[all-commits] [llvm/llvm-project] 0a8acd: [DAG] ComputeNumSignBits - ISD::EXTRACT_ELEMENT ne...

[Miguel Saldivar via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0a8acd2eb2aff0edd610fc3ec14b32bee446656f
      https://github.com/llvm/llvm-project/commit/0a8acd2eb2aff0edd610fc3ec14b32bee446656f
  Author: Miguel Saldivar <miguel.saldivar at hpe.com>
  Date:   2025-08-26 (Tue, 26 Aug 2025)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
    A llvm/test/CodeGen/AMDGPU/pr155452.ll

  Log Message:
  -----------
  [DAG] ComputeNumSignBits - ISD::EXTRACT_ELEMENT needs to return at least 1 (#155455)

When going through the ISD::EXTRACT_ELEMENT case, `KnownSign - rIndex *
BitWidth`
could produce a negative. When a negative is produced, the lower bound
of the `std::clamp` is returned. Change that lower bound to one to avoid
potential underflows, because the expectation is that
`ComputeNumSignBits`
should always return at least 1.

Fixes #155452.



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