llvm-project

cd844892 - [Loads] Only allow replacement with derefable constant global (#217350)

[Loads] Only allow replacement with derefable constant global (#217350) isPointerAlwaysReplaceable() currently allows replacing with Constants that are dereferenceable for at least one byte. This patch further restricts this carveout to cases where the Constant is based on a constant global. This fixes the case from #59679. In that case, the replacement is between a noalias pointer and a dereferenceable global. After the replacement, the noalias pointer is assumed to no longer alias with the replaced global write, resulting in a miscompile. The remaining carveout for constant globals is still not correct, but I think there's less issues we can encounter in the read-only case, and we have to support this for vtable assumptions to work. Fixes https://github.com/llvm/llvm-project/issues/59679.