[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 `polly-arm-linux` running on `hexagon-build-02` while building `llvm` at step 5 "build".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/90/builds/5110

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

```
Step 5 (build) failure: 'ninja -j16' (failure)
...
[660/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/StackSlotColoring.cpp.o
[661/4288] Building CXX object lib/Transforms/IPO/CMakeFiles/LLVMipo.dir/AttributorAttributes.cpp.o
[662/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetOptionsImpl.cpp.o
[663/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetFrameLoweringImpl.cpp.o
[664/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetSubtargetInfo.cpp.o
[665/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/SwitchLoweringUtils.cpp.o
[666/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/StackProtector.cpp.o
[667/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/ValueTypes.cpp.o
[668/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TailDuplicator.cpp.o
[669/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o
FAILED: lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o 
/local/clang+llvm-12.0.0-x86_64-linux-gnu-ubuntu-16.04/bin/clang++ -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/local/mnt/workspace/bots/hexagon-build-02/polly-arm-linux/llvm.obj/lib/CodeGen -I/local/mnt/workspace/bots/hexagon-build-02/polly-arm-linux/llvm.src/llvm/lib/CodeGen -I/local/mnt/workspace/bots/hexagon-build-02/polly-arm-linux/llvm.obj/include -I/local/mnt/workspace/bots/hexagon-build-02/polly-arm-linux/llvm.src/llvm/include -stdlib=libc++ -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 -ffunction-sections -fdata-sections -O3 -DNDEBUG  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -std=c++17 -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 /local/mnt/workspace/bots/hexagon-build-02/polly-arm-linux/llvm.src/llvm/lib/CodeGen/TargetInstrInfo.cpp
/local/mnt/workspace/bots/hexagon-build-02/polly-arm-linux/llvm.src/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<llvm::Register, [...]>'
                            InstIdxForVirtReg, Root.getOperand(0).getReg());
                            ^~~~~~~~~~~~~~~~~
/local/mnt/workspace/bots/hexagon-build-02/polly-arm-linux/llvm.src/llvm/lib/CodeGen/TargetInstrInfo.cpp:1021:35: note: passing argument to parameter 'InstrIdxForVirtReg' here
    DenseMap<unsigned, unsigned> &InstrIdxForVirtReg,
                                  ^
1 error generated.
[670/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetSchedule.cpp.o
[671/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetLoweringObjectFileImpl.cpp.o
[672/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/UnreachableBlockElim.cpp.o
[673/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetLoweringBase.cpp.o
[674/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/WasmEHPrepare.cpp.o
[675/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetRegisterInfo.cpp.o
[676/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetPassConfig.cpp.o
[677/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/LiveDebugValues/LiveDebugValues.cpp.o
[678/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/XRayInstrumentation.cpp.o
[679/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/VirtRegMap.cpp.o
[680/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TypePromotion.cpp.o
[681/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/VLIWMachineScheduler.cpp.o
[682/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TwoAddressInstructionPass.cpp.o
[683/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/WinEHPrepare.cpp.o
[684/4288] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/WindowScheduler.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

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