[llvm] [Analysis][NFC] Improve documentation for getMemoryOpCost (PR #156875)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-aarch64-darwin` running on `doug-worker-4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/190/builds/27142

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli -jit-kind=orc-lazy -compile-threads=2 -thread-entry hello /Users/buildbot/buildbot-root/llvm-project/llvm/test/ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll | /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/FileCheck /Users/buildbot/buildbot-root/llvm-project/llvm/test/ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll # RUN: at line 1
+ /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli -jit-kind=orc-lazy -compile-threads=2 -thread-entry hello /Users/buildbot/buildbot-root/llvm-project/llvm/test/ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll
+ /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/FileCheck /Users/buildbot/buildbot-root/llvm-project/llvm/test/ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and instructions to reproduce the bug.
Stack dump:
0.	Program arguments: /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli -jit-kind=orc-lazy -compile-threads=2 -thread-entry hello /Users/buildbot/buildbot-root/llvm-project/llvm/test/ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll
 #0 0x0000000103f01c0c llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli+0x100f09c0c)
 #1 0x0000000103eff9bc llvm::sys::RunSignalHandlers() (/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli+0x100f079bc)
 #2 0x0000000103f0270c SignalHandler(int, __siginfo*, void*) (/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli+0x100f0a70c)
 #3 0x000000019b7c7584 (/usr/lib/system/libsystem_platform.dylib+0x18047b584)
 #4 0x0000010103a5c098
 #5 0x0000000103a674e8 llvm::orc::ExecutionSession::removeJITDylibs(std::__1::vector<llvm::IntrusiveRefCntPtr<llvm::orc::JITDylib>, std::__1::allocator<llvm::IntrusiveRefCntPtr<llvm::orc::JITDylib>>>) (/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli+0x100a6f4e8)
 #6 0x0000000103a67298 llvm::orc::ExecutionSession::endSession() (/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli+0x100a6f298)
 #7 0x0000000103af2de8 llvm::orc::LLJIT::~LLJIT() (/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli+0x100afade8)
 #8 0x0000000103af7774 llvm::orc::LLLazyJIT::~LLLazyJIT() (/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli+0x100aff774)
 #9 0x0000000103002324 runOrcJIT(char const*) (/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli+0x10000a324)
#10 0x0000000102ffda54 main (/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/lli+0x100005a54)
#11 0x000000019b40b154
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/FileCheck /Users/buildbot/buildbot-root/llvm-project/llvm/test/ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/156875