[clang] Add check in SemaChecking for multiple unsequenced volatile accesses (PR #180955)

[via cfe-commits]

github-actions[bot] wrote:

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

* 56166 tests passed
* 1525 tests skipped
* 1 test failed

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

### Clang
<details>
<summary>Clang.CodeGen/SystemZ/builtins-systemz-zvector.c</summary>

```
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 2
c:\_work\llvm-project\llvm-project\build\bin\clang.exe -cc1 -internal-isystem C:\_work\llvm-project\llvm-project\build\lib\clang\24\include -nostdsysteminc -target-cpu z13 -triple s390x-linux-gnu  -O2 -fzvector -flax-vector-conversions=none  -Wall -Wno-unused -Werror -emit-llvm C:\_work\llvm-project\llvm-project\clang\test\CodeGen\SystemZ\builtins-systemz-zvector.c -o - | c:\_work\llvm-project\llvm-project\build\bin\filecheck.exe C:\_work\llvm-project\llvm-project\clang\test\CodeGen\SystemZ\builtins-systemz-zvector.c
# executed command: 'c:\_work\llvm-project\llvm-project\build\bin\clang.exe' -cc1 -internal-isystem 'C:\_work\llvm-project\llvm-project\build\lib\clang\24\include' -nostdsysteminc -target-cpu z13 -triple s390x-linux-gnu -O2 -fzvector -flax-vector-conversions=none -Wall -Wno-unused -Werror -emit-llvm 'C:\_work\llvm-project\llvm-project\clang\test\CodeGen\SystemZ\builtins-systemz-zvector.c' -o -
# .---command stderr------------
# | C:\_work\llvm-project\llvm-project\clang\test\CodeGen\SystemZ\builtins-systemz-zvector.c:772:31: error: unsequenced accesses to volatile qualified 'sl' [-Werror,-Wunsequenced]
# |   772 |   vsl = vec_load_pair(sl + 1, sl - 1);
# |       |                       ~~      ^
# | C:\_work\llvm-project\llvm-project\clang\test\CodeGen\SystemZ\builtins-systemz-zvector.c:774:31: error: unsequenced accesses to volatile qualified 'ul' [-Werror,-Wunsequenced]
# |   774 |   vul = vec_load_pair(ul + 1, ul - 1);
# |       |                       ~~      ^
# | 2 errors generated.
# `-----------------------------
# error: command failed with exit status: 1
# executed command: 'c:\_work\llvm-project\llvm-project\build\bin\filecheck.exe' 'C:\_work\llvm-project\llvm-project\clang\test\CodeGen\SystemZ\builtins-systemz-zvector.c'
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  c:\_work\llvm-project\llvm-project\build\bin\filecheck.exe C:\_work\llvm-project\llvm-project\clang\test\CodeGen\SystemZ\builtins-systemz-zvector.c
# `-----------------------------
# error: command failed with exit status: 2

--

```
</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/180955