[clang] [llvm] [AArch64] Fix _sys implemantation and MRS/MSR Sema checks (PR #187290)

[via cfe-commits]

github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Windows-->
# :window: Windows x64 Test Results

* 132424 tests passed
* 3012 tests skipped
* 1 test failed

## Failed Tests
(click on a test name to see its output)

### Clang
<details>
<summary>Clang.CodeGen/arm64-microsoft-sys.c</summary>

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 3
c:\_work\llvm-project\llvm-project\build\bin\clang.exe -cc1 -internal-isystem C:\_work\llvm-project\llvm-project\build\lib\clang\23\include -nostdsysteminc -triple arm64-windows -fms-compatibility -S  -o - C:\_work\llvm-project\llvm-project\clang\test\CodeGen\arm64-microsoft-sys.c | c:\_work\llvm-project\llvm-project\build\bin\filecheck.exe C:\_work\llvm-project\llvm-project\clang\test\CodeGen\arm64-microsoft-sys.c -check-prefix CHECK-ASM
# executed command: 'c:\_work\llvm-project\llvm-project\build\bin\clang.exe' -cc1 -internal-isystem 'C:\_work\llvm-project\llvm-project\build\lib\clang\23\include' -nostdsysteminc -triple arm64-windows -fms-compatibility -S -o - 'C:\_work\llvm-project\llvm-project\clang\test\CodeGen\arm64-microsoft-sys.c'
# note: command had no output on stdout or stderr
# executed command: 'c:\_work\llvm-project\llvm-project\build\bin\filecheck.exe' 'C:\_work\llvm-project\llvm-project\clang\test\CodeGen\arm64-microsoft-sys.c' -check-prefix CHECK-ASM
# .---command stderr------------
# | C:\_work\llvm-project\llvm-project\clang\test\CodeGen\arm64-microsoft-sys.c:36:15: error: CHECK-ASM: expected string not found in input
# | // CHECK-ASM: msr S1_0_C7_C10_6, x8
# |               ^
# | <stdin>:1:1: note: scanning from here
# |  .def "@feat.00";
# | ^
# | <stdin>:20:10: note: possible intended match here
# |  sys #0, c7, c10, #6, x8
# |          ^
# | 
# | Input file: <stdin>
# | Check file: C:\_work\llvm-project\llvm-project\clang\test\CodeGen\arm64-microsoft-sys.c
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |             1:  .def "@feat.00"; 
# | check:36'0     X~~~~~~~~~~~~~~~~~ error: no match found
# |             2:  .scl 3; 
# | check:36'0     ~~~~~~~~~
# |             3:  .type 0; 
# | check:36'0     ~~~~~~~~~~
# |             4:  .endef 
# | check:36'0     ~~~~~~~~
# |             5:  .globl "@feat.00" 
# | check:36'0     ~~~~~~~~~~~~~~~~~~~
# |             6: "@feat.00" = 0 
# | check:36'0     ~~~~~~~~~~~~~~~
# |             .
# |             .
# |             .
# |            15: check__sys: // @check__sys 
# | check:36'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |            16: // %bb.0: // %entry 
# | check:36'0     ~~~~~~~~~~~~~~~~~~~~
# |            17:  sub sp, sp, #16 
# | check:36'0     ~~~~~~~~~~~~~~~~~
# |            18:  str x0, [sp, #8] 
# | check:36'0     ~~~~~~~~~~~~~~~~~~
# |            19:  ldr x8, [sp, #8] 
# | check:36'0     ~~~~~~~~~~~~~~~~~~
# |            20:  sys #0, c7, c10, #6, x8 
# | check:36'0     ~~~~~~~~~~~~~~~~~~~~~~~~~
# | check:36'1              ?                possible intended match
# |            21:  ldr x8, [sp, #8] 
# | check:36'0     ~~~~~~~~~~~~~~~~~~
# |            22:  sys #0, c7, c5, #0, x8 
# | check:36'0     ~~~~~~~~~~~~~~~~~~~~~~~~
# |            23:  ldr x8, [sp, #8] 
# | check:36'0     ~~~~~~~~~~~~~~~~~~
# |            24:  at s1e2w, x8 
# | check:36'0     ~~~~~~~~~~~~~~
# |            25:  ldr x8, [sp, #8] 
# | check:36'0     ~~~~~~~~~~~~~~~~~~
# |             .
# |             .
# |             .
# | >>>>>>
# `-----------------------------
# error: command failed with exit status: 1

--

```
</details>

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the `infrastructure` label.

https://github.com/llvm/llvm-project/pull/187290