[all-commits] [llvm/llvm-project] c08333: [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: c08333444a5e72c3a6d093b28057df390c41c601
      https://github.com/llvm/llvm-project/commit/c08333444a5e72c3a6d093b28057df390c41c601
  Author: Petar Jovanovic <petar.jovanovic at amd.com>
  Date:   2026-09-30 (Wed, 30 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: 68ddfa2354e688c53162c6a495a87a69fbd4058e
      https://github.com/llvm/llvm-project/commit/68ddfa2354e688c53162c6a495a87a69fbd4058e
  Author: Petar Jovanovic <petar.jovanovic at amd.com>
  Date:   2026-09-30 (Wed, 30 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/20a8856c3b77...68ddfa2354e6

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