[llvm] [CodeGen] Simplify code with *Map::operator[] (NFC) (PR #112075)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-darwin` running on `doug-worker-3` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/23/builds/3794

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
215.192 [121/12/5768] Linking CXX executable bin/llvm-cxxdump
215.337 [120/12/5769] Linking CXX executable bin/llvm-cxxmap
215.742 [119/12/5770] Linking CXX executable bin/llvm-debuginfod-find
215.804 [118/12/5771] Linking CXX executable bin/llvm-debuginfo-analyzer
215.889 [117/12/5772] Linking CXX executable bin/llvm-itanium-demangle-fuzzer
215.898 [116/12/5773] Linking CXX executable bin/llvm-debuginfod
216.058 [115/12/5774] Linking CXX executable bin/llvm-jitlink-executor
216.564 [114/12/5775] Linking CXX executable bin/llvm-dis
216.576 [113/12/5776] Linking CXX executable bin/llvm-diff
217.087 [112/12/5777] Linking CXX executable bin/llvm-lto2
FAILED: bin/llvm-lto2 
: && /usr/bin/clang++ -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -O3 -DNDEBUG -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX14.4.sdk -Wl,-search_paths_first -Wl,-headerpad_max_install_names -Wl,-dead_strip -Wl,-no_warn_duplicate_libraries -rdynamic tools/llvm-lto2/CMakeFiles/llvm-lto2.dir/llvm-lto2.cpp.o -o bin/llvm-lto2  -Wl,-rpath, at loader_path/../lib  lib/libLLVMX86AsmParser.a  lib/libLLVMX86CodeGen.a  lib/libLLVMX86Desc.a  lib/libLLVMX86Info.a  lib/libLLVMBitReader.a  lib/libLLVMCodeGen.a  lib/libLLVMCore.a  lib/libLLVMLinker.a  lib/libLLVMLTO.a  lib/libLLVMMC.a  lib/libLLVMObject.a  lib/libLLVMPasses.a  lib/libLLVMSupport.a  lib/libLLVMTarget.a  lib/libLLVMTargetParser.a  lib/libLLVMMCDisassembler.a  lib/libLLVMAsmPrinter.a  lib/libLLVMGlobalISel.a  lib/libLLVMSelectionDAG.a  lib/libLLVMCodeGen.a  lib/libLLVMCFGuard.a  lib/libLLVMIRPrinter.a  lib/libLLVMCoroutines.a  lib/libLLVMHipStdPar.a  lib/libLLVMTarget.a  lib/libLLVMCodeGenTypes.a  lib/libLLVMCGData.a  lib/libLLVMObjCARCOpts.a  lib/libLLVMExtensions.a  lib/libLLVMipo.a  lib/libLLVMLinker.a  lib/libLLVMInstrumentation.a  lib/libLLVMBitWriter.a  lib/libLLVMVectorize.a  lib/libLLVMSandboxIR.a  lib/libLLVMFrontendOpenMP.a  lib/libLLVMScalarOpts.a  lib/libLLVMAggressiveInstCombine.a  lib/libLLVMFrontendOffloading.a  lib/libLLVMInstCombine.a  lib/libLLVMTransformUtils.a  lib/libLLVMAnalysis.a  lib/libLLVMProfileData.a  lib/libLLVMSymbolize.a  lib/libLLVMDebugInfoDWARF.a  lib/libLLVMDebugInfoPDB.a  lib/libLLVMObject.a  lib/libLLVMMCParser.a  lib/libLLVMMC.a  lib/libLLVMIRReader.a  lib/libLLVMBitReader.a  lib/libLLVMAsmParser.a  lib/libLLVMCore.a  lib/libLLVMRemarks.a  lib/libLLVMBitstreamReader.a  lib/libLLVMTextAPI.a  lib/libLLVMDebugInfoCodeView.a  lib/libLLVMDebugInfoMSF.a  lib/libLLVMDebugInfoBTF.a  lib/libLLVMBinaryFormat.a  lib/libLLVMTargetParser.a  lib/libLLVMSupport.a  lib/libLLVMDemangle.a  -lm  /Library/Developer/CommandLineTools/SDKs/MacOSX14.4.sdk/usr/lib/libz.tbd  /usr/local/lib/libzstd.dylib && :
clang: error: unable to execute command: Abort trap: 6
clang: error: linker command failed due to signal (use -v to see invocation)
217.489 [112/11/5778] Linking CXX executable bin/llvm-ifs
217.837 [112/10/5779] Linking CXX executable bin/llvm-dwarfutil
218.032 [112/9/5780] Linking CXX executable bin/llvm-extract
218.089 [112/8/5781] Linking CXX executable bin/llvm-dwp
218.268 [112/7/5782] Linking CXX executable bin/llvm-exegesis
218.411 [112/6/5783] Linking CXX executable bin/llvm-isel-fuzzer
218.411 [112/5/5784] Linking CXX executable bin/llvm-libtool-darwin
218.472 [112/4/5785] Linking CXX executable bin/llvm-link
218.541 [112/3/5786] Linking CXX executable bin/llvm-gsymutil
218.551 [112/2/5787] Linking CXX executable bin/llvm-jitlink
218.558 [112/1/5788] Linking CXX executable bin/llvm-lipo
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/112075