[all-commits] [llvm/llvm-project] e81334: [LICM] Remove MaybePromotable set (PR50367)

[Nikita Popov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e81334a75401f3af3b10f64e307d705d97637a03
      https://github.com/llvm/llvm-project/commit/e81334a75401f3af3b10f64e307d705d97637a03
  Author: Nikita Popov <nikita.ppv at gmail.com>
  Date:   2021-05-18 (Tue, 18 May 2021)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LICM.cpp
    A llvm/test/Transforms/LICM/pr50367.ll

  Log Message:
  -----------
  [LICM] Remove MaybePromotable set (PR50367)

The MaybePromotable set keeps track of loads/stores for which
promotion was not attempted yet. Normally, any load/stores that
are promoted in the current iteration will be removed from this
set, because they naturally MustAlias with the promoted value.
However, if the source program has UB with metadata claiming that
a store is NoAlias, while it is actually MustAlias, and multiple
different pointers are promoted in the same iteration, it can
happen that a store is removed that is still in the MaybePromotable
set, causing a use-after-free.

While this could be fixed by explicitly invalidating values in
MaybePromotable in the LoopPromoter, I'm going with the more
radical option of dropping the set entirely here and check all
load/stores on each promotion iteration. As promotion, and especially
repeated promotion, are quite rare, this doesn't seem to have any
impact on compile-time.

Fixes https://bugs.llvm.org/show_bug.cgi?id=50367.