> SysrootTarget {
     match sysroot_kind {
         SysrootKind::None => build_rtstartup(dirs, &compiler)
             .unwrap_or(SysrootTarget { triple: compiler.triple, libs: vec![] }),
         SysrootKind::Llvm => build_llvm_sysroot_for_triple(compiler),
-        SysrootKind::Clif => build_clif_sysroot_for_triple(dirs, compiler, cg_clif_dylib_path),
+        SysrootKind::Clif => {
+            build_clif_sysroot_for_triple(dirs, compiler, cg_clif_dylib_path, panic_unwind_support)
+        }
     }
 }
 
@@ -188,6 +197,7 @@ fn build_clif_sysroot_for_triple(
     dirs: &Dirs,
     mut compiler: Compiler,
     cg_clif_dylib_path: &CodegenBackend,
+    panic_unwind_support: bool,
 ) -> SysrootTarget {
     let mut target_libs = SysrootTarget { triple: compiler.triple.clone(), libs: vec![] };
 
@@ -206,7 +216,10 @@ fn build_clif_sysroot_for_triple(
     }
 
     // Build sysroot
-    let mut rustflags = vec!["-Zforce-unstable-if-unmarked".to_owned(), "-Cpanic=abort".to_owned()];
+    let mut rustflags = vec!["-Zforce-unstable-if-unmarked".to_owned()];
+    if !panic_unwind_support {
+        rustflags.push("-Cpanic=abort".to_owned());
+    }
     match cg_clif_dylib_path {
         CodegenBackend::Local(path) => {
             rustflags.push(format!("-Zcodegen-backend={}", path.to_str().unwrap()));

build_system/main.rs

@@ -83,6 +83,7 @@ fn main() {
     let mut download_dir = None;
     let mut sysroot_kind = SysrootKind::Clif;
     let mut use_unstable_features = true;
+    let mut panic_unwind_support = false;
     let mut frozen = false;
     let mut skip_tests = vec![];
     let mut use_backend = None;
@@ -108,6 +109,7 @@ fn main() {
                 }
             }
             "--no-unstable-features" => use_unstable_features = false,
+            "--panic-unwind-support" => panic_unwind_support = true,
             "--frozen" => frozen = true,
             "--skip-test" => {
                 // FIXME check that all passed in tests actually exist
@@ -201,6 +203,7 @@ fn main() {
             &dirs,
             &bootstrap_host_compiler,
             use_unstable_features,
+            panic_unwind_support,
         ))
     };
     match command {
@@ -212,6 +215,7 @@ fn main() {
                 &dirs,
                 sysroot_kind,
                 use_unstable_features,
+                panic_unwind_support,
                 &skip_tests.iter().map(|test| &**test).collect::<Vec<_>>(),
                 &cg_clif_dylib,
                 &bootstrap_host_compiler,
@@ -230,6 +234,7 @@ fn main() {
                 &cg_clif_dylib,
                 rustup_toolchain_name.as_deref(),
                 &bootstrap_host_compiler,
+                panic_unwind_support,
             );
         }
         Command::Build => {
@@ -240,6 +245,7 @@ fn main() {
                 &bootstrap_host_compiler,
                 rustup_toolchain_name.as_deref(),
                 target_triple,
+                panic_unwind_support,
             );
         }
         Command::Bench => {
@@ -250,6 +256,7 @@ fn main() {
                 &bootstrap_host_compiler,
                 rustup_toolchain_name.as_deref(),
                 target_triple,
+                panic_unwind_support,
             );
             bench::benchmark(&dirs, &compiler);
         }

build_system/tests.rs

@@ -233,6 +233,7 @@ pub(crate) fn run_tests(
     dirs: &Dirs,
     sysroot_kind: SysrootKind,
     use_unstable_features: bool,
+    panic_unwind_support: bool,
     skip_tests: &[&str],
     cg_clif_dylib: &CodegenBackend,
     bootstrap_host_compiler: &Compiler,
@@ -251,12 +252,14 @@ pub(crate) fn run_tests(
             bootstrap_host_compiler,
             rustup_toolchain_name,
             target_triple.clone(),
+            panic_unwind_support,
         );
 
         let runner = TestRunner::new(
             dirs.clone(),
             target_compiler,
             use_unstable_features,
+            panic_unwind_support,
             skip_tests,
             bootstrap_host_compiler.triple == target_triple,
             stdlib_source.clone(),
@@ -283,12 +286,14 @@ pub(crate) fn run_tests(
             bootstrap_host_compiler,
             rustup_toolchain_name,
             target_triple.clone(),
+            panic_unwind_support,
         );
 
         let mut runner = TestRunner::new(
             dirs.clone(),
             target_compiler,
             use_unstable_features,
+            panic_unwind_support,
             skip_tests,
             bootstrap_host_compiler.triple == target_triple,
             stdlib_source,
@@ -314,6 +319,7 @@ pub(crate) fn run_tests(
 struct TestRunner<'a> {
     is_native: bool,
     jit_supported: bool,
+    panic_unwind_support: bool,
     skip_tests: &'a [&'a str],
     dirs: Dirs,
     target_compiler: Compiler,
@@ -325,6 +331,7 @@ impl<'a> TestRunner<'a> {
         dirs: Dirs,
         mut target_compiler: Compiler,
         use_unstable_features: bool,
+        panic_unwind_support: bool,
         skip_tests: &'a [&'a str],
         is_native: bool,
         stdlib_source: PathBuf,
@@ -335,7 +342,15 @@ impl<'a> TestRunner<'a> {
         let jit_supported =
             use_unstable_features && is_native && !target_compiler.triple.contains("windows");
 
-        Self { is_native, jit_supported, skip_tests, dirs, target_compiler, stdlib_source }
+        Self {
+            is_native,
+            jit_supported,
+            panic_unwind_support,
+            skip_tests,
+            dirs,
+            target_compiler,
+            stdlib_source,
+        }
     }
 
     fn run_testsuite(&self, tests: &[TestCase]) {
@@ -404,7 +419,9 @@ impl<'a> TestRunner<'a> {
         cmd.arg("-Cdebuginfo=2");
         cmd.arg("--target");
         cmd.arg(&self.target_compiler.triple);
-        cmd.arg("-Cpanic=abort");
+        if !self.panic_unwind_support {
+            cmd.arg("-Cpanic=abort");
+        }
         cmd.arg("--check-cfg=cfg(jit)");
         cmd.args(args);
         cmd

build_system/usage.txt

@@ -25,6 +25,10 @@ OPTIONS:
             Some features are not yet ready for production usage. This option will disable these
             features. This includes the JIT mode and inline assembly support.
 
+    --panic-unwind-support
+            Enable support for unwinding when -Cpanic=unwind is used. This currently regresses build
+            performance.
+
     --frozen
             Require Cargo.lock and cache are up to date
 

scripts/cargo-clif.rs

@@ -12,7 +12,11 @@ fn main() {
         sysroot = sysroot.parent().unwrap();
     }
 
-    let mut rustflags = vec!["-Cpanic=abort".to_owned(), "-Zpanic-abort-tests".to_owned()];
+    let mut rustflags = vec![];
+    if !cfg!(support_panic_unwind) {
+        rustflags.push("-Cpanic=abort".to_owned());
+        rustflags.push("-Zpanic-abort-tests".to_owned());
+    }
     if let Some(name) = option_env!("BUILTIN_BACKEND") {
         rustflags.push(format!("-Zcodegen-backend={name}"));
     } else {

scripts/rustc-clif.rs

@@ -17,8 +17,10 @@ fn main() {
 
     let passed_args = std::env::args_os().skip(1).collect::<Vec<_>>();
     let mut args = vec![];
-    args.push(OsString::from("-Cpanic=abort"));
-    args.push(OsString::from("-Zpanic-abort-tests"));
+    if !cfg!(support_panic_unwind) {
+        args.push(OsString::from("-Cpanic=abort"));
+        args.push(OsString::from("-Zpanic-abort-tests"));
+    }
     if let Some(name) = option_env!("BUILTIN_BACKEND") {
         args.push(OsString::from(format!("-Zcodegen-backend={name}")))
     } else {

scripts/rustdoc-clif.rs

@@ -17,8 +17,10 @@ fn main() {
 
     let passed_args = std::env::args_os().skip(1).collect::<Vec<_>>();
     let mut args = vec![];
-    args.push(OsString::from("-Cpanic=abort"));
-    args.push(OsString::from("-Zpanic-abort-tests"));
+    if !cfg!(support_panic_unwind) {
+        args.push(OsString::from("-Cpanic=abort"));
+        args.push(OsString::from("-Zpanic-abort-tests"));
+    }
     if let Some(name) = option_env!("BUILTIN_BACKEND") {
         args.push(OsString::from(format!("-Zcodegen-backend={name}")))
     } else {

src/abi/mod.rs

@@ -844,7 +844,7 @@ pub(crate) fn codegen_call_with_unwind_action(
     fx: &mut FunctionCx<'_, '_, '_>,
     span: Span,
     func_ref: CallTarget,
-    unwind: UnwindAction,
+    mut unwind: UnwindAction,
     call_args: &[Value],
     target_block: Option<Block>,
 ) -> SmallVec<[Value; 2]> {
@@ -856,6 +856,11 @@ pub(crate) fn codegen_call_with_unwind_action(
     if target_block.is_some() {
         assert!(fx.bcx.func.dfg.signatures[sig_ref].returns.is_empty());
     }
+
+    if cfg!(not(feature = "unwinding")) {
+        unwind = UnwindAction::Unreachable;
+    }
+
     match unwind {
         UnwindAction::Continue | UnwindAction::Unreachable => {
             let call_inst = match func_ref {

src/base.rs

@@ -300,6 +300,10 @@ fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
         }
 
         if bb_data.is_cleanup {
+            if cfg!(not(feature = "unwinding")) {
+                continue;
+            }
+
             fx.bcx.set_cold_block(block);
         }
 
@@ -534,13 +538,15 @@ fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
                 codegen_unwind_terminate(fx, source_info.span, *reason);
             }
             TerminatorKind::UnwindResume => {
-                let exception_ptr = fx.bcx.use_var(fx.exception_slot);
-                fx.lib_call(
-                    "_Unwind_Resume",
-                    vec![AbiParam::new(fx.pointer_type)],
-                    vec![],
-                    &[exception_ptr],
-                );
+                if cfg!(feature = "unwinding") {
+                    let exception_ptr = fx.bcx.use_var(fx.exception_slot);
+                    fx.lib_call(
+                        "_Unwind_Resume",
+                        vec![AbiParam::new(fx.pointer_type)],
+                        vec![],
+                        &[exception_ptr],
+                    );
+                }
                 fx.bcx.ins().trap(TrapCode::user(1 /* unreachable */).unwrap());
             }
             TerminatorKind::Unreachable => {