[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-debian-cpp20` running on `clang-debian-cpp20` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/108/builds/10765

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
89.957 [4730/17/1259] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/LegalizeIntegerTypes.cpp.o
89.973 [4729/17/1260] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/LegalizeTypes.cpp.o
89.988 [4728/17/1261] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/LegalizeTypesGeneric.cpp.o
90.004 [4727/17/1262] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/LegalizeVectorOps.cpp.o
90.022 [4726/17/1263] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/LegalizeVectorTypes.cpp.o
90.075 [4725/17/1264] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetSchedule.cpp.o
90.376 [4724/17/1265] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/StackSlotColoring.cpp.o
90.887 [4723/17/1266] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TailDuplicator.cpp.o
91.289 [4722/17/1267] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/UnreachableBlockElim.cpp.o
91.569 [4721/17/1268] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o
FAILED: lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o 
ccache /usr/bin/clang++-17 -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/vol/worker/clang-debian-cpp20/clang-debian-cpp20/build/lib/CodeGen -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/lib/CodeGen -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/build/include -I/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/include -Wno-deprecated-enum-enum-conversion -Wno-deprecated-declarations -Wno-deprecated-anon-enum-enum-conversion -Wno-ambiguous-reversed-operator -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++20  -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 /vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/lib/CodeGen/TargetInstrInfo.cpp
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/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());
      |                             ^~~~~~~~~~~~~~~~~
/vol/worker/clang-debian-cpp20/clang-debian-cpp20/llvm-project/llvm/lib/CodeGen/TargetInstrInfo.cpp:1021:35: note: passing argument to parameter 'InstrIdxForVirtReg' here
 1021 |     DenseMap<unsigned, unsigned> &InstrIdxForVirtReg,
      |                                   ^
1 error generated.
92.478 [4721/16/1269] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/SplitKit.cpp.o
94.329 [4721/15/1270] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/VirtRegMap.cpp.o
94.476 [4721/14/1271] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/VLIWMachineScheduler.cpp.o
95.058 [4721/13/1272] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TwoAddressInstructionPass.cpp.o
95.980 [4721/12/1273] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/XRayInstrumentation.cpp.o
97.891 [4721/11/1274] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/WindowScheduler.cpp.o
98.850 [4721/10/1275] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGFast.cpp.o
99.203 [4721/9/1276] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ResourcePriorityQueue.cpp.o
99.409 [4721/8/1277] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/FunctionLoweringInfo.cpp.o
99.433 [4721/7/1278] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/InstrEmitter.cpp.o
99.531 [4721/6/1279] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGVLIW.cpp.o
99.857 [4721/5/1280] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGSDNodes.cpp.o
101.190 [4721/4/1281] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGRRList.cpp.o
102.490 [4721/3/1282] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/FastISel.cpp.o
104.625 [4721/2/1283] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/LiveDebugValues/VarLocBasedImpl.cpp.o
110.053 [4721/1/1284] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/LiveDebugValues/InstrRefBasedImpl.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

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