Add support for x86-interrupt calling convention

Tracking issue: https://github.com/rust-lang/rust/issues/40180

This calling convention can be used for definining interrupt handlers on
32-bit and 64-bit x86 targets. The compiler then uses `iret` instead of
`ret` for returning and ensures that all registers are restored to their
original values.

Usage:

```
extern "x86-interrupt" fn handler(stack_frame: &ExceptionStackFrame) {…}
```

for interrupts and exceptions without error code and

```
extern "x86-interrupt" fn page_fault_handler(stack_frame: &ExceptionStackFrame,
                                             error_code: u64) {…}
```

for exceptions that push an error code (e.g., page faults or general
protection faults). The programmer must ensure that the correct version
is used for each interrupt.

For more details see the [LLVM PR][1] and the corresponding [proposal][2].

[1]: https://reviews.llvm.org/D15567
[2]: http://lists.llvm.org/pipermail/cfe-dev/2015-September/045171.html

src/librustc_llvm/ffi.rs

@@ -53,6 +53,7 @@ pub enum CallConv {
     X86_64_SysV = 78,
     X86_64_Win64 = 79,
     X86_VectorCall = 80,
+    X86_Intr = 83,
 }
 
 /// LLVMRustLinkage

src/librustc_trans/abi.rs

@@ -355,6 +355,7 @@ impl FnType {
             Aapcs => llvm::ArmAapcsCallConv,
             PtxKernel => llvm::PtxKernel,
             Msp430Interrupt => llvm::Msp430Intr,
+            X86Interrupt => llvm::X86_Intr,
 
             // These API constants ought to be more specific...
             Cdecl => llvm::CCallConv,

src/libsyntax/abi.rs

@@ -25,6 +25,7 @@ pub enum Abi {
     SysV64,
     PtxKernel,
     Msp430Interrupt,
+    X86Interrupt,
 
     // Multiplatform / generic ABIs
     Rust,
@@ -59,6 +60,7 @@ const AbiDatas: &'static [AbiData] = &[
     AbiData {abi: Abi::SysV64, name: "sysv64", generic: false },
     AbiData {abi: Abi::PtxKernel, name: "ptx-kernel", generic: false },
     AbiData {abi: Abi::Msp430Interrupt, name: "msp430-interrupt", generic: false },
+    AbiData {abi: Abi::X86Interrupt, name: "x86-interrupt", generic: false },
 
     // Cross-platform ABIs
     AbiData {abi: Abi::Rust, name: "Rust", generic: true },

src/libsyntax/feature_gate.rs

@@ -330,6 +330,9 @@ declare_features! (
     // Used to identify crates that contain sanitizer runtimes
     // rustc internal
     (active, sanitizer_runtime, "1.17.0", None),
+
+    // `extern "x86-interrupt" fn()`
+    (active, abi_x86_interrupt, "1.17.0", Some(40180)),
 );
 
 declare_features! (
@@ -1036,6 +1039,10 @@ impl<'a> PostExpansionVisitor<'a> {
                 gate_feature_post!(&self, abi_msp430_interrupt, span,
                                    "msp430-interrupt ABI is experimental and subject to change");
             },
+            Abi::X86Interrupt => {
+                gate_feature_post!(&self, abi_x86_interrupt, span,
+                                   "x86-interrupt ABI is experimental and subject to change");
+            },
             // Stable
             Abi::Cdecl |
             Abi::Stdcall |

src/test/codegen/abi-x86-interrupt.rs

@@ -0,0 +1,28 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Checks if the correct annotation for the x86-interrupt ABI is passed to
+// llvm. Also checks that the abi_x86_interrupt feature gate allows usage
+// of the x86-interrupt abi.
+
+// ignore-arm
+// ignore-aarch64
+// min-llvm-version 3.8
+
+// compile-flags: -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+#![feature(abi_x86_interrupt)]
+
+// CHECK: define x86_intrcc i64 @has_x86_interrupt_abi
+#[no_mangle]
+pub extern "x86-interrupt" fn has_x86_interrupt_abi(a: i64) -> i64 {
+    a * 2
+}

src/test/compile-fail/feature-gate-abi.rs

@@ -12,6 +12,7 @@
 // gate-test-platform_intrinsics
 // gate-test-abi_vectorcall
 // gate-test-abi_ptx
+// gate-test-abi_x86_interrupt
 
 // Functions
 extern "rust-intrinsic" fn f1() {} //~ ERROR intrinsics are subject to change
@@ -20,6 +21,7 @@ extern "vectorcall" fn f3() {} //~ ERROR vectorcall is experimental and subject
 extern "rust-call" fn f4() {} //~ ERROR rust-call ABI is subject to change
 extern "msp430-interrupt" fn f5() {} //~ ERROR msp430-interrupt ABI is experimental
 extern "ptx-kernel" fn f6() {} //~ ERROR PTX ABIs are experimental and subject to change
+extern "x86-interrupt" fn f7() {} //~ ERROR x86-interrupt ABI is experimental
 
 // Methods in trait definition
 trait Tr {
@@ -29,6 +31,7 @@ trait Tr {
     extern "rust-call" fn m4(); //~ ERROR rust-call ABI is subject to change
     extern "msp430-interrupt" fn m5(); //~ ERROR msp430-interrupt ABI is experimental
     extern "ptx-kernel" fn m6(); //~ ERROR PTX ABIs are experimental and subject to change
+    extern "x86-interrupt" fn m7(); //~ ERROR x86-interrupt ABI is experimental
 
     extern "rust-intrinsic" fn dm1() {} //~ ERROR intrinsics are subject to change
     extern "platform-intrinsic" fn dm2() {} //~ ERROR platform intrinsics are experimental
@@ -36,6 +39,7 @@ trait Tr {
     extern "rust-call" fn dm4() {} //~ ERROR rust-call ABI is subject to change
     extern "msp430-interrupt" fn dm5() {} //~ ERROR msp430-interrupt ABI is experimental
     extern "ptx-kernel" fn dm6() {} //~ ERROR PTX ABIs are experimental and subject to change
+    extern "x86-interrupt" fn dm7() {} //~ ERROR x86-interrupt ABI is experimental
 }
 
 struct S;
@@ -48,6 +52,7 @@ impl Tr for S {
     extern "rust-call" fn m4() {} //~ ERROR rust-call ABI is subject to change
     extern "msp430-interrupt" fn m5() {} //~ ERROR msp430-interrupt ABI is experimental
     extern "ptx-kernel" fn m6() {} //~ ERROR PTX ABIs are experimental and subject to change
+    extern "x86-interrupt" fn m7() {} //~ ERROR x86-interrupt ABI is experimental
 }
 
 // Methods in inherent impl
@@ -58,6 +63,7 @@ impl S {
     extern "rust-call" fn im4() {} //~ ERROR rust-call ABI is subject to change
     extern "msp430-interrupt" fn im5() {} //~ ERROR msp430-interrupt ABI is experimental
     extern "ptx-kernel" fn im6() {} //~ ERROR PTX ABIs are experimental and subject to change
+    extern "x86-interrupt" fn im7() {} //~ ERROR x86-interrupt ABI is experimental
 }
 
 // Function pointer types
@@ -67,6 +73,7 @@ type A3 = extern "vectorcall" fn(); //~ ERROR vectorcall is experimental and sub
 type A4 = extern "rust-call" fn(); //~ ERROR rust-call ABI is subject to change
 type A5 = extern "msp430-interrupt" fn(); //~ ERROR msp430-interrupt ABI is experimental
 type A6 = extern "ptx-kernel" fn (); //~ ERROR PTX ABIs are experimental and subject to change
+type A7 = extern "x86-interrupt" fn(); //~ ERROR x86-interrupt ABI is experimental
 
 // Foreign modules
 extern "rust-intrinsic" {} //~ ERROR intrinsics are subject to change
@@ -75,5 +82,6 @@ extern "vectorcall" {} //~ ERROR vectorcall is experimental and subject to chang
 extern "rust-call" {} //~ ERROR rust-call ABI is subject to change
 extern "msp430-interrupt" {} //~ ERROR msp430-interrupt ABI is experimental
 extern "ptx-kernel" {} //~ ERROR PTX ABIs are experimental and subject to change
+extern "x86-interrupt" {} //~ ERROR x86-interrupt ABI is experimental
 
 fn main() {}

src/test/ui/codemap_tests/unicode.stderr

@@ -1,4 +1,4 @@
-error: invalid ABI: expected one of [cdecl, stdcall, fastcall, vectorcall, aapcs, win64, sysv64, ptx-kernel, msp430-interrupt, Rust, C, system, rust-intrinsic, rust-call, platform-intrinsic, unadjusted], found `路濫狼á́́`
+error: invalid ABI: expected one of [cdecl, stdcall, fastcall, vectorcall, aapcs, win64, sysv64, ptx-kernel, msp430-interrupt, x86-interrupt, Rust, C, system, rust-intrinsic, rust-call, platform-intrinsic, unadjusted], found `路濫狼á́́`
   --> $DIR/unicode.rs:11:8
    |
 11 | extern "路濫狼á́́" fn foo() {}