[all-commits] [llvm/llvm-project] 94e4ee: [AMDGPU] Fixed crash in getLastMIForRegion when th...

[Dhruva Chakrabarti via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 94e4ee38aa3b7085409b72702437822b5cec9e4e
      https://github.com/llvm/llvm-project/commit/94e4ee38aa3b7085409b72702437822b5cec9e4e
  Author: Dhruva Chakrabarti <Dhruva.Chakrabarti at amd.com>
  Date:   2025-11-19 (Wed, 19 Nov 2025)

  Changed paths:
    M llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
    M llvm/test/CodeGen/AMDGPU/machine-scheduler-sink-trivial-remats.mir

  Log Message:
  -----------
  [AMDGPU] Fixed crash in getLastMIForRegion when the region is empty. (#168653)

PreRARematStage builds region live-outs if GCN trackers are enabled. If
rematerialization leads to empty regions, this can cause a crash because
of dereference of an invalid iterator in getLastMIForRegion. The fix is
to skip calling getLastMIForRegion for empty regions.

This patch fixes another bug in the same code region. getLastMIForRegion
calls skipDebugInstructionsBackward which may immediately return the
RegionEnd if it is not the begin instruction and it is a non-debug
instruction. That would imply considering an instruction that is outside
the relevant region. The fix is to always pass the previous of RegionEnd
to skipDebugInstructionsBackward.

This bug was found while using GCN trackers on the existing LIT test
machine-scheduler-sink-trivial-remats.mir. Here's the assertion failure.

llvm-project/llvm/include/llvm/ADT/ilist_iterator.h:168:
llvm::ilist_iterator<OptionsT, IsReverse, IsConst>::reference
llvm::ilist_iterator<OptionsT, IsReverse, IsConst>::operator*() const
[with OptionsT = llvm::ilist_detail::node_options<llvm::MachineInstr,
true, true, void, false, void>; bool IsReverse = false; bool IsConst =
false; llvm::ilist_iterator<OptionsT, IsReverse, IsConst>::reference =
llvm::MachineInstr&]: Assertion `!NodePtr->isKnownSentinel()' failed.



To unsubscribe from these emails, change your notification settings at https://github.com/llvm/llvm-project/settings/notifications