[all-commits] [llvm/llvm-project] fa86d5: [SlotIndexes] Add queries for stale indexes

[Petar Jovanovic via All-commits]

  Branch: refs/heads/users/petar-jovanovic/ldv-stale-slot-indexes
  Home:   https://github.com/llvm/llvm-project
  Commit: fa86d52cf15f30e7890b38f696e1c21eb6017b7e
      https://github.com/llvm/llvm-project/commit/fa86d52cf15f30e7890b38f696e1c21eb6017b7e
  Author: Petar Jovanovic <petar.jovanovic at amd.com>
  Date:   2026-09-18 (Fri, 18 Sep 2026)

  Changed paths:
    M llvm/include/llvm/CodeGen/SlotIndexes.h
    M llvm/lib/CodeGen/SlotIndexes.cpp
    M llvm/unittests/CodeGen/CMakeLists.txt
    A llvm/unittests/CodeGen/SlotIndexesTest.cpp

  Log Message:
  -----------
  [SlotIndexes] Add queries for stale indexes

An erased instruction leaves its index list entry in place, making the
index indistinguishable from a block boundary entry. Add
isBlockBoundaryIndex() and isStaleIndex() to tell the two apart, and
canonicalizeIndex() to resolve a stale index to the closest preceding
instruction's register slot, or the block start if none survives.

NFC. No caller yet. LiveDebugVariables is next.


  Commit: 137285bac21f1cc947eca3cf27cfe9024609af6f
      https://github.com/llvm/llvm-project/commit/137285bac21f1cc947eca3cf27cfe9024609af6f
  Author: Petar Jovanovic <petar.jovanovic at amd.com>
  Date:   2026-09-18 (Fri, 18 Sep 2026)

  Changed paths:
    M llvm/include/llvm/CodeGen/LiveDebugVariables.h
    M llvm/lib/CodeGen/LiveDebugVariables.cpp
    M llvm/lib/CodeGen/RegAllocGreedy.cpp
    M llvm/test/CodeGen/X86/debug-spilled-snippet.ll
    M llvm/test/CodeGen/X86/debug-spilled-snippet.mir
    A llvm/test/DebugInfo/AMDGPU/live-debug-vars-stale-slot-indexes.ll
    M llvm/test/DebugInfo/MIR/X86/live-debug-vars-unused-arg-debugonly.mir

  Log Message:
  -----------
  [LiveDebugVariables] Repair stale SlotIndexes

The analysis keeps its indexes from before the first register allocator
until DBG_VALUEs are emitted, by which point passes in between have
erased some of the instructions they point at. Resolve them at the
start of each allocator run and before emitting.

SlotIndexes can then reclaim the entries of erased instructions without
sparing the ones held here, which would have made generated code depend
on -g. Emitted locations are unchanged, except that intervals resolving
to one position now emit a single DBG_VALUE rather than identical
consecutive ones.


Compare: https://github.com/llvm/llvm-project/compare/3d7113844252...137285bac21f

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