Auto merge of #83864 - Dylan-DPC:rollup-78an86n, r=Dylan-DPC

Rollup of 7 pull requests

Successful merges:

 - #80525 (wasm64 support)
 - #83019 (core: disable `ptr::swap_nonoverlapping_one`'s block optimization on SPIR-V.)
 - #83717 (rustdoc: Separate filter-empty-string out into its own function)
 - #83807 (Tests: Remove redundant `ignore-tidy-linelength` annotations)
 - #83815 (ptr::addr_of documentation improvements)
 - #83820 (Remove attribute `#[link_args]`)
 - #83841 (Allow clobbering unsupported registers in asm!)

Failed merges:

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

29 files changed, 209 insertions, 136 deletions

diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index 32fb8d1c8f4..d5a9d7ee6e3 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/compiler/rustc_ast_lowering/src/expr.rs
@@ -1499,46 +1499,64 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 // previous iteration.
                 required_features.clear();
 
-                // Validate register classes against currently enabled target
-                // features. We check that at least one type is available for
-                // the current target.
                 let reg_class = reg.reg_class();
                 if reg_class == asm::InlineAsmRegClass::Err {
                     continue;
                 }
-                for &(_, feature) in reg_class.supported_types(asm_arch.unwrap()) {
-                    if let Some(feature) = feature {
-                        if self.sess.target_features.contains(&Symbol::intern(feature)) {
+
+                // We ignore target feature requirements for clobbers: if the
+                // feature is disabled then the compiler doesn't care what we
+                // do with the registers.
+                //
+                // Note that this is only possible for explicit register
+                // operands, which cannot be used in the asm string.
+                let is_clobber = matches!(
+                    op,
+                    hir::InlineAsmOperand::Out {
+                        reg: asm::InlineAsmRegOrRegClass::Reg(_),
+                        late: _,
+                        expr: None
+                    }
+                );
+
+                if !is_clobber {
+                    // Validate register classes against currently enabled target
+                    // features. We check that at least one type is available for
+                    // the current target.
+                    for &(_, feature) in reg_class.supported_types(asm_arch.unwrap()) {
+                        if let Some(feature) = feature {
+                            if self.sess.target_features.contains(&Symbol::intern(feature)) {
+                                required_features.clear();
+                                break;
+                            } else {
+                                required_features.push(feature);
+                            }
+                        } else {
                             required_features.clear();
                             break;
-                        } else {
-                            required_features.push(feature);
                         }
-                    } else {
-                        required_features.clear();
-                        break;
                     }
-                }
-                // We are sorting primitive strs here and can use unstable sort here
-                required_features.sort_unstable();
-                required_features.dedup();
-                match &required_features[..] {
-                    [] => {}
-                    [feature] => {
-                        let msg = format!(
-                            "register class `{}` requires the `{}` target feature",
-                            reg_class.name(),
-                            feature
-                        );
-                        sess.struct_span_err(op_sp, &msg).emit();
-                    }
-                    features => {
-                        let msg = format!(
-                            "register class `{}` requires at least one target feature: {}",
-                            reg_class.name(),
-                            features.join(", ")
-                        );
-                        sess.struct_span_err(op_sp, &msg).emit();
+                    // We are sorting primitive strs here and can use unstable sort here
+                    required_features.sort_unstable();
+                    required_features.dedup();
+                    match &required_features[..] {
+                        [] => {}
+                        [feature] => {
+                            let msg = format!(
+                                "register class `{}` requires the `{}` target feature",
+                                reg_class.name(),
+                                feature
+                            );
+                            sess.struct_span_err(op_sp, &msg).emit();
+                        }
+                        features => {
+                            let msg = format!(
+                                "register class `{}` requires at least one target feature: {}",
+                                reg_class.name(),
+                                features.join(", ")
+                            );
+                            sess.struct_span_err(op_sp, &msg).emit();
+                        }
                     }
                 }
 
diff --git a/compiler/rustc_codegen_llvm/src/asm.rs b/compiler/rustc_codegen_llvm/src/asm.rs
index e7d359c4f14..84b091d8d4d 100644
--- a/compiler/rustc_codegen_llvm/src/asm.rs
+++ b/compiler/rustc_codegen_llvm/src/asm.rs
@@ -14,7 +14,7 @@ use rustc_data_structures::fx::FxHashMap;
 use rustc_hir as hir;
 use rustc_middle::ty::layout::TyAndLayout;
 use rustc_middle::{bug, span_bug};
-use rustc_span::{Pos, Span};
+use rustc_span::{Pos, Span, Symbol};
 use rustc_target::abi::*;
 use rustc_target::asm::*;
 
@@ -125,15 +125,39 @@ impl AsmBuilderMethods<'tcx> for Builder<'a, 'll, 'tcx> {
 
         // Collect the types of output operands
         let mut constraints = vec![];
+        let mut clobbers = vec![];
         let mut output_types = vec![];
         let mut op_idx = FxHashMap::default();
         for (idx, op) in operands.iter().enumerate() {
             match *op {
                 InlineAsmOperandRef::Out { reg, late, place } => {
+                    let is_target_supported = |reg_class: InlineAsmRegClass| {
+                        for &(_, feature) in reg_class.supported_types(asm_arch) {
+                            if let Some(feature) = feature {
+                                if self.tcx.sess.target_features.contains(&Symbol::intern(feature))
+                                {
+                                    return true;
+                                }
+                            } else {
+                                // Register class is unconditionally supported
+                                return true;
+                            }
+                        }
+                        false
+                    };
+
                     let mut layout = None;
                     let ty = if let Some(ref place) = place {
                         layout = Some(&place.layout);
                         llvm_fixup_output_type(self.cx, reg.reg_class(), &place.layout)
+                    } else if !is_target_supported(reg.reg_class()) {
+                        // We turn discarded outputs into clobber constraints
+                        // if the target feature needed by the register class is
+                        // disabled. This is necessary otherwise LLVM will try
+                        // to actually allocate a register for the dummy output.
+                        assert!(matches!(reg, InlineAsmRegOrRegClass::Reg(_)));
+                        clobbers.push(format!("~{}", reg_to_llvm(reg, None)));
+                        continue;
                     } else {
                         // If the output is discarded, we don't really care what
                         // type is used. We're just using this to tell LLVM to
@@ -244,6 +268,7 @@ impl AsmBuilderMethods<'tcx> for Builder<'a, 'll, 'tcx> {
             }
         }
 
+        constraints.append(&mut clobbers);
         if !options.contains(InlineAsmOptions::PRESERVES_FLAGS) {
             match asm_arch {
                 InlineAsmArch::AArch64 | InlineAsmArch::Arm => {
diff --git a/compiler/rustc_codegen_llvm/src/attributes.rs b/compiler/rustc_codegen_llvm/src/attributes.rs
index 594d42c9366..6e1d4eba842 100644
--- a/compiler/rustc_codegen_llvm/src/attributes.rs
+++ b/compiler/rustc_codegen_llvm/src/attributes.rs
@@ -317,7 +317,7 @@ pub fn from_fn_attrs(cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value, instance: ty::
     // Note that currently the `wasm-import-module` doesn't do anything, but
     // eventually LLVM 7 should read this and ferry the appropriate import
     // module to the output file.
-    if cx.tcx.sess.target.arch == "wasm32" {
+    if cx.tcx.sess.target.is_like_wasm {
         if let Some(module) = wasm_import_module(cx.tcx, instance.def_id()) {
             llvm::AddFunctionAttrStringValue(
                 llfn,
diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs
index b3551177323..82f3ee07c93 100644
--- a/compiler/rustc_codegen_llvm/src/back/write.rs
+++ b/compiler/rustc_codegen_llvm/src/back/write.rs
@@ -170,10 +170,7 @@ pub fn target_machine_factory(
     // On the wasm target once the `atomics` feature is enabled that means that
     // we're no longer single-threaded, or otherwise we don't want LLVM to
     // lower atomic operations to single-threaded operations.
-    if singlethread
-        && sess.target.llvm_target.contains("wasm32")
-        && sess.target_features.contains(&sym::atomics)
-    {
+    if singlethread && sess.target.is_like_wasm && sess.target_features.contains(&sym::atomics) {
         singlethread = false;
     }
 
diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
index d90e93f116c..e6fa852155b 100644
--- a/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
+++ b/compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs
@@ -1083,9 +1083,9 @@ pub fn compile_unit_metadata(
             );
         }
 
-        // Insert `llvm.ident` metadata on the wasm32 targets since that will
+        // Insert `llvm.ident` metadata on the wasm targets since that will
         // get hooked up to the "producer" sections `processed-by` information.
-        if tcx.sess.opts.target_triple.triple().starts_with("wasm32") {
+        if tcx.sess.target.is_like_wasm {
             let name_metadata = llvm::LLVMMDStringInContext(
                 debug_context.llcontext,
                 rustc_producer.as_ptr().cast(),
diff --git a/compiler/rustc_codegen_ssa/src/back/link.rs b/compiler/rustc_codegen_ssa/src/back/link.rs
index 217b8f43229..ea75943d6f3 100644
--- a/compiler/rustc_codegen_ssa/src/back/link.rs
+++ b/compiler/rustc_codegen_ssa/src/back/link.rs
@@ -1411,15 +1411,10 @@ fn add_link_script(cmd: &mut dyn Linker, sess: &Session, tmpdir: &Path, crate_ty
     }
 }
 
-/// Add arbitrary "user defined" args defined from command line and by `#[link_args]` attributes.
+/// Add arbitrary "user defined" args defined from command line.
 /// FIXME: Determine where exactly these args need to be inserted.
-fn add_user_defined_link_args(
-    cmd: &mut dyn Linker,
-    sess: &Session,
-    codegen_results: &CodegenResults,
-) {
+fn add_user_defined_link_args(cmd: &mut dyn Linker, sess: &Session) {
     cmd.args(&sess.opts.cg.link_args);
-    cmd.args(&*codegen_results.crate_info.link_args);
 }
 
 /// Add arbitrary "late link" args defined by the target spec.
@@ -1761,7 +1756,7 @@ fn linker_with_args<'a, B: ArchiveBuilder<'a>>(
     add_rpath_args(cmd, sess, codegen_results, out_filename);
 
     // OBJECT-FILES-MAYBE, CUSTOMIZATION-POINT
-    add_user_defined_link_args(cmd, sess, codegen_results);
+    add_user_defined_link_args(cmd, sess);
 
     // NO-OPT-OUT, OBJECT-FILES-NO, AUDIT-ORDER
     cmd.finalize();
diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index e19274e579b..77d8ab49ff2 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -186,7 +186,7 @@ impl<'a> GccLinker<'a> {
         // * On OSX they have their own linker, not binutils'
         // * For WebAssembly the only functional linker is LLD, which doesn't
         //   support hint flags
-        !self.sess.target.is_like_osx && self.sess.target.arch != "wasm32"
+        !self.sess.target.is_like_osx && !self.sess.target.is_like_wasm
     }
 
     // Some platforms take hints about whether a library is static or dynamic.
diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index 08e31c3b37f..318eed76acf 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -754,7 +754,6 @@ impl CrateInfo {
             is_no_builtins: Default::default(),
             native_libraries: Default::default(),
             used_libraries: tcx.native_libraries(LOCAL_CRATE).iter().map(Into::into).collect(),
-            link_args: tcx.link_args(LOCAL_CRATE),
             crate_name: Default::default(),
             used_crates_dynamic: cstore::used_crates(tcx, LinkagePreference::RequireDynamic),
             used_crates_static: cstore::used_crates(tcx, LinkagePreference::RequireStatic),
diff --git a/compiler/rustc_codegen_ssa/src/lib.rs b/compiler/rustc_codegen_ssa/src/lib.rs
index 56b4ef79383..f0f45b067b3 100644
--- a/compiler/rustc_codegen_ssa/src/lib.rs
+++ b/compiler/rustc_codegen_ssa/src/lib.rs
@@ -139,7 +139,6 @@ pub struct CrateInfo {
     pub native_libraries: FxHashMap<CrateNum, Vec<NativeLib>>,
     pub crate_name: FxHashMap<CrateNum, String>,
     pub used_libraries: Vec<NativeLib>,
-    pub link_args: Lrc<Vec<String>>,
     pub used_crate_source: FxHashMap<CrateNum, Lrc<CrateSource>>,
     pub used_crates_static: Vec<(CrateNum, LibSource)>,
     pub used_crates_dynamic: Vec<(CrateNum, LibSource)>,
diff --git a/compiler/rustc_codegen_ssa/src/target_features.rs b/compiler/rustc_codegen_ssa/src/target_features.rs
index a69e6d2b86d..4e987908b4e 100644
--- a/compiler/rustc_codegen_ssa/src/target_features.rs
+++ b/compiler/rustc_codegen_ssa/src/target_features.rs
@@ -161,7 +161,7 @@ pub fn supported_target_features(sess: &Session) -> &'static [(&'static str, Opt
         "mips" | "mips64" => MIPS_ALLOWED_FEATURES,
         "powerpc" | "powerpc64" => POWERPC_ALLOWED_FEATURES,
         "riscv32" | "riscv64" => RISCV_ALLOWED_FEATURES,
-        "wasm32" => WASM_ALLOWED_FEATURES,
+        "wasm32" | "wasm64" => WASM_ALLOWED_FEATURES,
         _ => &[],
     }
 }
diff --git a/compiler/rustc_feature/src/active.rs b/compiler/rustc_feature/src/active.rs
index 040260f5cf5..abbeb9554e3 100644
--- a/compiler/rustc_feature/src/active.rs
+++ b/compiler/rustc_feature/src/active.rs
@@ -258,9 +258,6 @@ declare_features! (
     // feature-group-start: actual feature gates
     // -------------------------------------------------------------------------
 
-    /// Allows using the `#[link_args]` attribute.
-    (active, link_args, "1.0.0", Some(29596), None),
-
     /// Allows defining identifiers beyond ASCII.
     (active, non_ascii_idents, "1.0.0", Some(55467), None),
 
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index 072062dd615..7df9b3f0a79 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -280,11 +280,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // Linking:
     gated!(naked, AssumedUsed, template!(Word), naked_functions, experimental!(naked)),
     gated!(
-        link_args, Normal, template!(NameValueStr: "args"),
-        "the `link_args` attribute is experimental and not portable across platforms, \
-        it is recommended to use `#[link(name = \"foo\")] instead",
-    ),
-    gated!(
         link_ordinal, AssumedUsed, template!(List: "ordinal"), raw_dylib,
         experimental!(link_ordinal)
     ),
diff --git a/compiler/rustc_feature/src/removed.rs b/compiler/rustc_feature/src/removed.rs
index 8ba67a00f8d..e1491576616 100644
--- a/compiler/rustc_feature/src/removed.rs
+++ b/compiler/rustc_feature/src/removed.rs
@@ -128,6 +128,10 @@ declare_features! (
     /// Allows comparing raw pointers during const eval.
     (removed, const_compare_raw_pointers, "1.46.0", Some(53020), None,
      Some("cannot be allowed in const eval in any meaningful way")),
+    /// Allows using the `#[link_args]` attribute.
+    (removed, link_args, "1.53.0", Some(29596), None,
+     Some("removed in favor of using `-C link-arg=ARG` on command line, \
+           which is available from cargo build scripts with `cargo:rustc-link-arg` now")),
 
     // -------------------------------------------------------------------------
     // feature-group-end: removed features
diff --git a/compiler/rustc_metadata/src/lib.rs b/compiler/rustc_metadata/src/lib.rs
index fe93f4230e9..c4d9e3f77f0 100644
--- a/compiler/rustc_metadata/src/lib.rs
+++ b/compiler/rustc_metadata/src/lib.rs
@@ -26,7 +26,6 @@ pub use rmeta::{provide, provide_extern};
 
 mod dependency_format;
 mod foreign_modules;
-mod link_args;
 mod native_libs;
 mod rmeta;
 
diff --git a/compiler/rustc_metadata/src/link_args.rs b/compiler/rustc_metadata/src/link_args.rs
deleted file mode 100644
index 9e1ac33368c..00000000000
--- a/compiler/rustc_metadata/src/link_args.rs
+++ /dev/null
@@ -1,57 +0,0 @@
-use rustc_hir as hir;
-use rustc_hir::itemlikevisit::ItemLikeVisitor;
-use rustc_middle::ty::TyCtxt;
-use rustc_span::symbol::{sym, Symbol};
-use rustc_target::spec::abi::Abi;
-
-crate fn collect(tcx: TyCtxt<'_>) -> Vec<String> {
-    let mut collector = Collector { tcx, args: Vec::new() };
-    tcx.hir().krate().visit_all_item_likes(&mut collector);
-
-    for attr in tcx.hir().attrs(hir::CRATE_HIR_ID).iter() {
-        if attr.has_name(sym::link_args) {
-            if let Some(linkarg) = attr.value_str() {
-                collector.add_link_args(linkarg);
-            }
-        }
-    }
-
-    collector.args
-}
-
-struct Collector<'tcx> {
-    tcx: TyCtxt<'tcx>,
-    args: Vec<String>,
-}
-
-impl<'tcx> ItemLikeVisitor<'tcx> for Collector<'tcx> {
-    fn visit_item(&mut self, it: &'tcx hir::Item<'tcx>) {
-        let abi = match it.kind {
-            hir::ItemKind::ForeignMod { abi, .. } => abi,
-            _ => return,
-        };
-        if abi == Abi::Rust || abi == Abi::RustIntrinsic || abi == Abi::PlatformIntrinsic {
-            return;
-        }
-
-        // First, add all of the custom #[link_args] attributes
-        let sess = &self.tcx.sess;
-        for m in
-            self.tcx.hir().attrs(it.hir_id()).iter().filter(|a| sess.check_name(a, sym::link_args))
-        {
-            if let Some(linkarg) = m.value_str() {
-                self.add_link_args(linkarg);
-            }
-        }
-    }
-
-    fn visit_trait_item(&mut self, _it: &'tcx hir::TraitItem<'tcx>) {}
-    fn visit_impl_item(&mut self, _it: &'tcx hir::ImplItem<'tcx>) {}
-    fn visit_foreign_item(&mut self, _it: &'tcx hir::ForeignItem<'tcx>) {}
-}
-
-impl<'tcx> Collector<'tcx> {
-    fn add_link_args(&mut self, args: Symbol) {
-        self.args.extend(args.as_str().split(' ').filter(|s| !s.is_empty()).map(|s| s.to_string()))
-    }
-}
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index e10041a2971..bebee9dac3b 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -1,6 +1,5 @@
 use crate::creader::{CStore, LoadedMacro};
 use crate::foreign_modules;
-use crate::link_args;
 use crate::native_libs;
 use crate::rmeta::{self, encoder};
 
@@ -295,10 +294,6 @@ pub fn provide(providers: &mut Providers) {
                 foreign_modules::collect(tcx).into_iter().map(|m| (m.def_id, m)).collect();
             Lrc::new(modules)
         },
-        link_args: |tcx, cnum| {
-            assert_eq!(cnum, LOCAL_CRATE);
-            Lrc::new(link_args::collect(tcx))
-        },
 
         // Returns a map from a sufficiently visible external item (i.e., an
         // external item that is visible from at least one local module) to a
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index bf39b1da8f0..bac69e282a5 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1253,11 +1253,6 @@ rustc_queries! {
         desc { |tcx| "native_library_kind({})", tcx.def_path_str(def_id) }
     }
 
-    query link_args(_: CrateNum) -> Lrc<Vec<String>> {
-        eval_always
-        desc { "looking up link arguments for a crate" }
-    }
-
     /// Does lifetime resolution, but does not descend into trait items. This
     /// should only be used for resolving lifetimes of on trait definitions,
     /// and is used to avoid cycles. Importantly, `resolve_lifetimes` still visits
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index c7d561f760b..b67feb47173 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -822,6 +822,9 @@ pub fn default_configuration(sess: &Session) -> CrateConfig {
         }
     }
     ret.insert((sym::target_arch, Some(Symbol::intern(arch))));
+    if sess.target.is_like_wasm {
+        ret.insert((sym::wasm, None));
+    }
     ret.insert((sym::target_endian, Some(Symbol::intern(end.as_str()))));
     ret.insert((sym::target_pointer_width, Some(Symbol::intern(&wordsz))));
     ret.insert((sym::target_env, Some(Symbol::intern(env))));
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index c5f929ab183..e4810fe7059 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1294,6 +1294,7 @@ symbols! {
         vreg,
         vreg_low16,
         warn,
+        wasm,
         wasm_import_module,
         wasm_target_feature,
         while_let,
diff --git a/compiler/rustc_symbol_mangling/src/lib.rs b/compiler/rustc_symbol_mangling/src/lib.rs
index 3dd7ce93deb..c050bbc9b9d 100644
--- a/compiler/rustc_symbol_mangling/src/lib.rs
+++ b/compiler/rustc_symbol_mangling/src/lib.rs
@@ -198,7 +198,7 @@ fn compute_symbol_name(
     //
     // [1]: https://bugs.llvm.org/show_bug.cgi?id=44316
     if is_foreign
-        && (tcx.sess.target.arch != "wasm32"
+        && (!tcx.sess.target.is_like_wasm
             || !tcx.wasm_import_module_map(def_id.krate).contains_key(&def_id))
     {
         if let Some(name) = attrs.link_name {
diff --git a/compiler/rustc_target/src/abi/call/mod.rs b/compiler/rustc_target/src/abi/call/mod.rs
index 2c3f7762759..395235399ea 100644
--- a/compiler/rustc_target/src/abi/call/mod.rs
+++ b/compiler/rustc_target/src/abi/call/mod.rs
@@ -20,6 +20,7 @@ mod sparc;
 mod sparc64;
 mod wasm32;
 mod wasm32_bindgen_compat;
+mod wasm64;
 mod x86;
 mod x86_64;
 mod x86_win64;
@@ -652,6 +653,7 @@ impl<'a, Ty> FnAbi<'a, Ty> {
                 _ => wasm32_bindgen_compat::compute_abi_info(self),
             },
             "asmjs" => wasm32::compute_abi_info(cx, self),
+            "wasm64" => wasm64::compute_abi_info(cx, self),
             a => return Err(format!("unrecognized arch \"{}\" in target specification", a)),
         }
 
diff --git a/compiler/rustc_target/src/abi/call/wasm64.rs b/compiler/rustc_target/src/abi/call/wasm64.rs
new file mode 100644
index 00000000000..46d670d1689
--- /dev/null
+++ b/compiler/rustc_target/src/abi/call/wasm64.rs
@@ -0,0 +1,58 @@
+use crate::abi::call::{ArgAbi, FnAbi, Uniform};
+use crate::abi::{HasDataLayout, LayoutOf, TyAndLayout, TyAndLayoutMethods};
+
+fn unwrap_trivial_aggregate<'a, Ty, C>(cx: &C, val: &mut ArgAbi<'a, Ty>) -> bool
+where
+    Ty: TyAndLayoutMethods<'a, C> + Copy,
+    C: LayoutOf<Ty = Ty, TyAndLayout = TyAndLayout<'a, Ty>> + HasDataLayout,
+{
+    if val.layout.is_aggregate() {
+        if let Some(unit) = val.layout.homogeneous_aggregate(cx).ok().and_then(|ha| ha.unit()) {
+            let size = val.layout.size;
+            if unit.size == size {
+                val.cast_to(Uniform { unit, total: size });
+                return true;
+            }
+        }
+    }
+    false
+}
+
+fn classify_ret<'a, Ty, C>(cx: &C, ret: &mut ArgAbi<'a, Ty>)
+where
+    Ty: TyAndLayoutMethods<'a, C> + Copy,
+    C: LayoutOf<Ty = Ty, TyAndLayout = TyAndLayout<'a, Ty>> + HasDataLayout,
+{
+    ret.extend_integer_width_to(64);
+    if ret.layout.is_aggregate() && !unwrap_trivial_aggregate(cx, ret) {
+        ret.make_indirect();
+    }
+}
+
+fn classify_arg<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'a, Ty>)
+where
+    Ty: TyAndLayoutMethods<'a, C> + Copy,
+    C: LayoutOf<Ty = Ty, TyAndLayout = TyAndLayout<'a, Ty>> + HasDataLayout,
+{
+    arg.extend_integer_width_to(64);
+    if arg.layout.is_aggregate() && !unwrap_trivial_aggregate(cx, arg) {
+        arg.make_indirect_byval();
+    }
+}
+
+pub fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
+where
+    Ty: TyAndLayoutMethods<'a, C> + Copy,
+    C: LayoutOf<Ty = Ty, TyAndLayout = TyAndLayout<'a, Ty>> + HasDataLayout,
+{
+    if !fn_abi.ret.is_ignore() {
+        classify_ret(cx, &mut fn_abi.ret);
+    }
+
+    for arg in &mut fn_abi.args {
+        if arg.is_ignore() {
+            continue;
+        }
+        classify_arg(cx, arg);
+    }
+}
diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
index 89052ef390b..801cdd3ebe9 100644
--- a/compiler/rustc_target/src/spec/mod.rs
+++ b/compiler/rustc_target/src/spec/mod.rs
@@ -79,7 +79,7 @@ mod solaris_base;
 mod thumb_base;
 mod uefi_msvc_base;
 mod vxworks_base;
-mod wasm32_base;
+mod wasm_base;
 mod windows_gnu_base;
 mod windows_msvc_base;
 mod windows_uwp_gnu_base;
@@ -842,6 +842,7 @@ supported_targets! {
     ("wasm32-unknown-emscripten", wasm32_unknown_emscripten),
     ("wasm32-unknown-unknown", wasm32_unknown_unknown),
     ("wasm32-wasi", wasm32_wasi),
+    ("wasm64-unknown-unknown", wasm64_unknown_unknown),
 
     ("thumbv6m-none-eabi", thumbv6m_none_eabi),
     ("thumbv7m-none-eabi", thumbv7m_none_eabi),
@@ -1076,6 +1077,8 @@ pub struct TargetOptions {
     pub is_like_emscripten: bool,
     /// Whether the target toolchain is like Fuchsia's.
     pub is_like_fuchsia: bool,
+    /// Whether a target toolchain is like WASM.
+    pub is_like_wasm: bool,
     /// Version of DWARF to use if not using the default.
     /// Useful because some platforms (osx, bsd) only want up to DWARF2.
     pub dwarf_version: Option<u32>,
@@ -1295,6 +1298,7 @@ impl Default for TargetOptions {
             is_like_emscripten: false,
             is_like_msvc: false,
             is_like_fuchsia: false,
+            is_like_wasm: false,
             dwarf_version: None,
             linker_is_gnu: false,
             allows_weak_linkage: true,
@@ -1789,6 +1793,7 @@ impl Target {
         key!(is_like_msvc, bool);
         key!(is_like_emscripten, bool);
         key!(is_like_fuchsia, bool);
+        key!(is_like_wasm, bool);
         key!(dwarf_version, Option<u32>);
         key!(linker_is_gnu, bool);
         key!(allows_weak_linkage, bool);
@@ -2027,6 +2032,7 @@ impl ToJson for Target {
         target_option_val!(is_like_msvc);
         target_option_val!(is_like_emscripten);
         target_option_val!(is_like_fuchsia);
+        target_option_val!(is_like_wasm);
         target_option_val!(dwarf_version);
         target_option_val!(linker_is_gnu);
         target_option_val!(allows_weak_linkage);
diff --git a/compiler/rustc_target/src/spec/tests/tests_impl.rs b/compiler/rustc_target/src/spec/tests/tests_impl.rs
index 9ec8467e0ac..f4de8bc0a58 100644
--- a/compiler/rustc_target/src/spec/tests/tests_impl.rs
+++ b/compiler/rustc_target/src/spec/tests/tests_impl.rs
@@ -50,6 +50,7 @@ impl Target {
     // and you certainly want "unknown" for the OS name.
     fn can_use_os_unknown(&self) -> bool {
         self.llvm_target == "wasm32-unknown-unknown"
+            || self.llvm_target == "wasm64-unknown-unknown"
             || (self.env == "sgx" && self.vendor == "fortanix")
     }
 }
diff --git a/compiler/rustc_target/src/spec/wasm32_unknown_emscripten.rs b/compiler/rustc_target/src/spec/wasm32_unknown_emscripten.rs
index 58d7633fa62..e028dbaa325 100644
--- a/compiler/rustc_target/src/spec/wasm32_unknown_emscripten.rs
+++ b/compiler/rustc_target/src/spec/wasm32_unknown_emscripten.rs
@@ -1,8 +1,8 @@
-use super::wasm32_base;
+use super::wasm_base;
 use super::{LinkArgs, LinkerFlavor, PanicStrategy, Target, TargetOptions};
 
 pub fn target() -> Target {
-    let mut options = wasm32_base::options();
+    let mut options = wasm_base::options();
 
     let clang_args = options.pre_link_args.entry(LinkerFlavor::Gcc).or_default();
 
diff --git a/compiler/rustc_target/src/spec/wasm32_unknown_unknown.rs b/compiler/rustc_target/src/spec/wasm32_unknown_unknown.rs
index 73a5e16c82b..0a88ee42629 100644
--- a/compiler/rustc_target/src/spec/wasm32_unknown_unknown.rs
+++ b/compiler/rustc_target/src/spec/wasm32_unknown_unknown.rs
@@ -10,11 +10,11 @@
 //! This target is more or less managed by the Rust and WebAssembly Working
 //! Group nowadays at <https://github.com/rustwasm>.
 
-use super::wasm32_base;
+use super::wasm_base;
 use super::{LinkerFlavor, LldFlavor, Target};
 
 pub fn target() -> Target {
-    let mut options = wasm32_base::options();
+    let mut options = wasm_base::options();
     options.os = "unknown".to_string();
     options.linker_flavor = LinkerFlavor::Lld(LldFlavor::Wasm);
     let clang_args = options.pre_link_args.entry(LinkerFlavor::Gcc).or_default();
diff --git a/compiler/rustc_target/src/spec/wasm32_wasi.rs b/compiler/rustc_target/src/spec/wasm32_wasi.rs
index 3f44acdc36b..a6b12d2ee8f 100644
--- a/compiler/rustc_target/src/spec/wasm32_wasi.rs
+++ b/compiler/rustc_target/src/spec/wasm32_wasi.rs
@@ -72,11 +72,11 @@
 //! best we can with this target. Don't start relying on too much here unless
 //! you know what you're getting in to!
 
-use super::wasm32_base;
+use super::wasm_base;
 use super::{crt_objects, LinkerFlavor, LldFlavor, Target};
 
 pub fn target() -> Target {
-    let mut options = wasm32_base::options();
+    let mut options = wasm_base::options();
 
     options.os = "wasi".to_string();
     options.linker_flavor = LinkerFlavor::Lld(LldFlavor::Wasm);
diff --git a/compiler/rustc_target/src/spec/wasm64_unknown_unknown.rs b/compiler/rustc_target/src/spec/wasm64_unknown_unknown.rs
new file mode 100644
index 00000000000..8bfb229d77f
--- /dev/null
+++ b/compiler/rustc_target/src/spec/wasm64_unknown_unknown.rs
@@ -0,0 +1,39 @@
+//! A "bare wasm" target representing a WebAssembly output that makes zero
+//! assumptions about its environment.
+//!
+//! The `wasm64-unknown-unknown` target is intended to encapsulate use cases
+//! that do not rely on any imported functionality. The binaries generated are
+//! entirely self-contained by default when using the standard library. Although
+//! the standard library is available, most of it returns an error immediately
+//! (e.g. trying to create a TCP stream or something like that).
+
+use super::wasm_base;
+use super::{LinkerFlavor, LldFlavor, Target};
+
+pub fn target() -> Target {
+    let mut options = wasm_base::options();
+    options.os = "unknown".to_string();
+    options.linker_flavor = LinkerFlavor::Lld(LldFlavor::Wasm);
+    let clang_args = options.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap();
+
+    // Make sure clang uses LLD as its linker and is configured appropriately
+    // otherwise
+    clang_args.push("--target=wasm64-unknown-unknown".to_string());
+
+    // For now this target just never has an entry symbol no matter the output
+    // type, so unconditionally pass this.
+    clang_args.push("-Wl,--no-entry".to_string());
+    options
+        .pre_link_args
+        .get_mut(&LinkerFlavor::Lld(LldFlavor::Wasm))
+        .unwrap()
+        .push("--no-entry".to_string());
+
+    Target {
+        llvm_target: "wasm64-unknown-unknown".to_string(),
+        pointer_width: 64,
+        data_layout: "e-m:e-p:64:64-i64:64-n32:64-S128".to_string(),
+        arch: "wasm64".to_string(),
+        options,
+    }
+}
diff --git a/compiler/rustc_target/src/spec/wasm32_base.rs b/compiler/rustc_target/src/spec/wasm_base.rs
index bfef3d37228..c93ad24225a 100644
--- a/compiler/rustc_target/src/spec/wasm32_base.rs
+++ b/compiler/rustc_target/src/spec/wasm_base.rs
@@ -60,6 +60,8 @@ pub fn options() -> TargetOptions {
     pre_link_args.insert(LinkerFlavor::Gcc, clang_args);
 
     TargetOptions {
+        is_like_wasm: true,
+
         // we allow dynamic linking, but only cdylibs. Basically we allow a
         // final library artifact that exports some symbols (a wasm module) but
         // we don't allow intermediate `dylib` crate types