[all-commits] [llvm/llvm-project] 0107c9: [DAG] canCreateUndefOrPoison – mark fneg/fadd/fsub...

[Harrison Hao via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0107c9333cee3fb7af0dbffdce07422fe6b82bfa
      https://github.com/llvm/llvm-project/commit/0107c9333cee3fb7af0dbffdce07422fe6b82bfa
  Author: Harrison Hao <57025411+harrisonGPU at users.noreply.github.com>
  Date:   2025-06-03 (Tue, 03 Jun 2025)

  Changed paths:
    M llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
    A llvm/test/CodeGen/AMDGPU/freeze-binary.ll

  Log Message:
  -----------
  [DAG] canCreateUndefOrPoison – mark fneg/fadd/fsub/fmul/fdiv/frem as not poison generating (#142345)

After revisiting the LLVM Language Reference Manual, it is confirmed
that
plain floating-point operations (`fneg`, `fadd`, `fsub`, `fmul`, `fdiv`,
and `frem`)
propagate poison but do not inherently create new poison values. Thus, 
`SelectionDAG::canCreateUndefOrPoison` should return `false` for these 
operations by default.

Poison generation in FP instructions occurs only when specific fast-math
flags (`nnan`, `ninf`, or the collective fast) are present, as these
flags
explicitly convert NaN or Inf results into poison.

References:

- [`fneg` instruction
documentation](https://llvm.org/docs/LangRef.html#fneg-instruction)
- [`fadd` instruction
documentation](https://llvm.org/docs/LangRef.html#fadd-instruction)
- [`fsub` instruction
documentation](https://llvm.org/docs/LangRef.html#fsub-instruction)
- [`fmul` instruction
documentation](https://llvm.org/docs/LangRef.html#fmul-instruction)
- [`fdiv` instruction
documentation](https://llvm.org/docs/LangRef.html#fdiv-instruction)
- [`frem` instruction
documentation](https://llvm.org/docs/LangRef.html#frem-instruction)
- [Fast-Math Flags
documentation](https://llvm.org/docs/LangRef.html#fast-math-flags)



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