Merge from rustc

8 files changed, 282 insertions, 112 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/archive.rs b/compiler/rustc_codegen_ssa/src/back/archive.rs
index bb76ca5d2b9..18789d00fd3 100644
--- a/compiler/rustc_codegen_ssa/src/back/archive.rs
+++ b/compiler/rustc_codegen_ssa/src/back/archive.rs
@@ -6,11 +6,12 @@ use rustc_span::symbol::Symbol;
 
 use object::read::archive::ArchiveFile;
 
-use std::fmt::Display;
 use std::fs::File;
 use std::io;
 use std::path::{Path, PathBuf};
 
+use crate::errors::ExtractBundledLibsError;
+
 pub trait ArchiveBuilderBuilder {
     fn new_archive_builder<'a>(&self, sess: &'a Session) -> Box<dyn ArchiveBuilder<'a> + 'a>;
 
@@ -28,32 +29,35 @@ pub trait ArchiveBuilderBuilder {
         is_direct_dependency: bool,
     ) -> PathBuf;
 
-    fn extract_bundled_libs(
-        &self,
-        rlib: &Path,
+    fn extract_bundled_libs<'a>(
+        &'a self,
+        rlib: &'a Path,
         outdir: &Path,
         bundled_lib_file_names: &FxHashSet<Symbol>,
-    ) -> Result<(), String> {
-        let message = |msg: &str, e: &dyn Display| format!("{} '{}': {}", msg, &rlib.display(), e);
+    ) -> Result<(), ExtractBundledLibsError<'_>> {
         let archive_map = unsafe {
-            Mmap::map(File::open(rlib).map_err(|e| message("failed to open file", &e))?)
-                .map_err(|e| message("failed to mmap file", &e))?
+            Mmap::map(
+                File::open(rlib)
+                    .map_err(|e| ExtractBundledLibsError::OpenFile { rlib, error: Box::new(e) })?,
+            )
+            .map_err(|e| ExtractBundledLibsError::MmapFile { rlib, error: Box::new(e) })?
         };
         let archive = ArchiveFile::parse(&*archive_map)
-            .map_err(|e| message("failed to parse archive", &e))?;
+            .map_err(|e| ExtractBundledLibsError::ParseArchive { rlib, error: Box::new(e) })?;
 
         for entry in archive.members() {
-            let entry = entry.map_err(|e| message("failed to read entry", &e))?;
+            let entry = entry
+                .map_err(|e| ExtractBundledLibsError::ReadEntry { rlib, error: Box::new(e) })?;
             let data = entry
                 .data(&*archive_map)
-                .map_err(|e| message("failed to get data from archive member", &e))?;
+                .map_err(|e| ExtractBundledLibsError::ArchiveMember { rlib, error: Box::new(e) })?;
             let name = std::str::from_utf8(entry.name())
-                .map_err(|e| message("failed to convert name", &e))?;
+                .map_err(|e| ExtractBundledLibsError::ConvertName { rlib, error: Box::new(e) })?;
             if !bundled_lib_file_names.contains(&Symbol::intern(name)) {
                 continue; // We need to extract only native libraries.
             }
             std::fs::write(&outdir.join(&name), data)
-                .map_err(|e| message("failed to write file", &e))?;
+                .map_err(|e| ExtractBundledLibsError::WriteFile { rlib, error: Box::new(e) })?;
         }
         Ok(())
     }
diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index 0dc0dee862c..5a1ad792924 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -919,29 +919,17 @@ fn link_natively<'a>(
                         )
                         .is_some();
 
-                        sess.note_without_error("`link.exe` returned an unexpected error");
+                        sess.emit_note(errors::LinkExeUnexpectedError);
                         if is_vs_installed && has_linker {
                             // the linker is broken
-                            sess.note_without_error(
-                                "the Visual Studio build tools may need to be repaired \
-                                using the Visual Studio installer",
-                            );
-                            sess.note_without_error(
-                                "or a necessary component may be missing from the \
-                                \"C++ build tools\" workload",
-                            );
+                            sess.emit_note(errors::RepairVSBuildTools);
+                            sess.emit_note(errors::MissingCppBuildToolComponent);
                         } else if is_vs_installed {
                             // the linker is not installed
-                            sess.note_without_error(
-                                "in the Visual Studio installer, ensure the \
-                                \"C++ build tools\" workload is selected",
-                            );
+                            sess.emit_note(errors::SelectCppBuildToolWorkload);
                         } else {
                             // visual studio is not installed
-                            sess.note_without_error(
-                                "you may need to install Visual Studio build tools with the \
-                                \"C++ build tools\" workload",
-                            );
+                            sess.emit_note(errors::VisualStudioNotInstalled);
                         }
                     }
                 }
@@ -954,35 +942,20 @@ fn link_natively<'a>(
         Err(e) => {
             let linker_not_found = e.kind() == io::ErrorKind::NotFound;
 
-            let mut linker_error = {
-                if linker_not_found {
-                    sess.struct_err(&format!("linker `{}` not found", linker_path.display()))
-                } else {
-                    sess.struct_err(&format!(
-                        "could not exec the linker `{}`",
-                        linker_path.display()
-                    ))
-                }
-            };
-
-            linker_error.note(&e.to_string());
-
-            if !linker_not_found {
-                linker_error.note(&format!("{:?}", &cmd));
+            if linker_not_found {
+                sess.emit_err(errors::LinkerNotFound { linker_path, error: e });
+            } else {
+                sess.emit_err(errors::UnableToExeLinker {
+                    linker_path,
+                    error: e,
+                    command_formatted: format!("{:?}", &cmd),
+                });
             }
 
-            linker_error.emit();
-
             if sess.target.is_like_msvc && linker_not_found {
-                sess.note_without_error(
-                    "the msvc targets depend on the msvc linker \
-                     but `link.exe` was not found",
-                );
-                sess.note_without_error(
-                    "please ensure that Visual Studio 2017 or later, or Build Tools \
-                     for Visual Studio were installed with the Visual C++ option.",
-                );
-                sess.note_without_error("VS Code is a different product, and is not sufficient.");
+                sess.emit_note(errors::MsvcMissingLinker);
+                sess.emit_note(errors::CheckInstalledVisualStudio);
+                sess.emit_note(errors::UnsufficientVSCodeProduct);
             }
             sess.abort_if_errors();
         }
@@ -1007,15 +980,13 @@ fn link_natively<'a>(
                     if !prog.status.success() {
                         let mut output = prog.stderr.clone();
                         output.extend_from_slice(&prog.stdout);
-                        sess.struct_warn(&format!(
-                            "processing debug info with `dsymutil` failed: {}",
-                            prog.status
-                        ))
-                        .note(&escape_string(&output))
-                        .emit();
+                        sess.emit_warning(errors::ProcessingDymutilFailed {
+                            status: prog.status,
+                            output: escape_string(&output),
+                        });
                     }
                 }
-                Err(e) => sess.fatal(&format!("unable to run `dsymutil`: {}", e)),
+                Err(error) => sess.emit_fatal(errors::UnableToRunDsymutil { error }),
             }
         }
 
@@ -1092,15 +1063,14 @@ fn strip_symbols_with_external_utility<'a>(
             if !prog.status.success() {
                 let mut output = prog.stderr.clone();
                 output.extend_from_slice(&prog.stdout);
-                sess.struct_warn(&format!(
-                    "stripping debug info with `{}` failed: {}",
-                    util, prog.status
-                ))
-                .note(&escape_string(&output))
-                .emit();
+                sess.emit_warning(errors::StrippingDebugInfoFailed {
+                    util,
+                    status: prog.status,
+                    output: escape_string(&output),
+                });
             }
         }
-        Err(e) => sess.fatal(&format!("unable to run `{}`: {}", util, e)),
+        Err(error) => sess.emit_fatal(errors::UnableToRun { util, error }),
     }
 }
 
@@ -1153,7 +1123,8 @@ fn link_sanitizer_runtime(sess: &Session, linker: &mut dyn Linker, name: &str) {
         if path.exists() {
             return session_tlib;
         } else {
-            let default_sysroot = filesearch::get_or_default_sysroot();
+            let default_sysroot =
+                filesearch::get_or_default_sysroot().expect("Failed finding sysroot");
             let default_tlib = filesearch::make_target_lib_path(
                 &default_sysroot,
                 sess.opts.target_triple.triple(),
@@ -1251,7 +1222,7 @@ pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
             )),
             (Some(linker), None) => {
                 let stem = linker.file_stem().and_then(|stem| stem.to_str()).unwrap_or_else(|| {
-                    sess.fatal("couldn't extract file stem from specified linker")
+                    sess.emit_fatal(errors::LinkerFileStem);
                 });
 
                 let flavor = if stem == "emcc" {
@@ -1378,13 +1349,9 @@ fn print_native_static_libs(sess: &Session, all_native_libs: &[NativeLib]) {
         })
         .collect();
     if !lib_args.is_empty() {
-        sess.note_without_error(
-            "Link against the following native artifacts when linking \
-                                 against this static library. The order and any duplication \
-                                 can be significant on some platforms.",
-        );
+        sess.emit_note(errors::StaticLibraryNativeArtifacts);
         // Prefix for greppability
-        sess.note_without_error(&format!("native-static-libs: {}", &lib_args.join(" ")));
+        sess.emit_note(errors::NativeStaticLibs { arguments: lib_args.join(" ") });
     }
 }
 
@@ -1688,14 +1655,14 @@ fn add_link_script(cmd: &mut dyn Linker, sess: &Session, tmpdir: &Path, crate_ty
     match (crate_type, &sess.target.link_script) {
         (CrateType::Cdylib | CrateType::Executable, Some(script)) => {
             if !sess.target.linker_flavor.is_gnu() {
-                sess.fatal("can only use link script when linking with GNU-like linker");
+                sess.emit_fatal(errors::LinkScriptUnavailable);
             }
 
             let file_name = ["rustc", &sess.target.llvm_target, "linkfile.ld"].join("-");
 
             let path = tmpdir.join(file_name);
-            if let Err(e) = fs::write(&path, script.as_ref()) {
-                sess.fatal(&format!("failed to write link script to {}: {}", path.display(), e));
+            if let Err(error) = fs::write(&path, script.as_ref()) {
+                sess.emit_fatal(errors::LinkScriptWriteFailure { path, error });
             }
 
             cmd.arg("--script");
@@ -1841,8 +1808,8 @@ fn add_linked_symbol_object(
 
     let path = tmpdir.join("symbols.o");
     let result = std::fs::write(&path, file.write().unwrap());
-    if let Err(e) = result {
-        sess.fatal(&format!("failed to write {}: {}", path.display(), e));
+    if let Err(error) = result {
+        sess.emit_fatal(errors::FailedToWrite { path, error });
     }
     cmd.add_object(&path);
 }
@@ -2299,14 +2266,10 @@ fn collect_natvis_visualizers(
                 visualizer_paths.push(visualizer_out_file);
             }
             Err(error) => {
-                sess.warn(
-                    format!(
-                        "Unable to write debugger visualizer file `{}`: {} ",
-                        visualizer_out_file.display(),
-                        error
-                    )
-                    .as_str(),
-                );
+                sess.emit_warning(errors::UnableToWriteDebuggerVisualizer {
+                    path: visualizer_out_file,
+                    error,
+                });
             }
         };
     }
@@ -2484,7 +2447,7 @@ fn add_upstream_rust_crates<'a>(
                         let rlib = &src.rlib.as_ref().unwrap().0;
                         archive_builder_builder
                             .extract_bundled_libs(rlib, tmpdir, &bundled_libs)
-                            .unwrap_or_else(|e| sess.fatal(e));
+                            .unwrap_or_else(|e| sess.emit_fatal(e));
                     }
 
                     let mut last = (None, NativeLibKind::Unspecified, None);
@@ -2641,7 +2604,7 @@ fn add_upstream_rust_crates<'a>(
                 || !codegen_results.crate_info.is_no_builtins.contains(&cnum);
 
             let mut archive = archive_builder_builder.new_archive_builder(sess);
-            if let Err(e) = archive.add_archive(
+            if let Err(error) = archive.add_archive(
                 cratepath,
                 Box::new(move |f| {
                     if f == METADATA_FILENAME {
@@ -2681,7 +2644,7 @@ fn add_upstream_rust_crates<'a>(
                     false
                 }),
             ) {
-                sess.fatal(&format!("failed to build archive from rlib: {}", e));
+                sess.emit_fatal(errors::RlibArchiveBuildFailure { error });
             }
             if archive.build(&dst) {
                 link_upstream(&dst);
@@ -2813,14 +2776,14 @@ fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
         ("arm", "watchos") => "watchos",
         (_, "macos") => "macosx",
         _ => {
-            sess.err(&format!("unsupported arch `{}` for os `{}`", arch, os));
+            sess.emit_err(errors::UnsupportedArch { arch, os });
             return;
         }
     };
     let sdk_root = match get_apple_sdk_root(sdk_name) {
         Ok(s) => s,
         Err(e) => {
-            sess.err(&e);
+            sess.emit_err(e);
             return;
         }
     };
@@ -2836,7 +2799,7 @@ fn add_apple_sdk(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
     }
 }
 
-fn get_apple_sdk_root(sdk_name: &str) -> Result<String, String> {
+fn get_apple_sdk_root(sdk_name: &str) -> Result<String, errors::AppleSdkRootError<'_>> {
     // Following what clang does
     // (https://github.com/llvm/llvm-project/blob/
     // 296a80102a9b72c3eda80558fb78a3ed8849b341/clang/lib/Driver/ToolChains/Darwin.cpp#L1661-L1678)
@@ -2886,7 +2849,7 @@ fn get_apple_sdk_root(sdk_name: &str) -> Result<String, String> {
 
     match res {
         Ok(output) => Ok(output.trim().to_string()),
-        Err(e) => Err(format!("failed to get {} SDK path: {}", sdk_name, e)),
+        Err(error) => Err(errors::AppleSdkRootError::SdkPath { sdk_name, error }),
     }
 }
 
@@ -2919,7 +2882,7 @@ fn add_gcc_ld_path(cmd: &mut dyn Linker, sess: &Session, flavor: LinkerFlavor) {
                 }
             }
         } else {
-            sess.fatal("option `-Z gcc-ld` is used even though linker flavor is not gcc");
+            sess.emit_fatal(errors::OptionGccOnly);
         }
     }
 }
diff --git a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
index c2ecc41601c..752f6b1ef40 100644
--- a/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
+++ b/compiler/rustc_codegen_ssa/src/back/symbol_export.rs
@@ -193,8 +193,11 @@ fn exported_symbols_provider_local<'tcx>(
     }
 
     if tcx.allocator_kind(()).is_some() {
-        for method in ALLOCATOR_METHODS {
-            let symbol_name = format!("__rust_{}", method.name);
+        for symbol_name in ALLOCATOR_METHODS
+            .iter()
+            .map(|method| format!("__rust_{}", method.name))
+            .chain(["__rust_alloc_error_handler".to_string(), OomStrategy::SYMBOL.to_string()])
+        {
             let exported_symbol = ExportedSymbol::NoDefId(SymbolName::new(tcx, &symbol_name));
 
             symbols.push((
diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index 84b89cd71a6..c1411690f82 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -22,7 +22,6 @@ use rustc_data_structures::sync::ParallelIterator;
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_hir::lang_items::LangItem;
-use rustc_hir::weak_lang_items::WEAK_ITEMS_SYMBOLS;
 use rustc_index::vec::Idx;
 use rustc_metadata::EncodedMetadata;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
@@ -639,7 +638,14 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         let llmod_id =
             cgu_name_builder.build_cgu_name(LOCAL_CRATE, &["crate"], Some("allocator")).to_string();
         let module_llvm = tcx.sess.time("write_allocator_module", || {
-            backend.codegen_allocator(tcx, &llmod_id, kind, tcx.lang_items().oom().is_some())
+            backend.codegen_allocator(
+                tcx,
+                &llmod_id,
+                kind,
+                // If allocator_kind is Some then alloc_error_handler_kind must
+                // also be Some.
+                tcx.alloc_error_handler_kind(()).unwrap(),
+            )
         });
 
         Some(ModuleCodegen { name: llmod_id, module_llvm, kind: ModuleKind::Allocator })
@@ -887,14 +893,14 @@ impl CrateInfo {
         // by the compiler, but that's ok because all this stuff is unstable anyway.
         let target = &tcx.sess.target;
         if !are_upstream_rust_objects_already_included(tcx.sess) {
-            let missing_weak_lang_items: FxHashSet<&Symbol> = info
+            let missing_weak_lang_items: FxHashSet<Symbol> = info
                 .used_crates
                 .iter()
-                .flat_map(|cnum| {
-                    tcx.missing_lang_items(*cnum)
-                        .iter()
-                        .filter(|l| lang_items::required(tcx, **l))
-                        .filter_map(|item| WEAK_ITEMS_SYMBOLS.get(item))
+                .flat_map(|&cnum| tcx.missing_lang_items(cnum))
+                .filter(|l| l.is_weak())
+                .filter_map(|&l| {
+                    let name = l.link_name()?;
+                    lang_items::required(tcx, l).then_some(name)
                 })
                 .collect();
             let prefix = if target.is_like_windows && target.arch == "x86" { "_" } else { "" };
diff --git a/compiler/rustc_codegen_ssa/src/errors.rs b/compiler/rustc_codegen_ssa/src/errors.rs
index ebb531f1c43..36c94462b0b 100644
--- a/compiler/rustc_codegen_ssa/src/errors.rs
+++ b/compiler/rustc_codegen_ssa/src/errors.rs
@@ -354,3 +354,170 @@ impl IntoDiagnostic<'_> for LinkingFailed<'_> {
         diag
     }
 }
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_link_exe_unexpected_error)]
+pub struct LinkExeUnexpectedError;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_repair_vs_build_tools)]
+pub struct RepairVSBuildTools;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_missing_cpp_build_tool_component)]
+pub struct MissingCppBuildToolComponent;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_select_cpp_build_tool_workload)]
+pub struct SelectCppBuildToolWorkload;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_visual_studio_not_installed)]
+pub struct VisualStudioNotInstalled;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_linker_not_found)]
+#[note]
+pub struct LinkerNotFound {
+    pub linker_path: PathBuf,
+    pub error: Error,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_unable_to_exe_linker)]
+#[note]
+#[note(command_note)]
+pub struct UnableToExeLinker {
+    pub linker_path: PathBuf,
+    pub error: Error,
+    pub command_formatted: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_msvc_missing_linker)]
+pub struct MsvcMissingLinker;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_check_installed_visual_studio)]
+pub struct CheckInstalledVisualStudio;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_unsufficient_vs_code_product)]
+pub struct UnsufficientVSCodeProduct;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_processing_dymutil_failed)]
+#[note]
+pub struct ProcessingDymutilFailed {
+    pub status: ExitStatus,
+    pub output: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_unable_to_run_dsymutil)]
+#[note]
+pub struct UnableToRunDsymutil {
+    pub error: Error,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_stripping_debu_info_failed)]
+#[note]
+pub struct StrippingDebugInfoFailed<'a> {
+    pub util: &'a str,
+    pub status: ExitStatus,
+    pub output: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_unable_to_run)]
+pub struct UnableToRun<'a> {
+    pub util: &'a str,
+    pub error: Error,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_linker_file_stem)]
+pub struct LinkerFileStem;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_static_library_native_artifacts)]
+pub struct StaticLibraryNativeArtifacts;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_native_static_libs)]
+pub struct NativeStaticLibs {
+    pub arguments: String,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_link_script_unavailable)]
+pub struct LinkScriptUnavailable;
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_link_script_write_failure)]
+pub struct LinkScriptWriteFailure {
+    pub path: PathBuf,
+    pub error: Error,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_failed_to_write)]
+pub struct FailedToWrite {
+    pub path: PathBuf,
+    pub error: Error,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_unable_to_write_debugger_visualizer)]
+pub struct UnableToWriteDebuggerVisualizer {
+    pub path: PathBuf,
+    pub error: Error,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_rlib_archive_build_failure)]
+pub struct RlibArchiveBuildFailure {
+    pub error: Error,
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_option_gcc_only)]
+pub struct OptionGccOnly;
+
+#[derive(Diagnostic)]
+pub enum ExtractBundledLibsError<'a> {
+    #[diag(codegen_ssa_extract_bundled_libs_open_file)]
+    OpenFile { rlib: &'a Path, error: Box<dyn std::error::Error> },
+
+    #[diag(codegen_ssa_extract_bundled_libs_mmap_file)]
+    MmapFile { rlib: &'a Path, error: Box<dyn std::error::Error> },
+
+    #[diag(codegen_ssa_extract_bundled_libs_parse_archive)]
+    ParseArchive { rlib: &'a Path, error: Box<dyn std::error::Error> },
+
+    #[diag(codegen_ssa_extract_bundled_libs_read_entry)]
+    ReadEntry { rlib: &'a Path, error: Box<dyn std::error::Error> },
+
+    #[diag(codegen_ssa_extract_bundled_libs_archive_member)]
+    ArchiveMember { rlib: &'a Path, error: Box<dyn std::error::Error> },
+
+    #[diag(codegen_ssa_extract_bundled_libs_convert_name)]
+    ConvertName { rlib: &'a Path, error: Box<dyn std::error::Error> },
+
+    #[diag(codegen_ssa_extract_bundled_libs_write_file)]
+    WriteFile { rlib: &'a Path, error: Box<dyn std::error::Error> },
+}
+
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_unsupported_arch)]
+pub struct UnsupportedArch<'a> {
+    pub arch: &'a str,
+    pub os: &'a str,
+}
+
+#[derive(Diagnostic)]
+pub enum AppleSdkRootError<'a> {
+    #[diag(codegen_ssa_apple_sdk_error_sdk_path)]
+    SdkPath { sdk_name: &'a str, error: Error },
+}
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 29b7c9b0a88..0802067cde6 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -17,6 +17,7 @@ use rustc_middle::mir::{self, AssertKind, SwitchTargets};
 use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
 use rustc_middle::ty::print::{with_no_trimmed_paths, with_no_visible_paths};
 use rustc_middle::ty::{self, Instance, Ty, TypeVisitable};
+use rustc_session::config::OptLevel;
 use rustc_span::source_map::Span;
 use rustc_span::{sym, Symbol};
 use rustc_symbol_mangling::typeid::typeid_for_fnabi;
@@ -286,12 +287,13 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         assert_eq!(discr.layout.ty, switch_ty);
         let mut target_iter = targets.iter();
         if target_iter.len() == 1 {
-            // If there are two targets (one conditional, one fallback), emit br instead of switch
+            // If there are two targets (one conditional, one fallback), emit `br` instead of
+            // `switch`.
             let (test_value, target) = target_iter.next().unwrap();
             let lltrue = helper.llbb_with_cleanup(self, target);
             let llfalse = helper.llbb_with_cleanup(self, targets.otherwise());
             if switch_ty == bx.tcx().types.bool {
-                // Don't generate trivial icmps when switching on bool
+                // Don't generate trivial icmps when switching on bool.
                 match test_value {
                     0 => bx.cond_br(discr.immediate(), llfalse, lltrue),
                     1 => bx.cond_br(discr.immediate(), lltrue, llfalse),
@@ -303,6 +305,30 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 let cmp = bx.icmp(IntPredicate::IntEQ, discr.immediate(), llval);
                 bx.cond_br(cmp, lltrue, llfalse);
             }
+        } else if self.cx.sess().opts.optimize == OptLevel::No
+            && target_iter.len() == 2
+            && self.mir[targets.otherwise()].is_empty_unreachable()
+        {
+            // In unoptimized builds, if there are two normal targets and the `otherwise` target is
+            // an unreachable BB, emit `br` instead of `switch`. This leaves behind the unreachable
+            // BB, which will usually (but not always) be dead code.
+            //
+            // Why only in unoptimized builds?
+            // - In unoptimized builds LLVM uses FastISel which does not support switches, so it
+            //   must fall back to the to the slower SelectionDAG isel. Therefore, using `br` gives
+            //   significant compile time speedups for unoptimized builds.
+            // - In optimized builds the above doesn't hold, and using `br` sometimes results in
+            //   worse generated code because LLVM can no longer tell that the value being switched
+            //   on can only have two values, e.g. 0 and 1.
+            //
+            let (test_value1, target1) = target_iter.next().unwrap();
+            let (_test_value2, target2) = target_iter.next().unwrap();
+            let ll1 = helper.llbb_with_cleanup(self, target1);
+            let ll2 = helper.llbb_with_cleanup(self, target2);
+            let switch_llty = bx.immediate_backend_type(bx.layout_of(switch_ty));
+            let llval = bx.const_uint_big(switch_llty, test_value1);
+            let cmp = bx.icmp(IntPredicate::IntEQ, discr.immediate(), llval);
+            bx.cond_br(cmp, ll1, ll2);
         } else {
             bx.switch(
                 discr.immediate(),
diff --git a/compiler/rustc_codegen_ssa/src/target_features.rs b/compiler/rustc_codegen_ssa/src/target_features.rs
index 83407ee8f9d..a4368303de5 100644
--- a/compiler/rustc_codegen_ssa/src/target_features.rs
+++ b/compiler/rustc_codegen_ssa/src/target_features.rs
@@ -267,6 +267,7 @@ const WASM_ALLOWED_FEATURES: &[(&str, Option<Symbol>)] = &[
     // tidy-alphabetical-start
     ("atomics", Some(sym::wasm_target_feature)),
     ("bulk-memory", Some(sym::wasm_target_feature)),
+    ("multivalue", Some(sym::wasm_target_feature)),
     ("mutable-globals", Some(sym::wasm_target_feature)),
     ("nontrapping-fptoint", Some(sym::wasm_target_feature)),
     ("reference-types", Some(sym::wasm_target_feature)),
diff --git a/compiler/rustc_codegen_ssa/src/traits/backend.rs b/compiler/rustc_codegen_ssa/src/traits/backend.rs
index 87e347c61e2..5c35070ea66 100644
--- a/compiler/rustc_codegen_ssa/src/traits/backend.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/backend.rs
@@ -119,7 +119,7 @@ pub trait ExtraBackendMethods: CodegenBackend + WriteBackendMethods + Sized + Se
         tcx: TyCtxt<'tcx>,
         module_name: &str,
         kind: AllocatorKind,
-        has_alloc_error_handler: bool,
+        alloc_error_handler_kind: AllocatorKind,
     ) -> Self::Module;
     /// This generates the codegen unit and returns it along with
     /// a `u64` giving an estimate of the unit's processing cost.