Auto merge of #67502 - Mark-Simulacrum:opt-catch, r=<try>

Optimize catch_unwind to match C++ try/catch

This refactors the implementation of catching unwinds to allow LLVM to inline the "try" closure directly into the happy path, avoiding indirection. This means that the catch_unwind implementation is (after this PR) zero-cost unless a panic is thrown.

https://rust.godbolt.org/z/cZcUSB is an example of the current codegen in a simple case. Notably, the codegen is *exactly the same* if `-Cpanic=abort` is passed, which is clearly not great.

This PR, on the other hand, generates the following assembly:

```asm
# -Cpanic=unwind:
	push   rbx
	mov    ebx,0x2a
	call   QWORD PTR [rip+0x1c53c]        # <happy>
	mov    eax,ebx
	pop    rbx
	ret
	mov    rdi,rax
	call   QWORD PTR [rip+0x1c537]        # cleanup function call
	call   QWORD PTR [rip+0x1c539]        # <unfortunate>
	mov    ebx,0xd
	mov    eax,ebx
	pop    rbx
	ret

# -Cpanic=abort:
	push   rax
	call   QWORD PTR [rip+0x20a1]        # <happy>
	mov    eax,0x2a
	pop    rcx
	ret
```

Fixes #64224, and resolves #64222.

Author: bors

Cargo.lock

@@ -2290,6 +2290,7 @@ dependencies = [
 name = "panic_abort"
 version = "0.0.0"
 dependencies = [
+ "cfg-if",
  "compiler_builtins",
  "core",
  "libc",

src/ci/azure-pipelines/pr.yml

@@ -22,3 +22,54 @@ jobs:
       mingw-check: {}
       x86_64-gnu-tools:
         CI_ONLY_WHEN_SUBMODULES_CHANGED: 1
+- job: Windows
+  timeoutInMinutes: 600
+  pool:
+    vmImage: 'vs2017-win2016'
+  steps:
+  - template: steps/run.yml
+  strategy:
+    matrix:
+      x86_64-msvc-1:
+        RUST_CONFIGURE_ARGS: --build=x86_64-pc-windows-msvc --enable-profiler
+        SCRIPT: make ci-subset-1
+        # FIXME(#59637)
+        NO_DEBUG_ASSERTIONS: 1
+        NO_LLVM_ASSERTIONS: 1
+      x86_64-msvc-2:
+        RUST_CONFIGURE_ARGS: --build=x86_64-pc-windows-msvc --enable-profiler
+        SCRIPT: make ci-subset-2
+      i686-msvc-1:
+        RUST_CONFIGURE_ARGS: --build=i686-pc-windows-msvc
+        SCRIPT: make ci-subset-1
+        # FIXME(#59637)
+        NO_DEBUG_ASSERTIONS: 1
+        NO_LLVM_ASSERTIONS: 1
+      i686-msvc-2:
+        RUST_CONFIGURE_ARGS: --build=i686-pc-windows-msvc
+        SCRIPT: make ci-subset-2
+        # FIXME(#59637)
+        NO_DEBUG_ASSERTIONS: 1
+        NO_LLVM_ASSERTIONS: 1
+      i686-mingw-1:
+        RUST_CONFIGURE_ARGS: --build=i686-pc-windows-gnu
+        SCRIPT: make ci-mingw-subset-1
+        CUSTOM_MINGW: 1
+        # FIXME(#59637)
+        NO_DEBUG_ASSERTIONS: 1
+        NO_LLVM_ASSERTIONS: 1
+      i686-mingw-2:
+        RUST_CONFIGURE_ARGS: --build=i686-pc-windows-gnu
+        SCRIPT: make ci-mingw-subset-2
+        CUSTOM_MINGW: 1
+      x86_64-mingw-1:
+        SCRIPT: make ci-mingw-subset-1
+        RUST_CONFIGURE_ARGS: --build=x86_64-pc-windows-gnu
+        CUSTOM_MINGW: 1
+        # FIXME(#59637)
+        NO_DEBUG_ASSERTIONS: 1
+        NO_LLVM_ASSERTIONS: 1
+      x86_64-mingw-2:
+        SCRIPT: make ci-mingw-subset-2
+        RUST_CONFIGURE_ARGS: --build=x86_64-pc-windows-gnu
+        CUSTOM_MINGW: 1

src/ci/azure-pipelines/try.yml

@@ -6,17 +6,17 @@ variables:
 - group: prod-credentials
 
 jobs:
-- job: Linux
-  timeoutInMinutes: 600
-  pool:
-    vmImage: ubuntu-16.04
-  steps:
-  - template: steps/run.yml
-  strategy:
-    matrix:
-      dist-x86_64-linux: {}
-      dist-x86_64-linux-alt:
-        IMAGE: dist-x86_64-linux
+    # - job: Linux
+    #   timeoutInMinutes: 600
+    #   pool:
+    #     vmImage: ubuntu-16.04
+    #   steps:
+    #   - template: steps/run.yml
+    #   strategy:
+    #     matrix:
+    #       dist-x86_64-linux: {}
+    #       dist-x86_64-linux-alt:
+    #         IMAGE: dist-x86_64-linux
 
 # The macOS and Windows builds here are currently disabled due to them not being
 # overly necessary on `try` builds. We also don't actually have anything that
@@ -49,25 +49,20 @@ jobs:
 #         NO_LLVM_ASSERTIONS: 1
 #         NO_DEBUG_ASSERTIONS: 1
 #
-# - job: Windows
-#   timeoutInMinutes: 600
-#   pool:
-#     vmImage: 'vs2017-win2016'
-#   steps:
-#   - template: steps/run.yml
-#   strategy:
-#     matrix:
-#       dist-x86_64-msvc:
-#         RUST_CONFIGURE_ARGS: >
-#           --build=x86_64-pc-windows-msvc
-#           --target=x86_64-pc-windows-msvc,aarch64-pc-windows-msvc
-#           --enable-full-tools
-#           --enable-profiler
-#         SCRIPT: python x.py dist
-#         DIST_REQUIRE_ALL_TOOLS: 1
-#         DEPLOY: 1
-#
-#       dist-x86_64-msvc-alt:
-#         RUST_CONFIGURE_ARGS: --build=x86_64-pc-windows-msvc --enable-extended --enable-profiler
-#         SCRIPT: python x.py dist
-#         DEPLOY_ALT: 1
+- job: Windows
+  timeoutInMinutes: 600
+  pool:
+    vmImage: 'vs2017-win2016'
+  steps:
+  - template: steps/run.yml
+  strategy:
+    matrix:
+      i686-mingw-2:
+        RUST_CONFIGURE_ARGS: --build=i686-pc-windows-gnu
+        SCRIPT: make ci-mingw-subset-2
+        CUSTOM_MINGW: 1
+      dist-i686-mingw:
+        RUST_CONFIGURE_ARGS: --build=i686-pc-windows-gnu --enable-debug-assertions --enable-optimize --debuginfo-level=1
+        SCRIPT: python x.py dist
+        CUSTOM_MINGW: 1
+        N_DIST_REQUIRE_ALL_TOOLS: 1

src/doc/unstable-book/src/language-features/lang-items.md

@@ -52,7 +52,6 @@ fn main(_argc: isize, _argv: *const *const u8) -> isize {
 
 #[lang = "eh_personality"] extern fn rust_eh_personality() {}
 #[lang = "panic_impl"] extern fn rust_begin_panic(info: &PanicInfo) -> ! { unsafe { intrinsics::abort() } }
-#[lang = "eh_unwind_resume"] extern fn rust_eh_unwind_resume() {}
 #[no_mangle] pub extern fn rust_eh_register_frames () {}
 #[no_mangle] pub extern fn rust_eh_unregister_frames () {}
 ```
@@ -67,7 +66,7 @@ Other features provided by lang items include:
   marked with lang items; those specific four are `eq`, `ord`,
   `deref`, and `add` respectively.
 - stack unwinding and general failure; the `eh_personality`,
-  `eh_unwind_resume`, `fail` and `fail_bounds_checks` lang items.
+  `fail` and `fail_bounds_checks` lang items.
 - the traits in `std::marker` used to indicate types of
   various kinds; lang items `send`, `sync` and `copy`.
 - the marker types and variance indicators found in
@@ -130,12 +129,6 @@ fn start(_argc: isize, _argv: *const *const u8) -> isize {
 pub extern fn rust_eh_personality() {
 }
 
-// This function may be needed based on the compilation target.
-#[lang = "eh_unwind_resume"]
-#[no_mangle]
-pub extern fn rust_eh_unwind_resume() {
-}
-
 #[lang = "panic_impl"]
 #[no_mangle]
 pub extern fn rust_begin_panic(info: &PanicInfo) -> ! {
@@ -173,12 +166,6 @@ pub extern fn main(_argc: i32, _argv: *const *const u8) -> i32 {
 pub extern fn rust_eh_personality() {
 }
 
-// This function may be needed based on the compilation target.
-#[lang = "eh_unwind_resume"]
-#[no_mangle]
-pub extern fn rust_eh_unwind_resume() {
-}
-
 #[lang = "panic_impl"]
 #[no_mangle]
 pub extern fn rust_begin_panic(info: &PanicInfo) -> ! {
@@ -213,8 +200,8 @@ the screen. While the language item's name is `panic_impl`, the symbol name is
 
 A third function, `rust_eh_unwind_resume`, is also needed if the `custom_unwind_resume`
 flag is set in the options of the compilation target. It allows customizing the
-process of resuming unwind at the end of the landing pads. The language item's name
-is `eh_unwind_resume`.
+process of resuming unwind at the end of the landing pads. Since this function
+must be defined in assembly code it does not have an associated language item.
 
 ## List of all language items
 
@@ -247,9 +234,8 @@ the source code.
   - `eh_personality`: `libpanic_unwind/emcc.rs` (EMCC)
   - `eh_personality`: `libpanic_unwind/gcc.rs` (GNU)
   - `eh_personality`: `libpanic_unwind/seh.rs` (SEH)
-  - `eh_unwind_resume`: `libpanic_unwind/gcc.rs` (GCC)
-  - `eh_catch_typeinfo`: `libpanic_unwind/seh.rs` (SEH)
   - `eh_catch_typeinfo`: `libpanic_unwind/emcc.rs` (EMCC)
+  - `rust_eh_unwind_resume`: `libpanic_unwind/gcc.rs` (GCC)
   - `panic`: `libcore/panicking.rs`
   - `panic_bounds_check`: `libcore/panicking.rs`
   - `panic_impl`: `libcore/panicking.rs`

src/libcore/intrinsics.rs

@@ -1854,14 +1854,16 @@ extern "rust-intrinsic" {
     /// [`std::mem::discriminant`](../../std/mem/fn.discriminant.html)
     pub fn discriminant_value<T>(v: &T) -> u64;
 
-    /// Rust's "try catch" construct which invokes the function pointer `f` with
-    /// the data pointer `data`.
+    /// Rust's "try catch" construct which invokes the function pointer `try_fn`
+    /// with the data pointer `data`.
     ///
-    /// The third pointer is a target-specific data pointer which is filled in
-    /// with the specifics of the exception that occurred. For examples on Unix
-    /// platforms this is a `*mut *mut T` which is filled in by the compiler and
-    /// on MSVC it's `*mut [usize; 2]`. For more information see the compiler's
+    /// The third argument is a function called if a panic occurs. This function
+    /// takes the data pointer and a pointer to the target-specific exception
+    /// object that was caught. For more information see the compiler's
     /// source as well as std's catch implementation.
+    #[cfg(not(bootstrap))]
+    pub fn r#try(try_fn: fn(*mut u8), data: *mut u8, catch_fn: fn(*mut u8, *mut u8)) -> i32;
+    #[cfg(bootstrap)]
     pub fn r#try(f: fn(*mut u8), data: *mut u8, local_ptr: *mut u8) -> i32;
 
     /// Emits a `!nontemporal` store according to LLVM (see their docs).

src/libpanic_abort/Cargo.toml

@@ -14,3 +14,4 @@ doc = false
 core = { path = "../libcore" }
 libc = { version = "0.2", default-features = false }
 compiler_builtins = "0.1.0"
+cfg-if = "0.1.8"

src/libpanic_abort/lib.rs

@@ -18,17 +18,11 @@
 #![feature(staged_api)]
 #![feature(rustc_attrs)]
 
-// Rust's "try" function, but if we're aborting on panics we just call the
-// function as there's nothing else we need to do here.
+use core::any::Any;
+
 #[rustc_std_internal_symbol]
-pub unsafe extern "C" fn __rust_maybe_catch_panic(
-    f: fn(*mut u8),
-    data: *mut u8,
-    _data_ptr: *mut usize,
-    _vtable_ptr: *mut usize,
-) -> u32 {
-    f(data);
-    0
+pub unsafe extern "C" fn __rust_panic_cleanup(_: *mut u8) -> *mut (dyn Any + Send + 'static) {
+    unreachable!()
 }
 
 // "Leak" the payload and shim to the relevant abort on the platform in
@@ -92,7 +86,7 @@ pub unsafe extern "C" fn __rust_start_panic(_payload: usize) -> u32 {
 // binaries, but it should never be called as we don't link in an unwinding
 // runtime at all.
 pub mod personalities {
-    #[no_mangle]
+    #[rustc_std_internal_symbol]
     #[cfg(not(any(
         all(target_arch = "wasm32", not(target_os = "emscripten"),),
         all(target_os = "windows", target_env = "gnu", target_arch = "x86_64",),
@@ -101,7 +95,7 @@ pub mod personalities {
 
     // On x86_64-pc-windows-gnu we use our own personality function that needs
     // to return `ExceptionContinueSearch` as we're passing on all our frames.
-    #[no_mangle]
+    #[rustc_std_internal_symbol]
     #[cfg(all(target_os = "windows", target_env = "gnu", target_arch = "x86_64"))]
     pub extern "C" fn rust_eh_personality(
         _record: usize,
@@ -117,16 +111,16 @@ pub mod personalities {
     //
     // Note that we don't execute landing pads, so this is never called, so it's
     // body is empty.
-    #[no_mangle]
+    #[rustc_std_internal_symbol]
     #[cfg(all(target_os = "windows", target_env = "gnu"))]
     pub extern "C" fn rust_eh_unwind_resume() {}
 
     // These two are called by our startup objects on i686-pc-windows-gnu, but
     // they don't need to do anything so the bodies are nops.
-    #[no_mangle]
+    #[rustc_std_internal_symbol]
     #[cfg(all(target_os = "windows", target_env = "gnu", target_arch = "x86"))]
     pub extern "C" fn rust_eh_register_frames() {}
-    #[no_mangle]
+    #[rustc_std_internal_symbol]
     #[cfg(all(target_os = "windows", target_env = "gnu", target_arch = "x86"))]
     pub extern "C" fn rust_eh_unregister_frames() {}
 }

src/libpanic_unwind/dummy.rs

@@ -6,10 +6,6 @@ use alloc::boxed::Box;
 use core::any::Any;
 use core::intrinsics;
 
-pub fn payload() -> *mut u8 {
-    core::ptr::null_mut()
-}
-
 pub unsafe fn cleanup(_ptr: *mut u8) -> Box<dyn Any + Send> {
     intrinsics::abort()
 }

src/libpanic_unwind/emcc.rs

@@ -48,15 +48,11 @@ static EXCEPTION_TYPE_INFO: TypeInfo = TypeInfo {
     name: b"rust_panic\0".as_ptr(),
 };
 
-pub fn payload() -> *mut u8 {
-    ptr::null_mut()
-}
-
 struct Exception {
     // This needs to be an Option because the object's lifetime follows C++
     // semantics: when catch_unwind moves the Box out of the exception it must
     // still leave the exception object in a valid state because its destructor
-    // is still going to be called by __cxa_end_catch..
+    // is still going to be called by __cxa_end_catch.
     data: Option<Box<dyn Any + Send>>,
 }
 
@@ -98,7 +94,6 @@ extern "C" fn exception_cleanup(ptr: *mut libc::c_void) -> DestructorRet {
 }
 
 #[lang = "eh_personality"]
-#[no_mangle]
 unsafe extern "C" fn rust_eh_personality(
     version: c_int,
     actions: uw::_Unwind_Action,