compiler: add AbiMap

- Add AbiMapping for encoding the nuance of deprecated ABIs

4 files changed, 190 insertions, 1 deletions

diff --git a/compiler/rustc_target/src/callconv/mod.rs b/compiler/rustc_target/src/callconv/mod.rs
index 907614520a2..5e510ef38be 100644
--- a/compiler/rustc_target/src/callconv/mod.rs
+++ b/compiler/rustc_target/src/callconv/mod.rs
@@ -8,6 +8,7 @@ use rustc_abi::{
 };
 use rustc_macros::HashStable_Generic;
 
+pub use crate::spec::AbiMap;
 use crate::spec::{HasTargetSpec, HasWasmCAbiOpt, HasX86AbiOpt, RustcAbi, WasmCAbi};
 
 mod aarch64;
diff --git a/compiler/rustc_target/src/spec/abi_map.rs b/compiler/rustc_target/src/spec/abi_map.rs
new file mode 100644
index 00000000000..d9101f79f04
--- /dev/null
+++ b/compiler/rustc_target/src/spec/abi_map.rs
@@ -0,0 +1,187 @@
+use rustc_abi::{ArmCall, CanonAbi, ExternAbi, InterruptKind, X86Call};
+
+use crate::spec::Target;
+
+/// Mapping for ExternAbi to CanonAbi according to a Target
+///
+/// A maybe-transitional structure circa 2025 for hosting future experiments in
+/// encapsulating arch-specific ABI lowering details to make them more testable.
+#[derive(Clone, Debug)]
+pub struct AbiMap {
+    arch: Arch,
+    os: OsKind,
+}
+
+#[derive(Copy, Clone, Debug)]
+pub enum AbiMapping {
+    /// this ABI is exactly mapped for this platform
+    Direct(CanonAbi),
+    /// we don't yet warn on this, but we will
+    Deprecated(CanonAbi),
+    Invalid,
+}
+
+impl AbiMapping {
+    pub fn into_option(self) -> Option<CanonAbi> {
+        match self {
+            Self::Direct(abi) | Self::Deprecated(abi) => Some(abi),
+            Self::Invalid => None,
+        }
+    }
+
+    pub fn unwrap(self) -> CanonAbi {
+        self.into_option().unwrap()
+    }
+
+    pub fn is_mapped(self) -> bool {
+        self.into_option().is_some()
+    }
+}
+
+impl AbiMap {
+    pub fn from_target(target: &Target) -> Self {
+        // the purpose of this little exercise is to force listing what affects these mappings
+        let arch = match &*target.arch {
+            "aarch64" => Arch::Aarch64,
+            "amdgpu" => Arch::Amdgpu,
+            "arm" if target.llvm_target.starts_with("thumbv8m") => Arch::Arm(ArmVer::ThumbV8M),
+            "arm" => Arch::Arm(ArmVer::Other),
+            "avr" => Arch::Avr,
+            "msp430" => Arch::Msp430,
+            "nvptx64" => Arch::Nvptx,
+            "riscv32" | "riscv64" => Arch::Riscv,
+            "x86" => Arch::X86,
+            "x86_64" => Arch::X86_64,
+            _ => Arch::Other,
+        };
+        let os = if target.is_like_windows { OsKind::Windows } else { OsKind::Other };
+        AbiMap { arch, os }
+    }
+
+    pub fn canonize_abi(&self, extern_abi: ExternAbi, has_c_varargs: bool) -> AbiMapping {
+        let AbiMap { os, arch } = *self;
+
+        let canon_abi = match (extern_abi, arch) {
+            // infallible lowerings
+            (ExternAbi::C { .. }, _) => CanonAbi::C,
+            (ExternAbi::Rust | ExternAbi::RustCall, _) => CanonAbi::Rust,
+            (ExternAbi::Unadjusted, _) => CanonAbi::C,
+
+            (ExternAbi::RustCold, _) if self.os == OsKind::Windows => CanonAbi::Rust,
+            (ExternAbi::RustCold, _) => CanonAbi::RustCold,
+
+            (ExternAbi::System { .. }, Arch::X86) if os == OsKind::Windows && !has_c_varargs => {
+                CanonAbi::X86(X86Call::Stdcall)
+            }
+            (ExternAbi::System { .. }, _) => CanonAbi::C,
+
+            // fallible lowerings
+            (ExternAbi::EfiApi, Arch::Arm(..)) => CanonAbi::Arm(ArmCall::Aapcs),
+            (ExternAbi::EfiApi, Arch::X86_64) => CanonAbi::X86(X86Call::Win64),
+            (ExternAbi::EfiApi, Arch::Aarch64 | Arch::Riscv | Arch::X86) => CanonAbi::C,
+            (ExternAbi::EfiApi, _) => return AbiMapping::Invalid,
+
+            (ExternAbi::Aapcs { .. }, Arch::Arm(..)) => CanonAbi::Arm(ArmCall::Aapcs),
+            (ExternAbi::Aapcs { .. }, _) => return AbiMapping::Invalid,
+
+            (ExternAbi::CCmseNonSecureCall, Arch::Arm(ArmVer::ThumbV8M)) => {
+                CanonAbi::Arm(ArmCall::CCmseNonSecureCall)
+            }
+            (ExternAbi::CCmseNonSecureEntry, Arch::Arm(ArmVer::ThumbV8M)) => {
+                CanonAbi::Arm(ArmCall::CCmseNonSecureEntry)
+            }
+            (ExternAbi::CCmseNonSecureCall | ExternAbi::CCmseNonSecureEntry, ..) => {
+                return AbiMapping::Invalid;
+            }
+
+            (ExternAbi::Cdecl { .. }, Arch::X86) => CanonAbi::C,
+            (ExternAbi::Cdecl { .. }, _) => return AbiMapping::Deprecated(CanonAbi::C),
+
+            (ExternAbi::Fastcall { .. }, Arch::X86) => CanonAbi::X86(X86Call::Fastcall),
+            (ExternAbi::Fastcall { .. }, _) if os == OsKind::Windows => {
+                return AbiMapping::Deprecated(CanonAbi::C);
+            }
+            (ExternAbi::Fastcall { .. }, _) => return AbiMapping::Invalid,
+
+            (ExternAbi::Stdcall { .. }, Arch::X86) => CanonAbi::X86(X86Call::Stdcall),
+            (ExternAbi::Stdcall { .. }, _) if os == OsKind::Windows => {
+                return AbiMapping::Deprecated(CanonAbi::C);
+            }
+            (ExternAbi::Stdcall { .. }, _) => return AbiMapping::Invalid,
+
+            (ExternAbi::Thiscall { .. }, Arch::X86) => CanonAbi::X86(X86Call::Thiscall),
+            (ExternAbi::Thiscall { .. }, _) => return AbiMapping::Invalid,
+
+            (ExternAbi::Vectorcall { .. }, Arch::X86 | Arch::X86_64) => {
+                CanonAbi::X86(X86Call::Vectorcall)
+            }
+            (ExternAbi::Vectorcall { .. }, _) if os == OsKind::Windows => {
+                return AbiMapping::Deprecated(CanonAbi::C);
+            }
+            (ExternAbi::Vectorcall { .. }, _) => return AbiMapping::Invalid,
+
+            (ExternAbi::SysV64 { .. }, Arch::X86_64) => CanonAbi::X86(X86Call::SysV64),
+            (ExternAbi::Win64 { .. }, Arch::X86_64) => CanonAbi::X86(X86Call::Win64),
+            (ExternAbi::SysV64 { .. } | ExternAbi::Win64 { .. }, _) => return AbiMapping::Invalid,
+
+            (ExternAbi::PtxKernel, Arch::Nvptx) => CanonAbi::GpuKernel,
+            (ExternAbi::GpuKernel, Arch::Amdgpu | Arch::Nvptx) => CanonAbi::GpuKernel,
+            (ExternAbi::PtxKernel | ExternAbi::GpuKernel, _) => return AbiMapping::Invalid,
+
+            (ExternAbi::AvrInterrupt, Arch::Avr) => CanonAbi::Interrupt(InterruptKind::Avr),
+            (ExternAbi::AvrNonBlockingInterrupt, Arch::Avr) => {
+                CanonAbi::Interrupt(InterruptKind::AvrNonBlocking)
+            }
+            (ExternAbi::Msp430Interrupt, Arch::Msp430) => {
+                CanonAbi::Interrupt(InterruptKind::Msp430)
+            }
+            (ExternAbi::RiscvInterruptM, Arch::Riscv) => {
+                CanonAbi::Interrupt(InterruptKind::RiscvMachine)
+            }
+            (ExternAbi::RiscvInterruptS, Arch::Riscv) => {
+                CanonAbi::Interrupt(InterruptKind::RiscvSupervisor)
+            }
+            (ExternAbi::X86Interrupt, Arch::X86 | Arch::X86_64) => {
+                CanonAbi::Interrupt(InterruptKind::X86)
+            }
+            (
+                ExternAbi::AvrInterrupt
+                | ExternAbi::AvrNonBlockingInterrupt
+                | ExternAbi::Msp430Interrupt
+                | ExternAbi::RiscvInterruptM
+                | ExternAbi::RiscvInterruptS
+                | ExternAbi::X86Interrupt,
+                _,
+            ) => return AbiMapping::Invalid,
+        };
+
+        AbiMapping::Direct(canon_abi)
+    }
+}
+
+#[derive(Debug, PartialEq, Copy, Clone)]
+enum Arch {
+    Aarch64,
+    Amdgpu,
+    Arm(ArmVer),
+    Avr,
+    Msp430,
+    Nvptx,
+    Riscv,
+    X86,
+    X86_64,
+    /// Architectures which don't need other considerations for ABI lowering
+    Other,
+}
+
+#[derive(Debug, PartialEq, Copy, Clone)]
+enum OsKind {
+    Windows,
+    Other,
+}
+
+#[derive(Debug, PartialEq, Copy, Clone)]
+enum ArmVer {
+    ThumbV8M,
+    Other,
+}
diff --git a/compiler/rustc_target/src/spec/json.rs b/compiler/rustc_target/src/spec/json.rs
index be71da76b4a..82d1eea21cd 100644
--- a/compiler/rustc_target/src/spec/json.rs
+++ b/compiler/rustc_target/src/spec/json.rs
@@ -546,7 +546,6 @@ impl Target {
                 incorrect_type.push("frame-pointer".into())
             }
         }
-
         key!(c_int_width = "target-c-int-width");
         key!(c_enum_min_bits, Option<u64>); // if None, matches c_int_width
         key!(os);
diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
index 303be54a6d7..e45787a3a49 100644
--- a/compiler/rustc_target/src/spec/mod.rs
+++ b/compiler/rustc_target/src/spec/mod.rs
@@ -59,9 +59,11 @@ use crate::spec::crt_objects::CrtObjects;
 
 pub mod crt_objects;
 
+mod abi_map;
 mod base;
 mod json;
 
+pub use abi_map::AbiMap;
 pub use base::apple;
 pub use base::avr::ef_avr_arch;