[PATCH] D96945: [InstCombine] Add simplification of two logical and/ors

[Jordan Rupprecht via Phabricator via llvm-commits]

rupprecht added a comment.

Here's a repro for the issue we're seeing. It only seems to be happening with msan enabled, so I'm not sure if this is just an msan bug, or a general miscompile that *happens* to trigger in this test when msan is enabled.

The source:

  #include <string>
  #include <variant>
  
  struct a {
    double b;
    double c;
    std::string d;
  };
  
  std::variant<std::pair<int, int>, std::string> e(a f) {
    double g = f.b, h = f.c;
    if (f.d == "y") {
      g *= 2.0;
      h *= 2.0;
    }
    int i(g);
    int k(h);
    if (i == 0) i = h;
    if (k == 0) k = i;
    if (k < i || i < 0) {
      std::string j;
      return j;
    }
    return std::make_pair(i, k);
  }
  
  int main() {
    auto j = e({1, 0, "x"});
    std::get<0>(j);
  }

To build/run it:

  $ clang++ \
    -O2 \
    -msse4.2 \
    -fsanitize=memory \
    -std=gnu++17 \
    -stdlib=libc++ \
    repro.cc \
    -o bug
  $ ./bug
  terminating with uncaught exception of type std::bad_variant_access: bad_variant_access

Thoughts on this example? If I follow correctly, at the `if (k < i || i < 0) {` check, both `k` and `i` should be 1, and that check should not trigger. Instead, it evaluates to true: the `std::get<0>(j)` triggers an exception, because the method return a `std::string`, not a `std::pair` after this patch.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D96945/new/

https://reviews.llvm.org/D96945