[llvm-branch-commits] [llvm] release/21.x: [HEXAGON] [MachinePipeliner] Fix the DAG in case of dependent phis. (#135925) (PR #170749)

[Brian Cain via llvm-branch-commits]

androm3da wrote:

@iajbar  @quic-asaravan  could there be some other dependencies that need to be cherry-picked for this fix?

```
2025-12-04T21:46:58.3210476Z ******************** TEST 'LLVM :: CodeGen/Hexagon/phi-elim.ll' FAILED ********************
2025-12-04T21:46:58.3213147Z Exit Code: 134
2025-12-04T21:46:58.3213736Z 
2025-12-04T21:46:58.3214072Z Command Output (stderr):
2025-12-04T21:46:58.3215568Z --
2025-12-04T21:46:58.3217037Z /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/llc -mtriple=hexagon < /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/CodeGen/Hexagon/phi-elim.ll # RUN: at line 1
2025-12-04T21:46:58.3219195Z + /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/llc -mtriple=hexagon
2025-12-04T21:46:58.3221933Z llc: /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/lib/CodeGen/ScheduleDAG.cpp:522: void llvm::ScheduleDAGTopologicalSort::InitDAGTopologicalSorting(): Assertion `Node2Index[SU.NodeNum] > Node2Index[PD.getSUnit()->NodeNum] && "Wrong topological sorting"' failed.
2025-12-04T21:46:58.3224463Z PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
2025-12-04T21:46:58.3225351Z Stack dump:
2025-12-04T21:46:58.3226149Z 0.	Program arguments: /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/llc -mtriple=hexagon
2025-12-04T21:46:58.3227183Z 1.	Running pass 'Function Pass Manager' on module '<stdin>'.
2025-12-04T21:46:58.3227888Z 2.	Running pass 'Modulo Software Pipelining' on function '@f0'
2025-12-04T21:46:58.3229721Z  #0 0x0000578003f045c8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/lib/Support/Unix/Signals.inc:834:13
2025-12-04T21:46:58.3231779Z  #1 0x0000578003f01cd5 llvm::sys::RunSignalHandlers() /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/lib/Support/Signals.cpp:105:18
2025-12-04T21:46:58.3233408Z  #2 0x0000578003f05391 SignalHandler(int, siginfo_t*, void*) /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/lib/Support/Unix/Signals.inc:426:38
2025-12-04T21:46:58.3234537Z  #3 0x00007b8e5cce1330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
2025-12-04T21:46:58.3235243Z  #4 0x00007b8e5cd3ab2c pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x9eb2c)
2025-12-04T21:46:58.3235996Z  #5 0x00007b8e5cce127e raise (/lib/x86_64-linux-gnu/libc.so.6+0x4527e)
2025-12-04T21:46:58.3236627Z  #6 0x00007b8e5ccc48ff abort (/lib/x86_64-linux-gnu/libc.so.6+0x288ff)
2025-12-04T21:46:58.3237500Z  #7 0x00007b8e5ccc481b (/lib/x86_64-linux-gnu/libc.so.6+0x2881b)
2025-12-04T21:46:58.3238107Z  #8 0x00007b8e5ccd7517 (/lib/x86_64-linux-gnu/libc.so.6+0x3b517)
2025-12-04T21:46:58.3239737Z  #9 0x00005780031ce0d6 llvm::ScheduleDAGTopologicalSort::InitDAGTopologicalSorting() /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/lib/CodeGen/ScheduleDAG.cpp:0:0
2025-12-04T21:46:58.3241434Z #10 0x0000578002f8e5e1 llvm::SwingSchedulerDAG::schedule() /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/lib/CodeGen/MachinePipeliner.cpp:710:3
2025-12-04T21:46:58.3243241Z #11 0x0000578002f8cf7f llvm::MachinePipeliner::swingModuloScheduler(llvm::MachineLoop&) /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/lib/CodeGen/MachinePipeliner.cpp:635:7
2025-12-04T21:46:58.3249321Z #12 0x0000578002f8aff2 llvm::MachinePipeliner::scheduleLoop(llvm::MachineLoop&) /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/lib/CodeGen/MachinePipeliner.cpp:434:15

```

https://github.com/llvm/llvm-project/pull/170749