[all-commits] [llvm/llvm-project] ad9dad: [BasicAA] Bail out earlier for invalid shift amount

[Nikita Popov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: ad9dad93ff1237aed820bac8ec8e172e73af786d
      https://github.com/llvm/llvm-project/commit/ad9dad93ff1237aed820bac8ec8e172e73af786d
  Author: Nikita Popov <nikita.ppv at gmail.com>
  Date:   2021-03-27 (Sat, 27 Mar 2021)

  Changed paths:
    M llvm/lib/Analysis/BasicAliasAnalysis.cpp

  Log Message:
  -----------
  [BasicAA] Bail out earlier for invalid shift amount

Currently, we'd produce an incorrect decomposition, because we
already recursively called GetLinearExpression(), so the Scale=1,
Offset=0 will not necessarily be relative to the shl itself.

Now, this doesn't actually matter for functional correctness,
because such a shift is poison anyway, so its okay to return
an incorrect decomposition. It's still unnecessarily confusing
though, and we can easily avoid this by checking the bitwidth
earlier.