Sync x86 chkstk intrinsics with LLVM

Incorporates the following commits:
llvm/llvm-project@885d7b7
llvm/llvm-project@1f9eff1
llvm/llvm-project@7a5cba8

Author: kleisauke

README.md

@@ -163,7 +163,6 @@ features = ["c"]
 - [ ] i386/ashldi3.S
 - [ ] i386/ashrdi3.S
 - [x] i386/chkstk.S
-- [x] i386/chkstk2.S
 - [ ] i386/divdi3.S
 - [ ] i386/lshrdi3.S
 - [ ] i386/moddi3.S
@@ -192,7 +191,6 @@ features = ["c"]
 - [x] umoddi3.c
 - [x] umodsi3.c
 - [x] x86_64/chkstk.S
-- [x] x86_64/chkstk2.S
 
 These builtins are needed to support 128-bit integers, which are in the process of being added to Rust.
 

src/x86.rs

@@ -6,7 +6,6 @@ use core::intrinsics;
 // calling convention which can't be implemented using a normal Rust function
 
 // NOTE These functions are never mangled as they are not tested against compiler-rt
-// and mangling ___chkstk would break the `jmp ___chkstk` instruction in __alloca
 
 intrinsics! {
     #[naked]
@@ -15,50 +14,8 @@ intrinsics! {
         target_env = "gnu",
         not(feature = "no-asm")
     ))]
-    pub unsafe extern "C" fn ___chkstk_ms() {
-        core::arch::asm!(
-            "push   %ecx",
-            "push   %eax",
-            "cmp    $0x1000,%eax",
-            "lea    12(%esp),%ecx",
-            "jb     1f",
-            "2:",
-            "sub    $0x1000,%ecx",
-            "test   %ecx,(%ecx)",
-            "sub    $0x1000,%eax",
-            "cmp    $0x1000,%eax",
-            "ja     2b",
-            "1:",
-            "sub    %eax,%ecx",
-            "test   %ecx,(%ecx)",
-            "pop    %eax",
-            "pop    %ecx",
-            "ret",
-            options(noreturn, att_syntax)
-        );
-    }
-
-    // FIXME: __alloca should be an alias to __chkstk
-    #[naked]
-    #[cfg(all(
-        windows,
-        target_env = "gnu",
-        not(feature = "no-asm")
-    ))]
-    pub unsafe extern "C" fn __alloca() {
-        core::arch::asm!(
-            "jmp ___chkstk", // Jump to ___chkstk since fallthrough may be unreliable"
-            options(noreturn, att_syntax)
-        );
-    }
-
-    #[naked]
-    #[cfg(all(
-        windows,
-        target_env = "gnu",
-        not(feature = "no-asm")
-    ))]
-    pub unsafe extern "C" fn ___chkstk() {
+    pub unsafe extern "C" fn _alloca() {
+        // _chkstk and _alloca are the same function
         core::arch::asm!(
             "push   %ecx",
             "cmp    $0x1000,%eax",

src/x86_64.rs

@@ -6,7 +6,6 @@ use core::intrinsics;
 // calling convention which can't be implemented using a normal Rust function
 
 // NOTE These functions are never mangled as they are not tested against compiler-rt
-// and mangling ___chkstk would break the `jmp ___chkstk` instruction in __alloca
 
 intrinsics! {
     #[naked]
@@ -36,49 +35,6 @@ intrinsics! {
             options(noreturn, att_syntax)
         );
     }
-
-    #[naked]
-    #[cfg(all(
-        any(all(windows, target_env = "gnu"), target_os = "uefi"),
-        not(feature = "no-asm")
-    ))]
-    pub unsafe extern "C" fn __alloca() {
-        core::arch::asm!(
-            "mov    %rcx,%rax", // x64 _alloca is a normal function with parameter in rcx
-            "jmp    ___chkstk", // Jump to ___chkstk since fallthrough may be unreliable"
-            options(noreturn, att_syntax)
-        );
-    }
-
-    #[naked]
-    #[cfg(all(
-        any(all(windows, target_env = "gnu"), target_os = "uefi"),
-        not(feature = "no-asm")
-    ))]
-    pub unsafe extern "C" fn ___chkstk() {
-        core::arch::asm!(
-            "push   %rcx",
-            "cmp    $0x1000,%rax",
-            "lea    16(%rsp),%rcx", // rsp before calling this routine -> rcx
-            "jb     1f",
-            "2:",
-            "sub    $0x1000,%rcx",
-            "test   %rcx,(%rcx)",
-            "sub    $0x1000,%rax",
-            "cmp    $0x1000,%rax",
-            "ja     2b",
-            "1:",
-            "sub    %rax,%rcx",
-            "test   %rcx,(%rcx)",
-            "lea    8(%rsp),%rax",  // load pointer to the return address into rax
-            "mov    %rcx,%rsp",     // install the new top of stack pointer into rsp
-            "mov    -8(%rax),%rcx", // restore rcx
-            "push   (%rax)",        // push return address onto the stack
-            "sub    %rsp,%rax",     // restore the original value in rax
-            "ret",
-            options(noreturn, att_syntax)
-        );
-    }
 }
 
 // HACK(https://github.com/rust-lang/rust/issues/62785): x86_64-unknown-uefi needs special LLVM