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

Sun Mar 23 04:30:18 PDT 2025

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `cross-project-tests-sie-ubuntu-dwarf5` running on `doug-worker-1b` while building `llvm` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/163/builds/15752

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
131.185 [222/8/79] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/RegisterCoalescer.cpp.o
136.792 [221/8/80] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/ScheduleDAGInstrs.cpp.o
137.123 [220/8/81] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/ShrinkWrap.cpp.o
137.167 [219/8/82] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TailDuplication.cpp.o
139.218 [218/8/83] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/SplitKit.cpp.o
139.513 [217/8/84] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/StackSlotColoring.cpp.o
140.797 [216/8/85] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/SwiftErrorValueTracking.cpp.o
143.770 [215/8/86] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TailDuplicator.cpp.o
144.686 [214/8/87] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetSchedule.cpp.o
145.678 [213/8/88] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o
FAILED: lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.o 
/opt/ccache/bin/g++ -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/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/lib/CodeGen -I/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/llvm/lib/CodeGen -I/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/include -I/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/llvm/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 -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 /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/llvm/lib/CodeGen/TargetInstrInfo.cpp
In file included from /usr/include/c++/11/cassert:44,
                 from /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/llvm/include/llvm/ADT/IntrusiveRefCntPtr.h:64,
                 from /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/llvm/include/llvm/Support/PGOOptions.h:17,
                 from /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/llvm/include/llvm/Target/TargetMachine.h:24,
                 from /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/llvm/lib/CodeGen/TargetInstrInfo.cpp:38:
/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/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’:
/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/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);
      |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/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>
/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/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,
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
147.224 [213/7/89] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/UnreachableBlockElim.cpp.o
148.923 [213/6/90] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetRegisterInfo.cpp.o
150.384 [213/5/91] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/VirtRegMap.cpp.o
152.095 [213/4/92] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TwoAddressInstructionPass.cpp.o
152.186 [213/3/93] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/VLIWMachineScheduler.cpp.o
152.268 [213/2/94] Building CXX object lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/XRayInstrumentation.cpp.o
155.954 [213/1/95] 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