[llvm] [AArch64][MachineCombiner] Reassociate long chains of accumulation instructions into a tree to increase ILP (PR #126060)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-armv8-quick` running on `linaro-clang-armv8-quick` while building `llvm` at step 4 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/154/builds/13816

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

```
Step 4 (build stage 1) failure: 'ninja' (failure)
...
[76/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/MachinePipeliner.cpp.o
[77/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TailDuplication.cpp.o
[78/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/RegAllocScore.cpp.o
[79/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/XRayInstrumentation.cpp.o
[80/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/ShrinkWrap.cpp.o
[81/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/VirtRegMap.cpp.o
[82/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/RegisterCoalescer.cpp.o
[83/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/RenameIndependentSubregs.cpp.o
[84/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TailDuplicator.cpp.o
[85/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o
FAILED: lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o 
/usr/local/bin/c++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_FILE_OFFSET_BITS=64 -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D_LARGEFILE_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/lib/CodeGen -I/home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/lib/CodeGen -I/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/include -I/home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/include -fPIC -fno-semantic-interposition -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 -ffunction-sections -fdata-sections -O3 -DNDEBUG -std=c++17  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -MD -MT lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o -MF lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o.d -o lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o -c /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/lib/CodeGen/TargetInstrInfo.cpp
../llvm/llvm/lib/CodeGen/TargetInstrInfo.cpp:1514:29: error: non-const lvalue reference to type 'DenseMap<unsigned int, [...]>' cannot bind to a value of unrelated type 'DenseMap<Register, [...]>'
 1514 |                             InstIdxForVirtReg, Root.getOperand(0).getReg());
      |                             ^~~~~~~~~~~~~~~~~
../llvm/llvm/lib/CodeGen/TargetInstrInfo.cpp:1021:35: note: passing argument to parameter 'InstrIdxForVirtReg' here
 1021 |     DenseMap<unsigned, unsigned> &InstrIdxForVirtReg,
      |                                   ^
1 error generated.
[86/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/VLIWMachineScheduler.cpp.o
[87/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/ScheduleDAGInstrs.cpp.o
[88/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/UnreachableBlockElim.cpp.o
[89/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetRegisterInfo.cpp.o
[90/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/WindowScheduler.cpp.o
[91/307] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/FunctionLoweringInfo.cpp.o
[92/307] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGFast.cpp.o
[93/307] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/InstrEmitter.cpp.o
[94/307] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGVLIW.cpp.o
[95/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TwoAddressInstructionPass.cpp.o
[96/307] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ResourcePriorityQueue.cpp.o
[97/307] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGRRList.cpp.o
[98/307] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGSDNodes.cpp.o
[99/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/RegAllocGreedy.cpp.o
[100/307] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/SelectionDAGDumper.cpp.o
[101/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/ModuloSchedule.cpp.o
[102/307] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/FastISel.cpp.o
[103/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/LiveDebugValues/VarLocBasedImpl.cpp.o
[104/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/SplitKit.cpp.o
[105/307] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/LiveDebugValues/InstrRefBasedImpl.cpp.o
[106/307] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/SelectionDAGISel.cpp.o
[107/307] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/DwarfDebug.cpp.o
[108/307] Building CXX object lib/CodeGen/AsmPrinter/CMakeFiles/LLVMAsmPrinter.dir/AsmPrinter.cpp.o
[109/307] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/SelectionDAGBuilder.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/126060