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Remove extern "wasm" ABI
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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.
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nikic committed Jul 11, 2024
1 parent 0fdfb61 commit 8a50bcb
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Showing 25 changed files with 87 additions and 382 deletions.
14 changes: 1 addition & 13 deletions compiler/rustc_codegen_llvm/src/attributes.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down Expand Up @@ -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}"))
Expand All @@ -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());
Expand Down
3 changes: 3 additions & 0 deletions compiler/rustc_feature/src/removed.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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.
// !!!! !!!! !!!! !!!! !!!! !!!! !!!! !!!! !!!! !!!! !!!!
Expand Down
2 changes: 0 additions & 2 deletions compiler/rustc_feature/src/unstable.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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)),
// !!!! !!!! !!!! !!!! !!!! !!!! !!!! !!!! !!!! !!!! !!!!
Expand Down
1 change: 0 additions & 1 deletion compiler/rustc_middle/src/ty/layout.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down
1 change: 0 additions & 1 deletion compiler/rustc_smir/src/rustc_internal/internal.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand Down
1 change: 0 additions & 1 deletion compiler/rustc_smir/src/rustc_smir/convert/ty.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand Down
14 changes: 7 additions & 7 deletions compiler/rustc_target/src/abi/call/mod.rs
Original file line number Diff line number Diff line change
@@ -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;
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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)
Expand All @@ -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 {
Expand Down
26 changes: 11 additions & 15 deletions compiler/rustc_target/src/spec/abi/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,6 @@ pub enum Abi {
AvrInterrupt,
AvrNonBlockingInterrupt,
CCmseNonSecureCall,
Wasm,
System {
unwind: bool,
},
Expand Down Expand Up @@ -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" },
Expand All @@ -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,

Expand Down Expand Up @@ -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),
}
}
Expand Down Expand Up @@ -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
Expand Down
17 changes: 1 addition & 16 deletions compiler/rustc_target/src/spec/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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.
Expand Down
3 changes: 1 addition & 2 deletions compiler/rustc_ty_utils/src/abi.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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,
Expand Down
1 change: 0 additions & 1 deletion compiler/stable_mir/src/ty.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1045,7 +1045,6 @@ pub enum Abi {
AvrInterrupt,
AvrNonBlockingInterrupt,
CCmseNonSecureCall,
Wasm,
System { unwind: bool },
RustIntrinsic,
RustCall,
Expand Down
87 changes: 0 additions & 87 deletions tests/run-make/wasm-abi/foo.rs

This file was deleted.

22 changes: 0 additions & 22 deletions tests/run-make/wasm-abi/host.wat

This file was deleted.

29 changes: 0 additions & 29 deletions tests/run-make/wasm-abi/rmake.rs

This file was deleted.

4 changes: 4 additions & 0 deletions tests/ui/abi/removed-wasm-abi.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
extern "wasm" fn test() {}
//~^ ERROR invalid ABI: found `wasm`

fn main() {}
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