[all-commits] [llvm/llvm-project] db6bee: [RISCV] Fix miscompile in SExtWRemoval due to earl...

[Philip Reames via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: db6bee5fec0d7fdfc18005c5c5ccd15f1ede945d
      https://github.com/llvm/llvm-project/commit/db6bee5fec0d7fdfc18005c5c5ccd15f1ede945d
  Author: Philip Reames <preames at rivosinc.com>
  Date:   2023-02-08 (Wed, 08 Feb 2023)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVSExtWRemoval.cpp
    M llvm/test/CodeGen/RISCV/sextw-removal.ll

  Log Message:
  -----------
  [RISCV] Fix miscompile in SExtWRemoval due to early return ignoring other sources

This code is walking back through a worklist of sources. All of the sources need to be sign extending for the result to be true. We had a case which returned rather than continued, which causes a miscompile when another source was not sign extended. The flawed logic was introduced in Dec 22, by change 844430bcc377.

This was recently exposed in a stage2 build of llvm-tablegen when we switched from using llvm::Optional to std::optional. The stars aligned in just the wrong way, and we started actively miscompiling idiomatic optional usage. std::optional<uint32_t> appears to use the top 32 bits of the word on RV64 for its tag.

Differential Revision: https://reviews.llvm.org/D143594