[llvm] [ARM][Thumb2] Mark BTI-clearing instructions as scheduling region boundaries (PR #79173)

[Anatoly Trosinenko via llvm-commits]

================
@@ -0,0 +1,181 @@
+# RUN: llc -o - -run-pass=machine-scheduler -misched=shuffle %s | FileCheck %s
+# RUN: llc -o - -run-pass=postmisched %s | FileCheck %s
+
+--- |
+  target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
----------------
atrosinenko wrote:

The inline LLVM IR module can probably be simplified by dropping non-essential attributes, as suggested in [TestingGuide](https://llvm.org/docs/TestingGuide.html). [MIR-specific](https://llvm.org/docs/MIRLangRef.html#simplifying-mir-files) documentation also suggests that lots of autogenerated YAML attributes are likely to be safe to remove, but many are dropped already in this test.

I guess the machine functions themselves can be made simpler by dropping `CFI_INSTRUCTION`s and so on, but I'm not sure.

https://github.com/llvm/llvm-project/pull/79173