[all-commits] [llvm/llvm-project] b182b4: [CodeGen] Correctly classify/mark dead defs when a...

[Lucas Ramirez via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: b182b415d9b2447cf1fd7231ebe28a96cfd1f9af
      https://github.com/llvm/llvm-project/commit/b182b415d9b2447cf1fd7231ebe28a96cfd1f9af
  Author: Lucas Ramirez <11032120+lucas-rami at users.noreply.github.com>
  Date:   2026-09-08 (Tue, 08 Sep 2026)

  Changed paths:
    M llvm/include/llvm/CodeGen/RegisterPressure.h
    M llvm/lib/CodeGen/MachineScheduler.cpp
    M llvm/lib/CodeGen/RegisterPressure.cpp
    M llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
    M llvm/unittests/CodeGen/CMakeLists.txt
    A llvm/unittests/CodeGen/RegisterPressureTest.cpp

  Log Message:
  -----------
  [CodeGen] Correctly classify/mark dead defs when adjusting lane liveness (#215595)

Despite what the documentation of `adjustLaneLiveness` states, the
method never sets dead flags on dead def operands, even when missing
dead flags can later lead to machine verifier errors.

This makes the method identify dead definitions from definitions that
are initially thought to be alive, and makes it add a dead flag on the
last definition of a virtual register, matching the behavior expected by
the machine verifier (ref. "Instruction ending live segment on dead slot
has no dead flag").

`adjustLaneLiveness` and `detectDeadDefs` now also use the same
mechanism to identify dead definitions. It relies on comparing the
defined lanes of a definition with those that stay alive after it.



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