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

Sun Mar 23 04:43:42 PDT 2025

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-armv7-lnt` running on `linaro-clang-armv7-lnt` while building `llvm` at step 6 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/77/builds/10402

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

```
Step 6 (build stage 1) failure: 'ninja' (failure)
...
[114/906] Building CXX object lib/Target/SystemZ/CMakeFiles/LLVMSystemZCodeGen.dir/SystemZCallingConv.cpp.o
[115/906] Building CXX object lib/Target/PowerPC/AsmParser/CMakeFiles/LLVMPowerPCAsmParser.dir/PPCAsmParser.cpp.o
[116/906] Building CXX object lib/Target/SystemZ/CMakeFiles/LLVMSystemZCodeGen.dir/SystemZCopyPhysRegs.cpp.o
[117/906] Building CXX object lib/Target/SystemZ/CMakeFiles/LLVMSystemZCodeGen.dir/SystemZHazardRecognizer.cpp.o
[118/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64ConditionalCompares.cpp.o
[119/906] Building CXX object lib/Target/SystemZ/CMakeFiles/LLVMSystemZCodeGen.dir/SystemZElimCompare.cpp.o
[120/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64CondBrTuning.cpp.o
[121/906] Building CXX object lib/CodeGen/GlobalISel/CMakeFiles/LLVMGlobalISel.dir/MachineIRBuilder.cpp.o
[122/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64DeadRegisterDefinitionsPass.cpp.o
[123/906] 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-armv7-lnt/stage1/lib/CodeGen -I/home/tcwg-buildbot/worker/clang-armv7-lnt/llvm/llvm/lib/CodeGen -I/home/tcwg-buildbot/worker/clang-armv7-lnt/stage1/include -I/home/tcwg-buildbot/worker/clang-armv7-lnt/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-armv7-lnt/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.
[124/906] Building CXX object lib/Target/SystemZ/CMakeFiles/LLVMSystemZCodeGen.dir/SystemZFrameLowering.cpp.o
[125/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/GISel/AArch64PostSelectOptimize.cpp.o
[126/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64CallingConvention.cpp.o
[127/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64CleanupLocalDynamicTLSPass.cpp.o
[128/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64BranchTargets.cpp.o
[129/906] Building CXX object lib/CodeGen/GlobalISel/CMakeFiles/LLVMGlobalISel.dir/Utils.cpp.o
[130/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64A57FPLoadBalancing.cpp.o
[131/906] Building CXX object lib/Target/SystemZ/CMakeFiles/LLVMSystemZCodeGen.dir/SystemZAsmPrinter.cpp.o
[132/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64CollectLOH.cpp.o
[133/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64ExpandPseudoInsts.cpp.o
[134/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/GISel/AArch64CallLowering.cpp.o
[135/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64FalkorHWPFFix.cpp.o
[136/906] Building CXX object lib/CodeGen/MIRParser/CMakeFiles/LLVMMIRParser.dir/MIParser.cpp.o
[137/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64ConditionOptimizer.cpp.o
[138/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/GISel/AArch64O0PreLegalizerCombiner.cpp.o
[139/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/GISel/AArch64PostLegalizerCombiner.cpp.o
[140/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/GISel/AArch64PostLegalizerLowering.cpp.o
[141/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64A53Fix835769.cpp.o
[142/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/GISel/AArch64PreLegalizerCombiner.cpp.o
[143/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/GISel/AArch64LegalizerInfo.cpp.o
[144/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64CompressJumpTables.cpp.o
[145/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64AsmPrinter.cpp.o
[146/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64MIPeepholeOpt.cpp.o
[147/906] Building CXX object lib/CodeGen/GlobalISel/CMakeFiles/LLVMGlobalISel.dir/LegalizerHelper.cpp.o
[148/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64MachineScheduler.cpp.o
[149/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64LowerHomogeneousPrologEpilog.cpp.o
[150/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64MacroFusion.cpp.o
[151/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64PBQPRegAlloc.cpp.o
[152/906] Building CXX object lib/Target/AArch64/CMakeFiles/LLVMAArch64CodeGen.dir/AArch64MachineFunctionInfo.cpp.o
[153/906] Building CXX object lib/Target/AArch64/AsmParser/CMakeFiles/LLVMAArch64AsmParser.dir/AArch64AsmParser.cpp.o

```

</details>

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