fix ZST handling for Windows ABIs on MSVC target

compiler/rustc_abi/src/extern_abi/mod.rs

@@ -192,6 +192,10 @@ pub fn is_enabled(
     s
 }
 
+/// Returns whether the ABI is stable to use.
+///
+/// Note that there is a separate check determining whether the ABI is even supported
+/// on the current target; see `fn is_abi_supported` in `rustc_target::spec`.
 pub fn is_stable(name: &str) -> Result<(), AbiDisabled> {
     match name {
         // Stable

compiler/rustc_target/src/callconv/mod.rs

@@ -1,7 +1,7 @@
 use std::str::FromStr;
 use std::{fmt, iter};
 
-pub use rustc_abi::{Reg, RegKind};
+pub use rustc_abi::{ExternAbi, Reg, RegKind};
 use rustc_macros::HashStable_Generic;
 use rustc_span::Symbol;
 
@@ -9,8 +9,7 @@ use crate::abi::{
     self, AddressSpace, Align, BackendRepr, HasDataLayout, Pointer, Size, TyAbiInterface,
     TyAndLayout,
 };
-use crate::spec::abi::Abi as SpecAbi;
+use crate::spec::{HasTargetSpec, HasWasmCAbiOpt, HasX86AbiOpt, WasmCAbi};
-use crate::spec::{self, HasTargetSpec, HasWasmCAbiOpt, HasX86AbiOpt, WasmCAbi};
 
 mod aarch64;
 mod amdgpu;
@@ -627,20 +626,20 @@ impl<'a, Ty: fmt::Display> fmt::Debug for FnAbi<'a, Ty> {
 #[derive(Copy, Clone, Debug, HashStable_Generic)]
 pub enum AdjustForForeignAbiError {
     /// Target architecture doesn't support "foreign" (i.e. non-Rust) ABIs.
-    Unsupported { arch: Symbol, abi: spec::abi::Abi },
+    Unsupported { arch: Symbol, abi: ExternAbi },
 }
 
 impl<'a, Ty> FnAbi<'a, Ty> {
     pub fn adjust_for_foreign_abi<C>(
         &mut self,
         cx: &C,
-        abi: spec::abi::Abi,
+        abi: ExternAbi,
     ) -> Result<(), AdjustForForeignAbiError>
     where
         Ty: TyAbiInterface<'a, C> + Copy,
         C: HasDataLayout + HasTargetSpec + HasWasmCAbiOpt + HasX86AbiOpt,
     {
-        if abi == spec::abi::Abi::X86Interrupt {
+        if abi == ExternAbi::X86Interrupt {
             if let Some(arg) = self.args.first_mut() {
                 arg.pass_by_stack_offset(None);
             }
@@ -651,12 +650,10 @@ impl<'a, Ty> FnAbi<'a, Ty> {
         match &spec.arch[..] {
             "x86" => {
                 let (flavor, regparm) = match abi {
-                    spec::abi::Abi::Fastcall { .. } | spec::abi::Abi::Vectorcall { .. } => {
+                    ExternAbi::Fastcall { .. } | ExternAbi::Vectorcall { .. } => {
                         (x86::Flavor::FastcallOrVectorcall, None)
                     }
-                    spec::abi::Abi::C { .. }
+                    ExternAbi::C { .. } | ExternAbi::Cdecl { .. } | ExternAbi::Stdcall { .. } => {
-                    | spec::abi::Abi::Cdecl { .. }
-                    | spec::abi::Abi::Stdcall { .. } => {
                         (x86::Flavor::General, cx.x86_abi_opt().regparm)
                     }
                     _ => (x86::Flavor::General, None),
@@ -666,11 +663,13 @@ impl<'a, Ty> FnAbi<'a, Ty> {
                 x86::compute_abi_info(cx, self, opts);
             }
             "x86_64" => match abi {
-                spec::abi::Abi::SysV64 { .. } => x86_64::compute_abi_info(cx, self),
+                ExternAbi::SysV64 { .. } => x86_64::compute_abi_info(cx, self),
-                spec::abi::Abi::Win64 { .. } => x86_win64::compute_abi_info(cx, self),
+                ExternAbi::Win64 { .. } | ExternAbi::Vectorcall { .. } => {
+                    x86_win64::compute_abi_info(cx, self, abi)
+                }
                 _ => {
                     if cx.target_spec().is_like_windows {
-                        x86_win64::compute_abi_info(cx, self)
+                        x86_win64::compute_abi_info(cx, self, abi)
                     } else {
                         x86_64::compute_abi_info(cx, self)
                     }
@@ -701,7 +700,7 @@ 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(abi, self.c_variadic) == spec::abi::Abi::PtxKernel {
+                if cx.target_spec().adjust_abi(abi, self.c_variadic) == ExternAbi::PtxKernel {
                     nvptx64::compute_ptx_kernel_abi_info(cx, self)
                 } else {
                     nvptx64::compute_abi_info(self)
@@ -730,7 +729,7 @@ impl<'a, Ty> FnAbi<'a, Ty> {
         Ok(())
     }
 
-    pub fn adjust_for_rust_abi<C>(&mut self, cx: &C, abi: SpecAbi)
+    pub fn adjust_for_rust_abi<C>(&mut self, cx: &C, abi: ExternAbi)
     where
         Ty: TyAbiInterface<'a, C> + Copy,
         C: HasDataLayout + HasTargetSpec,
@@ -821,7 +820,7 @@ impl<'a, Ty> FnAbi<'a, Ty> {
                 // that's how we connect up to LLVM and it's unstable
                 // anyway, we control all calls to it in libstd.
                 BackendRepr::Vector { .. }
-                    if abi != SpecAbi::RustIntrinsic && spec.simd_types_indirect =>
+                    if abi != ExternAbi::RustIntrinsic && spec.simd_types_indirect =>
                 {
                     arg.make_indirect();
                     continue;

compiler/rustc_target/src/callconv/x86_win64.rs

@@ -1,11 +1,15 @@
-use rustc_abi::{BackendRepr, Float, Primitive};
+use rustc_abi::{BackendRepr, ExternAbi, Float, Primitive};
 
 use crate::abi::call::{ArgAbi, FnAbi, Reg};
 use crate::spec::HasTargetSpec;
 
 // Win64 ABI: https://docs.microsoft.com/en-us/cpp/build/parameter-passing
 
-pub(crate) fn compute_abi_info<Ty>(cx: &impl HasTargetSpec, fn_abi: &mut FnAbi<'_, Ty>) {
+pub(crate) fn compute_abi_info<Ty>(
+    cx: &impl HasTargetSpec,
+    fn_abi: &mut FnAbi<'_, Ty>,
+    abi: ExternAbi,
+) {
     let fixup = |a: &mut ArgAbi<'_, Ty>| {
         match a.layout.backend_repr {
             BackendRepr::Uninhabited | BackendRepr::Memory { sized: false } => {}
@@ -40,11 +44,15 @@ pub(crate) fn compute_abi_info<Ty>(cx: &impl HasTargetSpec, fn_abi: &mut FnAbi<'
         fixup(&mut fn_abi.ret);
     }
     for arg in fn_abi.args.iter_mut() {
-        if arg.is_ignore() {
+        if arg.is_ignore() && arg.layout.is_zst() {
-            // x86_64-pc-windows-gnu doesn't ignore ZSTs.
+            // Windows ABIs do not talk about ZST since such types do not exist in MSVC.
-            if cx.target_spec().os == "windows"
+            // In that sense we can do whatever we want here, and maybe we should throw an error
-                && cx.target_spec().env == "gnu"
+            // (but of course that would be a massive breaking change now).
-                && arg.layout.is_zst()
+            // We try to match clang and gcc, so we make windows-gnu and the native
+            // Windows ABIs (i.e., everything except for `extern "C"`) pass ZST via
+            // pointer indirection. windows-msvc `extern "C"` still skips ZST.
+            if (cx.target_spec().os == "windows" && cx.target_spec().env == "gnu")
+                || !matches!(abi, ExternAbi::C { .. })
             {
                 arg.make_indirect_from_ignore();
             }

compiler/rustc_target/src/spec/mod.rs

@@ -2815,12 +2815,17 @@ impl Target {
             Abi::EfiApi if self.arch == "x86_64" => Abi::Win64 { unwind: false },
             Abi::EfiApi => Abi::C { unwind: false },
 
-            // See commentary in `is_abi_supported`.
+            // See commentary in `is_abi_supported`: we map these ABIs to "C" when they do not make sense.
-            Abi::Stdcall { .. } | Abi::Thiscall { .. } if self.arch == "x86" => abi,
+            Abi::Stdcall { .. } | Abi::Thiscall { .. } | Abi::Fastcall { .. }
-            Abi::Stdcall { unwind } | Abi::Thiscall { unwind } => Abi::C { unwind },
+                if self.arch == "x86" =>
-            Abi::Fastcall { .. } if self.arch == "x86" => abi,
+            {
+                abi
+            }
             Abi::Vectorcall { .. } if ["x86", "x86_64"].contains(&&self.arch[..]) => abi,
-            Abi::Fastcall { unwind } | Abi::Vectorcall { unwind } => Abi::C { unwind },
+            Abi::Stdcall { unwind }
+            | Abi::Thiscall { unwind }
+            | Abi::Fastcall { unwind }
+            | Abi::Vectorcall { unwind } => Abi::C { unwind },
 
             // The Windows x64 calling convention we use for `extern "Rust"`
             // <https://learn.microsoft.com/en-us/cpp/build/x64-software-conventions#register-volatility-and-preservation>

compiler/rustc_ty_utils/src/abi.rs

@@ -267,8 +267,10 @@ fn fn_sig_for_fn_abi<'tcx>(
 
 #[inline]
 fn conv_from_spec_abi(tcx: TyCtxt<'_>, abi: ExternAbi, c_variadic: bool) -> Conv {
+    let target = &tcx.sess.target;
+
     use rustc_abi::ExternAbi::*;
-    match tcx.sess.target.adjust_abi(abi, c_variadic) {
+    match target.adjust_abi(abi, c_variadic) {
         RustIntrinsic | Rust | RustCall => Conv::Rust,
 
         // This is intentionally not using `Conv::Cold`, as that has to preserve
@@ -279,10 +281,37 @@ fn conv_from_spec_abi(tcx: TyCtxt<'_>, abi: ExternAbi, c_variadic: bool) -> Conv
         System { .. } => bug!("system abi should be selected elsewhere"),
         EfiApi => bug!("eficall abi should be selected elsewhere"),
 
-        Stdcall { .. } => Conv::X86Stdcall,
+        // See commentary in `is_abi_supported`: we map these to "C" on targets
-        Fastcall { .. } => Conv::X86Fastcall,
+        // where they do not make sense.
-        Vectorcall { .. } => Conv::X86VectorCall,
+        Stdcall { .. } => {
-        Thiscall { .. } => Conv::X86ThisCall,
+            if target.arch == "x86" {
+                Conv::X86Stdcall
+            } else {
+                Conv::C
+            }
+        }
+        Fastcall { .. } => {
+            if target.arch == "x86" {
+                Conv::X86Fastcall
+            } else {
+                Conv::C
+            }
+        }
+        Vectorcall { .. } => {
+            if ["x86", "x86_64"].contains(&&target.arch[..]) {
+                Conv::X86VectorCall
+            } else {
+                Conv::C
+            }
+        }
+        Thiscall { .. } => {
+            if target.arch == "x86" {
+                Conv::X86ThisCall
+            } else {
+                Conv::C
+            }
+        }
+
         C { .. } => Conv::C,
         Unadjusted => Conv::C,
         Win64 { .. } => Conv::X86_64Win64,

tests/codegen/abi-win64-zst.rs

@@ -0,0 +1,52 @@
+//@ compile-flags: -Z merge-functions=disabled
+
+//@ revisions: windows-gnu
+//@[windows-gnu] compile-flags: --target x86_64-pc-windows-gnu
+//@[windows-gnu] needs-llvm-components: x86
+
+//@ revisions: windows-msvc
+//@[windows-msvc] compile-flags: --target x86_64-pc-windows-msvc
+//@[windows-msvc] needs-llvm-components: x86
+
+// Also test what happens when using a Windows ABI on Linux.
+//@ revisions: linux
+//@[linux] compile-flags: --target x86_64-unknown-linux-gnu
+//@[linux] needs-llvm-components: x86
+
+#![feature(no_core, lang_items, rustc_attrs, abi_vectorcall)]
+#![no_core]
+#![crate_type = "lib"]
+
+#[lang = "sized"]
+trait Sized {}
+
+// Make sure the argument is always passed when explicitly requesting a Windows ABI.
+// Our goal here is to match clang: <https://clang.godbolt.org/z/Wr4jMWq3P>.
+
+// CHECK: define win64cc void @pass_zst_win64(ptr {{.*}})
+#[no_mangle]
+extern "win64" fn pass_zst_win64(_: ()) {}
+
+// CHECK: define x86_vectorcallcc void @pass_zst_vectorcall(ptr {{.*}})
+#[no_mangle]
+extern "vectorcall" fn pass_zst_vectorcall(_: ()) {}
+
+// windows-gnu: define void @pass_zst_fastcall(ptr {{.*}})
+// windows-msvc: define void @pass_zst_fastcall(ptr {{.*}})
+#[no_mangle]
+#[cfg(windows)] // "fastcall" is not valid on 64bit Linux
+extern "fastcall" fn pass_zst_fastcall(_: ()) {}
+
+// The sysv64 ABI ignores ZST.
+
+// CHECK: define x86_64_sysvcc void @pass_zst_sysv64()
+#[no_mangle]
+extern "sysv64" fn pass_zst_sysv64(_: ()) {}
+
+// For `extern "C"` functions, ZST are ignored on windows-msvc.
+
+// linux: define void @pass_zst_c()
+// windows-msvc: define void @pass_zst_c()
+// windows-gnu: define void @pass_zst_c(ptr {{.*}})
+#[no_mangle]
+extern "C" fn pass_zst_c(_: ()) {}

tests/ui/abi/win64-zst.rs

@@ -1,24 +0,0 @@
-//@ normalize-stderr: "(abi|pref|unadjusted_abi_align): Align\([1-8] bytes\)" -> "$1: $$SOME_ALIGN"
-//@ only-x86_64
-
-//@ revisions: x86_64-linux
-//@[x86_64-linux] compile-flags: --target x86_64-unknown-linux-gnu
-//@[x86_64-linux] needs-llvm-components: x86
-
-//@ revisions: x86_64-windows-gnu
-//@[x86_64-windows-gnu] compile-flags: --target x86_64-pc-windows-gnu
-//@[x86_64-windows-gnu] needs-llvm-components: x86
-
-//@ revisions: x86_64-windows-msvc
-//@[x86_64-windows-msvc] compile-flags: --target x86_64-pc-windows-msvc
-//@[x86_64-windows-msvc] needs-llvm-components: x86
-
-#![feature(no_core, lang_items, rustc_attrs)]
-#![no_core]
-#![crate_type = "lib"]
-
-#[lang = "sized"]
-trait Sized {}
-
-#[rustc_abi(debug)]
-extern "win64" fn pass_zst(_: ()) {} //~ ERROR: fn_abi

tests/ui/abi/win64-zst.x86_64-linux.stderr

@@ -1,69 +0,0 @@
-error: fn_abi_of(pass_zst) = FnAbi {
-           args: [
-               ArgAbi {
-                   layout: TyAndLayout {
-                       ty: (),
-                       layout: Layout {
-                           size: Size(0 bytes),
-                           align: AbiAndPrefAlign {
-                               abi: $SOME_ALIGN,
-                               pref: $SOME_ALIGN,
-                           },
-                           abi: Memory {
-                               sized: true,
-                           },
-                           fields: Arbitrary {
-                               offsets: [],
-                               memory_index: [],
-                           },
-                           largest_niche: None,
-                           variants: Single {
-                               index: 0,
-                           },
-                           max_repr_align: None,
-                           unadjusted_abi_align: $SOME_ALIGN,
-                           randomization_seed: 0,
-                       },
-                   },
-                   mode: Ignore,
-               },
-           ],
-           ret: ArgAbi {
-               layout: TyAndLayout {
-                   ty: (),
-                   layout: Layout {
-                       size: Size(0 bytes),
-                       align: AbiAndPrefAlign {
-                           abi: $SOME_ALIGN,
-                           pref: $SOME_ALIGN,
-                       },
-                       abi: Memory {
-                           sized: true,
-                       },
-                       fields: Arbitrary {
-                           offsets: [],
-                           memory_index: [],
-                       },
-                       largest_niche: None,
-                       variants: Single {
-                           index: 0,
-                       },
-                       max_repr_align: None,
-                       unadjusted_abi_align: $SOME_ALIGN,
-                       randomization_seed: 0,
-                   },
-               },
-               mode: Ignore,
-           },
-           c_variadic: false,
-           fixed_count: 1,
-           conv: X86_64Win64,
-           can_unwind: false,
-       }
-  --> $DIR/win64-zst.rs:24:1
-   |
-LL | extern "win64" fn pass_zst(_: ()) {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to 1 previous error
-

tests/ui/abi/win64-zst.x86_64-windows-gnu.stderr

@@ -1,80 +0,0 @@
-error: fn_abi_of(pass_zst) = FnAbi {
-           args: [
-               ArgAbi {
-                   layout: TyAndLayout {
-                       ty: (),
-                       layout: Layout {
-                           size: Size(0 bytes),
-                           align: AbiAndPrefAlign {
-                               abi: $SOME_ALIGN,
-                               pref: $SOME_ALIGN,
-                           },
-                           abi: Memory {
-                               sized: true,
-                           },
-                           fields: Arbitrary {
-                               offsets: [],
-                               memory_index: [],
-                           },
-                           largest_niche: None,
-                           variants: Single {
-                               index: 0,
-                           },
-                           max_repr_align: None,
-                           unadjusted_abi_align: $SOME_ALIGN,
-                           randomization_seed: 0,
-                       },
-                   },
-                   mode: Indirect {
-                       attrs: ArgAttributes {
-                           regular: NoAlias | NoCapture | NonNull | NoUndef,
-                           arg_ext: None,
-                           pointee_size: Size(0 bytes),
-                           pointee_align: Some(
-                               Align(1 bytes),
-                           ),
-                       },
-                       meta_attrs: None,
-                       on_stack: false,
-                   },
-               },
-           ],
-           ret: ArgAbi {
-               layout: TyAndLayout {
-                   ty: (),
-                   layout: Layout {
-                       size: Size(0 bytes),
-                       align: AbiAndPrefAlign {
-                           abi: $SOME_ALIGN,
-                           pref: $SOME_ALIGN,
-                       },
-                       abi: Memory {
-                           sized: true,
-                       },
-                       fields: Arbitrary {
-                           offsets: [],
-                           memory_index: [],
-                       },
-                       largest_niche: None,
-                       variants: Single {
-                           index: 0,
-                       },
-                       max_repr_align: None,
-                       unadjusted_abi_align: $SOME_ALIGN,
-                       randomization_seed: 0,
-                   },
-               },
-               mode: Ignore,
-           },
-           c_variadic: false,
-           fixed_count: 1,
-           conv: X86_64Win64,
-           can_unwind: false,
-       }
-  --> $DIR/win64-zst.rs:24:1
-   |
-LL | extern "win64" fn pass_zst(_: ()) {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to 1 previous error
-

tests/ui/abi/win64-zst.x86_64-windows-msvc.stderr

@@ -1,69 +0,0 @@
-error: fn_abi_of(pass_zst) = FnAbi {
-           args: [
-               ArgAbi {
-                   layout: TyAndLayout {
-                       ty: (),
-                       layout: Layout {
-                           size: Size(0 bytes),
-                           align: AbiAndPrefAlign {
-                               abi: $SOME_ALIGN,
-                               pref: $SOME_ALIGN,
-                           },
-                           abi: Memory {
-                               sized: true,
-                           },
-                           fields: Arbitrary {
-                               offsets: [],
-                               memory_index: [],
-                           },
-                           largest_niche: None,
-                           variants: Single {
-                               index: 0,
-                           },
-                           max_repr_align: None,
-                           unadjusted_abi_align: $SOME_ALIGN,
-                           randomization_seed: 0,
-                       },
-                   },
-                   mode: Ignore,
-               },
-           ],
-           ret: ArgAbi {
-               layout: TyAndLayout {
-                   ty: (),
-                   layout: Layout {
-                       size: Size(0 bytes),
-                       align: AbiAndPrefAlign {
-                           abi: $SOME_ALIGN,
-                           pref: $SOME_ALIGN,
-                       },
-                       abi: Memory {
-                           sized: true,
-                       },
-                       fields: Arbitrary {
-                           offsets: [],
-                           memory_index: [],
-                       },
-                       largest_niche: None,
-                       variants: Single {
-                           index: 0,
-                       },
-                       max_repr_align: None,
-                       unadjusted_abi_align: $SOME_ALIGN,
-                       randomization_seed: 0,
-                   },
-               },
-               mode: Ignore,
-           },
-           c_variadic: false,
-           fixed_count: 1,
-           conv: X86_64Win64,
-           can_unwind: false,
-       }
-  --> $DIR/win64-zst.rs:24:1
-   |
-LL | extern "win64" fn pass_zst(_: ()) {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to 1 previous error
-