[llvm] [SPARC] Weaken emitted barriers for atomic ops (PR #154950)

[Thurston Dang via llvm-commits]

thurstond wrote:

One of the buildbots is failing with CodeGen/SPARC/atomics-ordering.ll after this change (https://lab.llvm.org/buildbot/#/builders/24/builds/13433). Could you please take a look?

```
FAIL: LLVM :: CodeGen/SPARC/atomics-ordering.ll (44429 of 91124)
******************** TEST 'LLVM :: CodeGen/SPARC/atomics-ordering.ll' FAILED ********************
Exit Code: 2
Command Output (stdout):
--
# RUN: at line 2
/home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm_build_asan/bin/llc < /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm-project/llvm/test/CodeGen/SPARC/atomics-ordering.ll -mtriple=sparc -verify-machineinstrs | /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm_build_asan/bin/FileCheck /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm-project/llvm/test/CodeGen/SPARC/atomics-ordering.ll --check-prefixes=SPARC32
# executed command: /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm_build_asan/bin/llc -mtriple=sparc -verify-machineinstrs
# note: command had no output on stdout or stderr
# executed command: /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm_build_asan/bin/FileCheck /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm-project/llvm/test/CodeGen/SPARC/atomics-ordering.ll --check-prefixes=SPARC32
# note: command had no output on stdout or stderr
# RUN: at line 3
/home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm_build_asan/bin/llc < /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm-project/llvm/test/CodeGen/SPARC/atomics-ordering.ll -mtriple=sparc -mcpu=leon4 -verify-machineinstrs | /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm_build_asan/bin/FileCheck /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm-project/llvm/test/CodeGen/SPARC/atomics-ordering.ll --check-prefixes=SPARC32-LEON4
# executed command: /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm_build_asan/bin/llc -mtriple=sparc -mcpu=leon4 -verify-machineinstrs
# note: command had no output on stdout or stderr
# error: command failed with exit status: 1
# executed command: /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm_build_asan/bin/FileCheck /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm-project/llvm/test/CodeGen/SPARC/atomics-ordering.ll --check-prefixes=SPARC32-LEON4
# .---command stderr------------
# | FileCheck error: '<stdin>' is empty.
# | FileCheck command line:  /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm_build_asan/bin/FileCheck /home/b/sanitizer-aarch64-linux-bootstrap-asan/build/llvm-project/llvm/test/CodeGen/SPARC/atomics-ordering.ll --check-prefixes=SPARC32-LEON4
# `-----------------------------
# error: command failed with exit status: 2
--
```

https://github.com/llvm/llvm-project/pull/154950