[PATCH] D18062: Fix Load Control Dependence in MemCpy Generation

Hal Finkel via llvm-commits llvm-commits at lists.llvm.org
Wed Mar 23 12:02:23 PDT 2016

hfinkel added a comment.

In http://reviews.llvm.org/D18062#381709, @niravd wrote:

> Ping. Your thoughts on this Hal?

This is quite interesting. The question is: Can we guarantee that all data dependencies are also encoded as chain dependencies? If so, then I'm happy with this -- although I'd also like some loud comments (maybe in include/llvm/CodeGen/ISDOpcodes.h), and ideally some verification code which can be enabled under expensive checks.

My worry here is not just about what we generate, but about what FindBetterChain might do. It would need to specifically not remove a chain dependency that was present to protect/represent a value dependency.

> ppc64-align-long-double.ll now may see multiple serializations of its stores

What does this mean? I see you've put in CHECK-DAGs, but do you mean the order has changed or that there are now multiple stores?


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