[llvm] [CFIFixup] Factor logic into helpers and use range-based loops (NFC) (PR #125137)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `openmp-s390x-linux` running on `systemz-1` while building `llvm` at step 5 "compile-openmp".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/88/builds/7482

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

```
Step 5 (compile-openmp) failure: build (failure)
...
13.628 [4523/4/752] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/AIXException.cpp.o
13.655 [4522/4/753] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/AsmPrinterDwarf.cpp.o
13.695 [4521/4/754] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/DbgEntityHistoryCalculator.cpp.o
13.704 [4520/4/755] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/AsmPrinterInlineAsm.cpp.o
13.728 [4519/4/756] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/DebugHandlerBase.cpp.o
13.744 [4518/4/757] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/DebugLocStream.cpp.o
13.764 [4517/4/758] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/DIE.cpp.o
13.801 [4516/4/759] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/DwarfCFIException.cpp.o
13.825 [4515/4/760] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/DIEHash.cpp.o
13.847 [4514/4/761] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o
FAILED: lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o 
CCACHE_CPP2=yes CCACHE_HASHDIR=yes /usr/bin/ccache /usr/bin/c++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/lib/CodeGen -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/llvm/lib/CodeGen -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/include -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -fno-lifetime-dse -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -std=c++17 -MD -MT lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o -MF lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o.d -o lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/CFIFixup.cpp.o -c /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/llvm/lib/CodeGen/CFIFixup.cpp
/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/llvm/lib/CodeGen/CFIFixup.cpp: In function 'llvm::SmallVector<BlockFlags> computeBlockInfo(const llvm::MachineFunction&, const llvm::MachineBasicBlock*)':
/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/llvm/lib/CodeGen/CFIFixup.cpp:174:10: error: could not convert 'BlockInfo' from 'SmallVector<[...],32>' to 'SmallVector<[...],40>'
  174 |   return BlockInfo;
      |          ^~~~~~~~~
      |          |
      |          SmallVector<[...],32>
13.869 [4514/3/762] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/DwarfCompileUnit.cpp.o
13.903 [4514/2/763] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/DwarfDebug.cpp.o
28.257 [4514/1/764] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/AsmPrinter.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/125137