do not validate the argument to the __breakpoint intrinsic

Author: gnzlbg

coresimd/arm/armclang.rs

@@ -2,24 +2,38 @@
 //!
 //! # References
 //!
-//! - [ARM Compiler v 6.10 - armclang Reference Guide](https://developer.arm.com/docs/100067/0610)
+//! - [ARM Compiler v 6.10 - armclang Reference Guide][arm_comp_ref]
+//!
+//! [arm_comp_ref]: https://developer.arm.com/docs/100067/0610
 
 #[cfg(test)]
 use stdsimd_test::assert_instr;
 
-/// This intrinsic inserts a BKPT instruction into the instruction stream generated by the compiler
+/// Inserts a breakpoint instruction.
+///
+/// `val` is a compile-time constant integer in range `[0, 255]`.
+///
+/// The breakpoint instruction inserted is:
+///
+/// * `BKPT` when compiling as T32,
+/// * `BRK` when compiling as A32 or A64.
 ///
-/// It enables you to include a breakpoint instruction in your Rust code
+/// # Safety
 ///
-/// `val` is a compile-time constant integer whose range is:
+/// If `val` is out-of-range the behavior is **undefined**.
 ///
-/// - `0...65535` if you are compiling source as A32 or A64 code.
-/// - `0...255` if you are compiling source as T32 code.
+/// # Note
 ///
-/// [ARM's documentation](https://developer.arm.com/docs/100067/latest/compiler-specific-intrinsics/__breakpoint-intrinsic)
+/// [ARM's documentation][arm_docs] defines that `__breakpoint` accepts the
+/// following values for `val`:
 ///
-/// **NOTE**: Due to compiler limitations this function only supports the range `0...255` in A32 and
-/// A64 mode.
+/// - `0...65535` when compiling as A32 or A64,
+/// - `0...255` when compiling as T32.
+///
+/// The current implementation only accepts values in range `[0, 255]` - if the
+/// value is out-of-range the behavior is **undefined**.
+///
+/// [arm_docs]: https://developer.arm.com/docs/100067/latest/compiler-specific-intrinsics/__breakpoint-intrinsic
 #[cfg_attr(all(test, target_arch = "arm"), assert_instr(bkpt, val = 0))]
 #[cfg_attr(all(test, target_arch = "aarch64"), assert_instr(brk, val = 0))]
 #[inline(always)]
@@ -39,8 +53,7 @@ pub unsafe fn __breakpoint(val: i32) {
         }
     }
 
-    // validate range
-    assert!(val >= 0 && val <= 255);
-
+    // We can't `panic!` inside this intrinsic, so we can't really validate the
+    // arguments here. If `val` is out-of-range this macro uses `val == 255`:
     constify_imm8!(val, call);
 }