Nikita Popov 5a4c6f9799 [Loads] Check context instruction for context-sensitive derefability (#109277) ...

If a dereferenceability fact is provided through `!dereferenceable` (or
similar), it may only hold on the given control flow path. When we use
`isSafeToSpeculativelyExecute()` to check multiple instructions, we
might make use of `!dereferenceable` information that does not hold at
the speculation target. This doesn't happen when speculating
instructions one by one, because `!dereferenceable` will be dropped
while speculating.

Fix this by checking whether the instruction with `!dereferenceable`
dominates the context instruction. If this is not the case, it means we
are speculating, and cannot guarantee that it holds at the speculation
target.

Fixes https://github.com/llvm/llvm-project/issues/108854.

2024-09-23 09:13:09 +02:00

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