[PATCH] D83949: [TSan] Do not compound reads and writes when separated by atomics

[Marco Elver via Phabricator via llvm-commits]

melver added a comment.

In D83949#2155758 <https://reviews.llvm.org/D83949#2155758>, @dvyukov wrote:

> What would be an example of code where it matters?


For the kernel it doesn't matter, because we don't use builtin atomics (yet). The asm case works because it looks like a call.

For normal code, you could have something like:

  T0:
    x = load A  // data race
    atomic load acquire B // observes 1
    store A, ...
  
  T1:
    store A, ...
    atomic store release B, 1

If the current logic compounds this and TSAN only sees:

  T0:
    atomic load acquire B // observes 1
    store A, ...

we might miss the data race of the load on A. In practice, it probably doesn't really matter because T0 would probably load acquire spin on B or something better, and it'd be all in separate basic blocks.


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