Rollup merge of rust-lang#67502 - Mark-Simulacrum:opt-catch, r=alexcrichton

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 rust-lang#64224, and resolves rust-lang#64222.

Author: Centril

Cargo.lock

@@ -2301,6 +2301,7 @@ dependencies = [
 name = "panic_abort"
 version = "0.0.0"
 dependencies = [
+ "cfg-if",
  "compiler_builtins",
  "core",
  "libc",

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 +18,14 @@
 #![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;
+
+// We need the definition of TryPayload for __rust_panic_cleanup.
+include!("../libpanic_unwind/payload.rs");
+
 #[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(_: TryPayload) -> *mut (dyn Any + Send + 'static) {
+    unreachable!()
 }
 
 // "Leak" the payload and shim to the relevant abort on the platform in

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

@@ -48,10 +48,6 @@ static EXCEPTION_TYPE_INFO: TypeInfo = TypeInfo {
     name: b"rust_panic\0".as_ptr(),
 };
 
-pub fn payload() -> *mut u8 {
-    ptr::null_mut()
-}
-
 pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
     assert!(!ptr.is_null());
     let adjusted_ptr = __cxa_begin_catch(ptr as *mut libc::c_void);

src/libpanic_unwind/gcc.rs

@@ -48,7 +48,6 @@
 
 use alloc::boxed::Box;
 use core::any::Any;
-use core::ptr;
 
 use crate::dwarf::eh::{self, EHAction, EHContext};
 use libc::{c_int, uintptr_t};
@@ -82,10 +81,6 @@ pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
     }
 }
 
-pub fn payload() -> *mut u8 {
-    ptr::null_mut()
-}
-
 pub unsafe fn cleanup(ptr: *mut u8) -> Box<dyn Any + Send> {
     let my_ep = ptr as *mut Exception;
     let cause = (*my_ep).cause.take();

src/libpanic_unwind/hermit.rs

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

src/libpanic_unwind/lib.rs

@@ -22,19 +22,20 @@
 #![feature(libc)]
 #![feature(nll)]
 #![feature(panic_unwind)]
-#![feature(raw)]
 #![feature(staged_api)]
 #![feature(std_internals)]
 #![feature(unwind_attributes)]
+#![feature(rustc_attrs)]
+#![feature(raw)]
 #![panic_runtime]
 #![feature(panic_runtime)]
 
 use alloc::boxed::Box;
-use core::intrinsics;
-use core::mem;
+use core::any::Any;
 use core::panic::BoxMeUp;
-use core::raw;
 
+// If adding to this list, you should also look at the list of TryPayload types
+// defined in payload.rs and likely add to there as well.
 cfg_if::cfg_if! {
     if #[cfg(target_os = "emscripten")] {
         #[path = "emcc.rs"]
@@ -60,30 +61,15 @@ cfg_if::cfg_if! {
     }
 }
 
+include!("payload.rs");
+
 mod dwarf;
 
-// Entry point for catching an exception, implemented using the `try` intrinsic
-// in the compiler.
-//
-// The interaction between the `payload` function and the compiler is pretty
-// hairy and tightly coupled, for more information see the compiler's
-// implementation of this.
 #[no_mangle]
-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 {
-    let mut payload = imp::payload();
-    if intrinsics::r#try(f, data, &mut payload as *mut _ as *mut _) == 0 {
-        0
-    } else {
-        let obj = mem::transmute::<_, raw::TraitObject>(imp::cleanup(payload));
-        *data_ptr = obj.data as usize;
-        *vtable_ptr = obj.vtable as usize;
-        1
-    }
+pub unsafe extern "C" fn __rust_panic_cleanup(
+    payload: TryPayload,
+) -> *mut (dyn Any + Send + 'static) {
+    Box::into_raw(imp::cleanup(payload))
 }
 
 // Entry point for raising an exception, just delegates to the platform-specific

src/libpanic_unwind/payload.rs

@@ -0,0 +1,21 @@
+// Type definition for the payload argument of the try intrinsic.
+//
+// This must be kept in sync with the implementations of the try intrinsic.
+//
+// This file is included by both panic runtimes and libstd. It is part of the
+// panic runtime ABI.
+cfg_if::cfg_if! {
+    if #[cfg(target_os = "emscripten")] {
+        type TryPayload = *mut u8;
+    } else if #[cfg(target_arch = "wasm32")] {
+        type TryPayload = *mut u8;
+    } else if #[cfg(target_os = "hermit")] {
+        type TryPayload = *mut u8;
+    } else if #[cfg(all(target_env = "msvc", target_arch = "aarch64"))] {
+        type TryPayload = *mut u8;
+    } else if #[cfg(target_env = "msvc")] {
+        type TryPayload = [u64; 2];
+    } else {
+        type TryPayload = *mut u8;
+    }
+}

src/libpanic_unwind/seh.rs

@@ -264,10 +264,6 @@ pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
     _CxxThrowException(throw_ptr, &mut THROW_INFO as *mut _ as *mut _);
 }
 
-pub fn payload() -> [u64; 2] {
-    [0; 2]
-}
-
 pub unsafe fn cleanup(payload: [u64; 2]) -> Box<dyn Any + Send> {
     mem::transmute(raw::TraitObject { data: payload[0] as *mut _, vtable: payload[1] as *mut _ })
 }