[PATCH] D60047: [CaptureTracking] Pointer comparisons cannot escape

[Sanjoy Das via Phabricator via llvm-commits]

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Things that are UB in C++ are not necessarily UB in LLVM.  For instance you could capture a pointer by doing something like this:

  int global;
  
  void f() {
    int* ptr = new int;
  
    // Probably UB in C++?  But not UB in LLVM if the GEP is not
    // an inbounds GEP.
    if ((ptr+4096) == &global) {
      intptr_t addr = ((intptr_t)&global) - 4096;
      escape((int*)addr)
    }
  }



> However, I found that since inserting these null checks, escape analysis suffers badly because all icmp instructions are seen as captures.motivation:

A more extreme version of the example above could be written to just use a comparison against `null`:

  void f() {
    int* ptr = new int;
    if ((ptr-4096) == nullptr) {
      escape((int*)4096)
    }
  }


Repository:
  rL LLVM

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  https://reviews.llvm.org/D60047/new/

https://reviews.llvm.org/D60047