[PATCH] D144057: [GVN] permit GVN of non-local loads for ASAN unless undef is produced

[Nick Desaulniers via Phabricator via llvm-commits]

nickdesaulniers added a comment.

In D144057#4128142 <https://reviews.llvm.org/D144057#4128142>, @nikic wrote:

> I don't think this is right as implemented. Imagine you have `if (...) { store v, p } x = load p`. GVN would convert this to something like `x = phi(v, undef)`. With asan, we want this to report if the if is not taken. However, I believe that your checks will permit the transform, because the load folding result is not literally undef (but is still undef on one path).

Is this what you're imagining? https://godbolt.org/z/Pc3YezE44

Seems like ASAN already misses that? In this case, we go to replace the load with alloca, so adding a check remedies that case. But it doesn't change the fact that asan misses that C test case.


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