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

Sun Mar 23 04:30:27 PDT 2025

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ml-opt-dev-x86-64` running on `ml-opt-dev-x86-64-b2` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/137/builds/15677

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
92.002 [1759/64/1995] Building CXX object lib/Target/CMakeFiles/LLVMTarget.dir/TargetMachineC.cpp.o
92.022 [1758/64/1996] Building CXX object tools/llvm-exegesis/lib/CMakeFiles/LLVMExegesis.dir/CodeTemplate.cpp.o
92.042 [1757/64/1997] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/GISel/AArch64GlobalISelUtils.cpp.o
92.094 [1756/64/1998] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/GISel/AArch64RegisterBankInfo.cpp.o
92.170 [1755/64/1999] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64Arm64ECCallLowering.cpp.o
92.702 [1754/64/2000] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/MachineOutliner.cpp.o
92.792 [1753/64/2001] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGVLIW.cpp.o
93.026 [1752/64/2002] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/ScheduleDAGInstrs.cpp.o
93.254 [1751/64/2003] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/VLIWMachineScheduler.cpp.o
93.274 [1750/64/2004] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o
FAILED: lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o 
ccache /usr/bin/c++ -DCPUINFO_SUPPORTED_PLATFORM=1 -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/b/ml-opt-dev-x86-64-b1/build/lib/CodeGen -I/b/ml-opt-dev-x86-64-b1/llvm-project/llvm/lib/CodeGen -I/b/ml-opt-dev-x86-64-b1/build/include -I/b/ml-opt-dev-x86-64-b1/llvm-project/llvm/include -isystem /tmp/tflitebuild/tensorflow/include -isystem /tmp/tflitebuild/eigen/include/eigen3 -isystem /tmp/tflitebuild/abseil-cpp/include -isystem /tmp/tflitebuild/flatbuffers/include -isystem /tmp/tflitebuild/gemmlowp/include/gemmlowp -isystem /tmp/tflitebuild/ml_dtypes/src/ml_dtypes -isystem /tmp/tflitebuild/ml_dtypes/src/ml_dtypes/ml_dtypes -isystem /tmp/tflitebuild/ruy/include -isystem /tmp/tflitebuild/cpuinfo/include -isystem /tmp/tflitebuild/ARM_NEON_2_x86_SSE/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -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 -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -DEIGEN_NEON_GEBP_NR=4 -DTFL_STATIC_LIBRARY_BUILD -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 /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/lib/CodeGen/TargetInstrInfo.cpp
In file included from /usr/include/c++/10/cassert:44,
                 from /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/include/llvm/ADT/IntrusiveRefCntPtr.h:64,
                 from /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/include/llvm/Support/PGOOptions.h:17,
                 from /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/include/llvm/Target/TargetMachine.h:24,
                 from /b/ml-opt-dev-x86-64-b1/llvm-project/llvm/lib/CodeGen/TargetInstrInfo.cpp:38:
/b/ml-opt-dev-x86-64-b1/llvm-project/llvm/lib/CodeGen/TargetInstrInfo.cpp: In member function ‘virtual void llvm::TargetInstrInfo::genAlternativeCodeSequence(llvm::MachineInstr&, unsigned int, llvm::SmallVectorImpl<llvm::MachineInstr*>&, llvm::SmallVectorImpl<llvm::MachineInstr*>&, llvm::DenseMap<llvm::Register, unsigned int>&) const’:
/b/ml-opt-dev-x86-64-b1/llvm-project/llvm/lib/CodeGen/TargetInstrInfo.cpp:1487:46: warning: comparison of unsigned expression in ‘>= 0’ is always true [-Wtype-limits]
 1487 |         assert(IndexedReg.index() - MaxWidth >= 0);
      |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
/b/ml-opt-dev-x86-64-b1/llvm-project/llvm/lib/CodeGen/TargetInstrInfo.cpp:1514:29: error: cannot convert ‘llvm::DenseMap<llvm::Register, unsigned int>’ to ‘llvm::DenseMap<unsigned int, unsigned int>&’
 1514 |                             InstIdxForVirtReg, Root.getOperand(0).getReg());
      |                             ^~~~~~~~~~~~~~~~~
      |                             |
      |                             llvm::DenseMap<llvm::Register, unsigned int>
/b/ml-opt-dev-x86-64-b1/llvm-project/llvm/lib/CodeGen/TargetInstrInfo.cpp:1021:35: note:   initializing argument 6 of ‘void llvm::TargetInstrInfo::reduceAccumulatorTree(llvm::SmallVectorImpl<llvm::Register>&, llvm::SmallVectorImpl<llvm::MachineInstr*>&, llvm::MachineFunction&, llvm::MachineInstr&, llvm::MachineRegisterInfo&, llvm::DenseMap<unsigned int, unsigned int>&, llvm::Register) const’
 1021 |     DenseMap<unsigned, unsigned> &InstrIdxForVirtReg,
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
93.353 [1750/63/2005] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64ExpandImm.cpp.o
93.958 [1750/62/2006] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/RegisterCoalescer.cpp.o
94.424 [1750/61/2007] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/SplitKit.cpp.o
95.138 [1750/60/2008] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ResourcePriorityQueue.cpp.o
95.878 [1750/59/2009] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/MachineVerifier.cpp.o
96.205 [1750/58/2010] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/MIRPrinter.cpp.o
98.054 [1750/57/2011] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/RegAllocGreedy.cpp.o
98.459 [1750/56/2012] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGFast.cpp.o
99.121 [1750/55/2013] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TwoAddressInstructionPass.cpp.o
100.352 [1750/54/2014] Building CXX object lib/Object/CMakeFiles/LLVMObject.dir/IRSymtab.cpp.o
100.990 [1750/53/2015] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/MachineScheduler.cpp.o
102.091 [1750/52/2016] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/FunctionLoweringInfo.cpp.o
103.107 [1750/51/2017] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/InstrEmitter.cpp.o
104.138 [1750/50/2018] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGSDNodes.cpp.o
104.498 [1750/49/2019] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/SelectionDAGDumper.cpp.o
104.953 [1750/48/2020] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/ScheduleDAGRRList.cpp.o
105.035 [1750/47/2021] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/WindowScheduler.cpp.o
106.074 [1750/46/2022] Building CXX object lib/CodeGen/GlobalISel/CMakeFiles/LLVMGlobalISel.dir/MachineIRBuilder.cpp.o
111.114 [1750/45/2023] Building CXX object lib/CodeGen/GlobalISel/CMakeFiles/LLVMGlobalISel.dir/Utils.cpp.o
111.741 [1750/44/2024] Building CXX object lib/CodeGen/SelectionDAG/CMakeFiles/LLVMSelectionDAG.dir/FastISel.cpp.o

```

</details>

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