rustc: Add a new wasm ABI

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -196,6 +196,14 @@ impl<'a> PostExpansionVisitor<'a> {
                     "thiscall-unwind ABI is experimental and subject to change"
                 );
             }
+            "wasm" => {
+                gate_feature_post!(
+                    &self,
+                    wasm_abi,
+                    span,
+                    "wasm ABI is experimental and subject to change"
+                );
+            }
             abi => self
                 .sess
                 .parse_sess

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -13,6 +13,7 @@ use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::config::OptLevel;
 use rustc_session::Session;
+use rustc_target::spec::abi::Abi;
 use rustc_target::spec::{SanitizerSet, StackProbeType};
 
 use crate::attributes;
@@ -293,7 +294,7 @@ pub fn from_fn_attrs(cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value, instance: ty::
     // The target doesn't care; the subtarget reads our attribute.
     apply_tune_cpu_attr(cx, llfn);
 
-    let function_features = codegen_fn_attrs
+    let mut function_features = codegen_fn_attrs
         .target_features
         .iter()
         .map(|f| {
@@ -305,23 +306,10 @@ pub fn from_fn_attrs(cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value, instance: ty::
             InstructionSetAttr::ArmT32 => "+thumb-mode".to_string(),
         }))
         .collect::<Vec<String>>();
-    if !function_features.is_empty() {
-        let mut global_features = llvm_util::llvm_global_features(cx.tcx.sess);
-        global_features.extend(function_features.into_iter());
-        let features = global_features.join(",");
-        let val = CString::new(features).unwrap();
-        llvm::AddFunctionAttrStringValue(
-            llfn,
-            llvm::AttributePlace::Function,
-            cstr!("target-features"),
-            &val,
-        );
-    }
 
-    // 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.is_like_wasm {
+        // If this function is an import from the environment but the wasm
+        // import has a specific module/name, apply them here.
         if let Some(module) = wasm_import_module(cx.tcx, instance.def_id()) {
             llvm::AddFunctionAttrStringValue(
                 llfn,
@@ -340,6 +328,30 @@ pub fn from_fn_attrs(cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value, instance: ty::
                 &name,
             );
         }
+
+        // The `"wasm"` abi on wasm targets automatically enables the
+        // `+multivalue` feature because the purpose of the wasm abi is to match
+        // the WebAssembly specification, which has this feature. This won't be
+        // needed when LLVM enables this `multivalue` feature by default.
+        if !cx.tcx.is_closure(instance.def_id()) {
+            let abi = cx.tcx.fn_sig(instance.def_id()).abi();
+            if abi == Abi::Wasm {
+                function_features.push("+multivalue".to_string());
+            }
+        }
+    }
+
+    if !function_features.is_empty() {
+        let mut global_features = llvm_util::llvm_global_features(cx.tcx.sess);
+        global_features.extend(function_features.into_iter());
+        let features = global_features.join(",");
+        let val = CString::new(features).unwrap();
+        llvm::AddFunctionAttrStringValue(
+            llfn,
+            llvm::AttributePlace::Function,
+            cstr!("target-features"),
+            &val,
+        );
     }
 }
 

compiler/rustc_feature/src/active.rs

@@ -645,6 +645,9 @@ declare_features! (
     /// Allows using `#[repr(align(...))]` on function items
     (active, fn_align, "1.53.0", Some(82232), None),
 
+    /// Allows `extern "wasm" fn`
+    (active, wasm_abi, "1.53.0", Some(83788), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

compiler/rustc_middle/src/ty/layout.rs

@@ -2630,6 +2630,7 @@ fn fn_can_unwind(
                 | AvrInterrupt
                 | AvrNonBlockingInterrupt
                 | CCmseNonSecureCall
+                | Wasm
                 | RustIntrinsic
                 | PlatformIntrinsic
                 | Unadjusted => false,
@@ -2712,6 +2713,7 @@ where
             AmdGpuKernel => Conv::AmdGpuKernel,
             AvrInterrupt => Conv::AvrInterrupt,
             AvrNonBlockingInterrupt => Conv::AvrNonBlockingInterrupt,
+            Wasm => Conv::C,
 
             // These API constants ought to be more specific...
             Cdecl => Conv::C,

compiler/rustc_mir_build/src/build/mod.rs

@@ -609,6 +609,7 @@ fn should_abort_on_panic(tcx: TyCtxt<'_>, fn_def_id: LocalDefId, abi: Abi) -> bo
                 | AvrInterrupt
                 | AvrNonBlockingInterrupt
                 | CCmseNonSecureCall
+                | Wasm
                 | RustIntrinsic
                 | PlatformIntrinsic
                 | Unadjusted => true,

compiler/rustc_span/src/symbol.rs

@@ -1295,6 +1295,7 @@ symbols! {
         vreg,
         vreg_low16,
         warn,
+        wasm_abi,
         wasm_import_module,
         wasm_target_feature,
         while_let,

compiler/rustc_target/src/abi/call/mod.rs

@@ -18,9 +18,7 @@ mod riscv;
 mod s390x;
 mod sparc;
 mod sparc64;
-mod wasm32;
-mod wasm32_bindgen_compat;
-mod wasm64;
+mod wasm;
 mod x86;
 mod x86_64;
 mod x86_win64;
@@ -648,12 +646,14 @@ impl<'a, Ty> FnAbi<'a, Ty> {
             "nvptx64" => nvptx64::compute_abi_info(self),
             "hexagon" => hexagon::compute_abi_info(self),
             "riscv32" | "riscv64" => riscv::compute_abi_info(cx, self),
-            "wasm32" => match cx.target_spec().os.as_str() {
-                "emscripten" | "wasi" => wasm32::compute_abi_info(cx, self),
-                _ => wasm32_bindgen_compat::compute_abi_info(self),
-            },
-            "asmjs" => wasm32::compute_abi_info(cx, self),
-            "wasm64" => wasm64::compute_abi_info(cx, self),
+            "wasm32" | "wasm64" => {
+                if cx.target_spec().adjust_abi(abi) == spec::abi::Abi::Wasm {
+                    wasm::compute_wasm_abi_info(self)
+                } else {
+                    wasm::compute_c_abi_info(cx, self)
+                }
+            }
+            "asmjs" => wasm::compute_c_abi_info(cx, self),
             a => return Err(format!("unrecognized arch \"{}\" in target specification", a)),
         }
 

compiler/rustc_target/src/abi/call/wasm32.rs → compiler/rustc_target/src/abi/call/wasm.rs

@@ -40,7 +40,8 @@ where
     }
 }
 
-pub fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)
+/// The purpose of this ABI is to match the C ABI (aka clang) exactly.
+pub fn compute_c_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,
@@ -56,3 +57,27 @@ where
         classify_arg(cx, arg);
     }
 }
+
+/// The purpose of this ABI is for matching the WebAssembly standard. This
+/// intentionally diverges from the C ABI and is specifically crafted to take
+/// advantage of LLVM's support of multiple returns in WebAssembly.
+pub fn compute_wasm_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
+    if !fn_abi.ret.is_ignore() {
+        classify_ret(&mut fn_abi.ret);
+    }
+
+    for arg in &mut fn_abi.args {
+        if arg.is_ignore() {
+            continue;
+        }
+        classify_arg(arg);
+    }
+
+    fn classify_ret<Ty>(ret: &mut ArgAbi<'_, Ty>) {
+        ret.extend_integer_width_to(32);
+    }
+
+    fn classify_arg<Ty>(arg: &mut ArgAbi<'_, Ty>) {
+        arg.extend_integer_width_to(32);
+    }
+}

compiler/rustc_target/src/spec/abi.rs

@@ -34,6 +34,7 @@ pub enum Abi {
     AvrInterrupt,
     AvrNonBlockingInterrupt,
     CCmseNonSecureCall,
+    Wasm,
 
     // Multiplatform / generic ABIs
     System { unwind: bool },
@@ -83,6 +84,7 @@ const AbiDatas: &[AbiData] = &[
         generic: false,
     },
     AbiData { abi: Abi::CCmseNonSecureCall, name: "C-cmse-nonsecure-call", generic: false },
+    AbiData { abi: Abi::Wasm, name: "wasm", generic: false },
     // Cross-platform ABIs
     AbiData { abi: Abi::System { unwind: false }, name: "system", generic: true },
     AbiData { abi: Abi::System { unwind: true }, name: "system-unwind", generic: true },
@@ -131,13 +133,14 @@ impl Abi {
             AvrInterrupt => 18,
             AvrNonBlockingInterrupt => 19,
             CCmseNonSecureCall => 20,
+            Wasm => 21,
             // Cross-platform ABIs
-            System { unwind: false } => 21,
-            System { unwind: true } => 22,
-            RustIntrinsic => 23,
-            RustCall => 24,
-            PlatformIntrinsic => 25,
-            Unadjusted => 26,
+            System { unwind: false } => 22,
+            System { unwind: true } => 23,
+            RustIntrinsic => 24,
+            RustCall => 25,
+            PlatformIntrinsic => 26,
+            Unadjusted => 27,
         };
         debug_assert!(
             AbiDatas

compiler/rustc_target/src/spec/mod.rs

@@ -1254,6 +1254,9 @@ pub struct TargetOptions {
     /// enabled can generated on this target, but the necessary supporting libraries are not
     /// distributed with the target, the sanitizer should still appear in this list for the target.
     pub supported_sanitizers: SanitizerSet,
+
+    /// If present it's a default value to use for adjusting the C ABI.
+    pub default_adjusted_cabi: Option<Abi>,
 }
 
 impl Default for TargetOptions {
@@ -1357,6 +1360,7 @@ impl Default for TargetOptions {
             has_thumb_interworking: false,
             split_debuginfo: SplitDebuginfo::Off,
             supported_sanitizers: SanitizerSet::empty(),
+            default_adjusted_cabi: None,
         }
     }
 }
@@ -1408,6 +1412,9 @@ impl Target {
                     Abi::C { unwind: false }
                 }
             }
+
+            Abi::C { unwind } => self.default_adjusted_cabi.unwrap_or(Abi::C { unwind }),
+
             abi => abi,
         }
     }
@@ -1742,6 +1749,16 @@ impl Target {
                     }
                 }
             } );
+            ($key_name:ident, Option<Abi>) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.find(&name[..]).and_then(|o| o.as_string().and_then(|s| {
+                    match lookup_abi(s) {
+                        Some(abi) => base.$key_name = Some(abi),
+                        _ => return Some(Err(format!("'{}' is not a valid value for abi", s))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
         }
 
         if let Some(s) = obj.find("target-endian").and_then(Json::as_string) {
@@ -1841,6 +1858,7 @@ impl Target {
         key!(has_thumb_interworking, bool);
         key!(split_debuginfo, SplitDebuginfo)?;
         key!(supported_sanitizers, SanitizerSet)?;
+        key!(default_adjusted_cabi, Option<Abi>)?;
 
         // NB: The old name is deprecated, but support for it is retained for
         // compatibility.
@@ -2081,6 +2099,10 @@ impl ToJson for Target {
         target_option_val!(split_debuginfo);
         target_option_val!(supported_sanitizers);
 
+        if let Some(abi) = self.default_adjusted_cabi {
+            d.insert("default-adjusted-cabi".to_string(), Abi::name(abi).to_json());
+        }
+
         if default.unsupported_abis != self.unsupported_abis {
             d.insert(
                 "unsupported-abis".to_string(),