Rollup merge of rust-lang#127605 - nikic:remove-extern-wasm, r=oli-obk

Remove extern "wasm" ABI

Remove the unstable `extern "wasm"` ABI (`wasm_abi` feature tracked in rust-lang#83788).

As discussed in rust-lang#127513 (comment) and following, this ABI is a failed experiment that did not end up being used for anything. Keeping support for this ABI in LLVM 19 would require us to switch wasm targets to the `experimental-mv` ABI, which we do not want to do.

It should be noted that `Abi::Wasm` was internally used for two things: The `-Z wasm-c-abi=legacy` ABI that is still used by default on some wasm targets, and the `extern "wasm"` ABI. Despite both being `Abi::Wasm` internally, they were not the same. An explicit `extern "wasm"` additionally enabled the `+multivalue` feature.

I've opted to remove `Abi::Wasm` in this patch entirely, instead of keeping it as an ABI with only internal usage. Both `-Z wasm-c-abi` variants are now treated as part of the normal C ABI, just with different different treatment in
adjust_for_foreign_abi.

Author: matthiaskrgr

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -6,7 +6,6 @@ use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, PatchableFuncti
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::config::{FunctionReturn, OptLevel};
 use rustc_span::symbol::sym;
-use rustc_target::spec::abi::Abi;
 use rustc_target::spec::{FramePointer, SanitizerSet, StackProbeType, StackProtector};
 use smallvec::SmallVec;
 
@@ -482,7 +481,7 @@ pub fn from_fn_attrs<'ll, 'tcx>(
         return;
     }
 
-    let mut function_features = function_features
+    let function_features = function_features
         .iter()
         .flat_map(|feat| {
             llvm_util::to_llvm_features(cx.tcx.sess, feat).into_iter().map(|f| format!("+{f}"))
@@ -504,17 +503,6 @@ pub fn from_fn_attrs<'ll, 'tcx>(
             let name = name.as_str();
             to_add.push(llvm::CreateAttrStringValue(cx.llcx, "wasm-import-name", 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_like(instance.def_id()) {
-            let abi = cx.tcx.fn_sig(instance.def_id()).skip_binder().abi();
-            if abi == Abi::Wasm {
-                function_features.push("+multivalue".to_string());
-            }
-        }
     }
 
     let global_features = cx.tcx.global_backend_features(()).iter().map(|s| s.as_str());

compiler/rustc_feature/src/removed.rs

@@ -215,6 +215,9 @@ declare_features! (
     /// Permits specifying whether a function should permit unwinding or abort on unwind.
     (removed, unwind_attributes, "1.56.0", Some(58760), Some("use the C-unwind ABI instead")),
     (removed, visible_private_types, "1.0.0", None, None),
+    /// Allows `extern "wasm" fn`
+    (removed, wasm_abi, "CURRENT_RUSTC_VERSION", Some(83788),
+     Some("non-standard wasm ABI is no longer supported")),
     // !!!!    !!!!    !!!!    !!!!   !!!!    !!!!    !!!!    !!!!    !!!!    !!!!    !!!!
     // Features are listed in alphabetical order. Tidy will fail if you don't keep it this way.
     // !!!!    !!!!    !!!!    !!!!   !!!!    !!!!    !!!!    !!!!    !!!!    !!!!    !!!!

compiler/rustc_feature/src/unstable.rs

@@ -640,8 +640,6 @@ declare_features! (
     (unstable, unsized_tuple_coercion, "1.20.0", Some(42877)),
     /// Allows using the `#[used(linker)]` (or `#[used(compiler)]`) attribute.
     (unstable, used_with_arg, "1.60.0", Some(93798)),
-    /// Allows `extern "wasm" fn`
-    (unstable, wasm_abi, "1.53.0", Some(83788)),
     /// Allows `do yeet` expressions
     (unstable, yeet_expr, "1.62.0", Some(96373)),
     // !!!!    !!!!    !!!!    !!!!   !!!!    !!!!    !!!!    !!!!    !!!!    !!!!    !!!!

compiler/rustc_middle/src/ty/layout.rs

@@ -1212,7 +1212,6 @@ pub fn fn_can_unwind(tcx: TyCtxt<'_>, fn_def_id: Option<DefId>, abi: SpecAbi) ->
         | RiscvInterruptM
         | RiscvInterruptS
         | CCmseNonSecureCall
-        | Wasm
         | Unadjusted => false,
         Rust | RustCall | RustCold | RustIntrinsic => {
             tcx.sess.panic_strategy() == PanicStrategy::Unwind

compiler/rustc_smir/src/rustc_internal/internal.rs

@@ -466,7 +466,6 @@ impl RustcInternal for Abi {
             Abi::AvrInterrupt => rustc_target::spec::abi::Abi::AvrInterrupt,
             Abi::AvrNonBlockingInterrupt => rustc_target::spec::abi::Abi::AvrNonBlockingInterrupt,
             Abi::CCmseNonSecureCall => rustc_target::spec::abi::Abi::CCmseNonSecureCall,
-            Abi::Wasm => rustc_target::spec::abi::Abi::Wasm,
             Abi::System { unwind } => rustc_target::spec::abi::Abi::System { unwind },
             Abi::RustIntrinsic => rustc_target::spec::abi::Abi::RustIntrinsic,
             Abi::RustCall => rustc_target::spec::abi::Abi::RustCall,

compiler/rustc_smir/src/rustc_smir/convert/ty.rs

@@ -909,7 +909,6 @@ impl<'tcx> Stable<'tcx> for rustc_target::spec::abi::Abi {
             abi::Abi::AvrInterrupt => Abi::AvrInterrupt,
             abi::Abi::AvrNonBlockingInterrupt => Abi::AvrNonBlockingInterrupt,
             abi::Abi::CCmseNonSecureCall => Abi::CCmseNonSecureCall,
-            abi::Abi::Wasm => Abi::Wasm,
             abi::Abi::System { unwind } => Abi::System { unwind },
             abi::Abi::RustIntrinsic => Abi::RustIntrinsic,
             abi::Abi::RustCall => Abi::RustCall,

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

@@ -1,6 +1,6 @@
 use crate::abi::{self, Abi, Align, FieldsShape, Size};
 use crate::abi::{HasDataLayout, TyAbiInterface, TyAndLayout};
-use crate::spec::{self, HasTargetSpec, HasWasmCAbiOpt};
+use crate::spec::{self, HasTargetSpec, HasWasmCAbiOpt, WasmCAbi};
 use rustc_macros::HashStable_Generic;
 use rustc_span::Symbol;
 use std::fmt;
@@ -854,7 +854,8 @@ impl<'a, Ty> FnAbi<'a, Ty> {
             return Ok(());
         }
 
-        match &cx.target_spec().arch[..] {
+        let spec = cx.target_spec();
+        match &spec.arch[..] {
             "x86" => {
                 let flavor = if let spec::abi::Abi::Fastcall { .. }
                 | spec::abi::Abi::Vectorcall { .. } = abi
@@ -901,9 +902,7 @@ impl<'a, Ty> FnAbi<'a, Ty> {
             "sparc" => sparc::compute_abi_info(cx, self),
             "sparc64" => sparc64::compute_abi_info(cx, self),
             "nvptx64" => {
-                if cx.target_spec().adjust_abi(cx, abi, self.c_variadic)
-                    == spec::abi::Abi::PtxKernel
-                {
+                if cx.target_spec().adjust_abi(abi, self.c_variadic) == spec::abi::Abi::PtxKernel {
                     nvptx64::compute_ptx_kernel_abi_info(cx, self)
                 } else {
                     nvptx64::compute_abi_info(self)
@@ -912,13 +911,14 @@ impl<'a, Ty> FnAbi<'a, Ty> {
             "hexagon" => hexagon::compute_abi_info(self),
             "xtensa" => xtensa::compute_abi_info(cx, self),
             "riscv32" | "riscv64" => riscv::compute_abi_info(cx, self),
-            "wasm32" | "wasm64" => {
-                if cx.target_spec().adjust_abi(cx, abi, self.c_variadic) == spec::abi::Abi::Wasm {
+            "wasm32" => {
+                if spec.os == "unknown" && cx.wasm_c_abi_opt() == WasmCAbi::Legacy {
                     wasm::compute_wasm_abi_info(self)
                 } else {
                     wasm::compute_c_abi_info(cx, self)
                 }
             }
+            "wasm64" => wasm::compute_c_abi_info(cx, self),
             "bpf" => bpf::compute_abi_info(self),
             arch => {
                 return Err(AdjustForForeignAbiError::Unsupported {

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

@@ -48,7 +48,6 @@ pub enum Abi {
     AvrInterrupt,
     AvrNonBlockingInterrupt,
     CCmseNonSecureCall,
-    Wasm,
     System {
         unwind: bool,
     },
@@ -123,7 +122,6 @@ const AbiDatas: &[AbiData] = &[
     AbiData { abi: Abi::AvrInterrupt, name: "avr-interrupt" },
     AbiData { abi: Abi::AvrNonBlockingInterrupt, name: "avr-non-blocking-interrupt" },
     AbiData { abi: Abi::CCmseNonSecureCall, name: "C-cmse-nonsecure-call" },
-    AbiData { abi: Abi::Wasm, name: "wasm" },
     AbiData { abi: Abi::System { unwind: false }, name: "system" },
     AbiData { abi: Abi::System { unwind: true }, name: "system-unwind" },
     AbiData { abi: Abi::RustIntrinsic, name: "rust-intrinsic" },
@@ -149,6 +147,9 @@ pub fn lookup(name: &str) -> Result<Abi, AbiUnsupported> {
         "riscv-interrupt-u" => AbiUnsupported::Reason {
             explain: "user-mode interrupt handlers have been removed from LLVM pending standardization, see: https://reviews.llvm.org/D149314",
         },
+        "wasm" => AbiUnsupported::Reason {
+            explain: "non-standard wasm ABI is no longer supported",
+        },
 
         _ => AbiUnsupported::Unrecognized,
 
@@ -241,10 +242,6 @@ pub fn is_stable(name: &str) -> Result<(), AbiDisabled> {
             feature: sym::abi_c_cmse_nonsecure_call,
             explain: "C-cmse-nonsecure-call ABI is experimental and subject to change",
         }),
-        "wasm" => Err(AbiDisabled::Unstable {
-            feature: sym::wasm_abi,
-            explain: "wasm ABI is experimental and subject to change",
-        }),
         _ => Err(AbiDisabled::Unrecognized),
     }
 }
@@ -287,16 +284,15 @@ impl Abi {
             AvrInterrupt => 23,
             AvrNonBlockingInterrupt => 24,
             CCmseNonSecureCall => 25,
-            Wasm => 26,
             // Cross-platform ABIs
-            System { unwind: false } => 27,
-            System { unwind: true } => 28,
-            RustIntrinsic => 29,
-            RustCall => 30,
-            Unadjusted => 31,
-            RustCold => 32,
-            RiscvInterruptM => 33,
-            RiscvInterruptS => 34,
+            System { unwind: false } => 26,
+            System { unwind: true } => 27,
+            RustIntrinsic => 28,
+            RustCall => 29,
+            Unadjusted => 30,
+            RustCold => 31,
+            RiscvInterruptM => 32,
+            RiscvInterruptS => 33,
         };
         debug_assert!(
             AbiDatas

compiler/rustc_target/src/spec/mod.rs

@@ -2608,22 +2608,8 @@ impl DerefMut for Target {
 
 impl Target {
     /// Given a function ABI, turn it into the correct ABI for this target.
-    pub fn adjust_abi<C>(&self, cx: &C, abi: Abi, c_variadic: bool) -> Abi
-    where
-        C: HasWasmCAbiOpt,
-    {
+    pub fn adjust_abi(&self, abi: Abi, c_variadic: bool) -> Abi {
         match abi {
-            Abi::C { .. } => {
-                if self.arch == "wasm32"
-                    && self.os == "unknown"
-                    && cx.wasm_c_abi_opt() == WasmCAbi::Legacy
-                {
-                    Abi::Wasm
-                } else {
-                    abi
-                }
-            }
-
             // On Windows, `extern "system"` behaves like msvc's `__stdcall`.
             // `__stdcall` only applies on x86 and on non-variadic functions:
             // https://learn.microsoft.com/en-us/cpp/cpp/stdcall?view=msvc-170
@@ -2676,7 +2662,6 @@ impl Target {
             Msp430Interrupt => self.arch == "msp430",
             RiscvInterruptM | RiscvInterruptS => ["riscv32", "riscv64"].contains(&&self.arch[..]),
             AvrInterrupt | AvrNonBlockingInterrupt => self.arch == "avr",
-            Wasm => ["wasm32", "wasm64"].contains(&&self.arch[..]),
             Thiscall { .. } => self.arch == "x86",
             // On windows these fall-back to platform native calling convention (C) when the
             // architecture is not supported.

compiler/rustc_ty_utils/src/abi.rs

@@ -324,7 +324,7 @@ fn fn_sig_for_fn_abi<'tcx>(
 #[inline]
 fn conv_from_spec_abi(tcx: TyCtxt<'_>, abi: SpecAbi, c_variadic: bool) -> Conv {
     use rustc_target::spec::abi::Abi::*;
-    match tcx.sess.target.adjust_abi(&tcx, abi, c_variadic) {
+    match tcx.sess.target.adjust_abi(abi, c_variadic) {
         RustIntrinsic | Rust | RustCall => Conv::Rust,
 
         // This is intentionally not using `Conv::Cold`, as that has to preserve
@@ -352,7 +352,6 @@ fn conv_from_spec_abi(tcx: TyCtxt<'_>, abi: SpecAbi, c_variadic: bool) -> Conv {
         AvrNonBlockingInterrupt => Conv::AvrNonBlockingInterrupt,
         RiscvInterruptM => Conv::RiscvInterrupt { kind: RiscvInterruptKind::Machine },
         RiscvInterruptS => Conv::RiscvInterrupt { kind: RiscvInterruptKind::Supervisor },
-        Wasm => Conv::C,
 
         // These API constants ought to be more specific...
         Cdecl { .. } => Conv::C,