rustc_target: add abi::call::Conv::Rust distinct from Conv::C.

src/librustc/ty/layout.rs

@@ -2441,7 +2441,7 @@ where
 
         use rustc_target::spec::abi::Abi::*;
         let conv = match cx.tcx().sess.target.target.adjust_abi(sig.abi) {
-            RustIntrinsic | PlatformIntrinsic | Rust | RustCall => Conv::C,
+            RustIntrinsic | PlatformIntrinsic | Rust | RustCall => Conv::Rust,
 
             // It's the ABI's job to select this, not ours.
             System => bug!("system abi should be selected elsewhere"),

src/librustc_codegen_llvm/abi.rs

@@ -372,7 +372,7 @@ impl<'tcx> FnAbiLlvmExt<'tcx> for FnAbi<'tcx, Ty<'tcx>> {
 
     fn llvm_cconv(&self) -> llvm::CallConv {
         match self.conv {
-            Conv::C => llvm::CCallConv,
+            Conv::C | Conv::Rust => llvm::CCallConv,
             Conv::AmdGpuKernel => llvm::AmdGpuKernel,
             Conv::ArmAapcs => llvm::ArmAapcsCallConv,
             Conv::Msp430Intr => llvm::Msp430Intr,

src/librustc_codegen_llvm/attributes.rs

@@ -6,15 +6,16 @@ use rustc::hir::CodegenFnAttrFlags;
 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
 use rustc::session::Session;
 use rustc::session::config::{Sanitizer, OptLevel};
-use rustc::ty::{self, TyCtxt};
+use rustc::ty::{self, TyCtxt, Ty};
 use rustc::ty::layout::HasTyCtxt;
 use rustc::ty::query::Providers;
 use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_data_structures::fx::FxHashMap;
+use rustc_target::abi::call::Conv;
 use rustc_target::spec::PanicStrategy;
 use rustc_codegen_ssa::traits::*;
 
-use crate::abi::Abi;
+use crate::abi::FnAbi;
 use crate::attributes;
 use crate::llvm::{self, Attribute};
 use crate::llvm::AttributePlace::Function;
@@ -203,6 +204,7 @@ pub fn from_fn_attrs(
     cx: &CodegenCx<'ll, 'tcx>,
     llfn: &'ll Value,
     instance: ty::Instance<'tcx>,
+    fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
 ) {
     let codegen_fn_attrs = cx.tcx.codegen_fn_attrs(instance.def_id());
 
@@ -279,10 +281,7 @@ pub fn from_fn_attrs(
         // Special attribute for allocator functions, which can't unwind.
         false
     } else {
-        // FIXME(eddyb) avoid this `Instance::fn_sig` call.
+        if fn_abi.conv == Conv::Rust {
-        // Perhaps store the relevant information in `FnAbi`?
-        let abi = instance.fn_sig(cx.tcx()).abi();
-        if abi == Abi::Rust || abi == Abi::RustCall {
             // Any Rust method (or `extern "Rust" fn` or `extern
             // "rust-call" fn`) is explicitly allowed to unwind
             // (unless it has no-unwind attribute, handled above).

src/librustc_codegen_llvm/callee.rs

@@ -80,7 +80,7 @@ pub fn get_fn(
         let llfn = cx.declare_fn(&sym, &fn_abi);
         debug!("get_fn: not casting pointer!");
 
-        attributes::from_fn_attrs(cx, llfn, instance);
+        attributes::from_fn_attrs(cx, llfn, instance, &fn_abi);
 
         let instance_def_id = instance.def_id();
 

src/librustc_codegen_llvm/mono_item.rs

@@ -70,7 +70,7 @@ impl PreDefineMethods<'tcx> for CodegenCx<'ll, 'tcx> {
 
         debug!("predefine_fn: instance = {:?}", instance);
 
-        attributes::from_fn_attrs(self, lldecl, instance);
+        attributes::from_fn_attrs(self, lldecl, instance, &fn_abi);
 
         self.instances.borrow_mut().insert(instance, lldecl);
     }

src/librustc_target/abi/call/mod.rs

@@ -492,7 +492,12 @@ impl<'a, Ty> ArgAbi<'a, Ty> {
 
 #[derive(Copy, Clone, PartialEq, Debug)]
 pub enum Conv {
+    // General language calling conventions, for which every target
+    // should have its own backend (e.g. LLVM) support.
     C,
+    Rust,
+
+    // Target-specific calling conventions.
 
     ArmAapcs,