[PATCH] D10386: [LAA] Merge memchecks for accesses separated by a constant offset

[Adam Nemet]

anemet added a comment.

Hi Silviu,

In http://reviews.llvm.org/D10386#205474, @sbaranga wrote:

> Looking at the logic in analyzeLoops:
>
> In order to need memory checks, first we need Accesses.isDependencyCheckNeeded() to evaluate to true.
>  Since we need an unknown dependence between two objects to get into the 'veto' case, it follows that areDepsSafe will return false (we have al least one unknown dependence).
>
> This causes us to take the "!CanVecMem && DepChecker.shouldRetryWithRuntimeCheck()" branch and reset the dependence checks, which in turn will cause us to not group pointers.


shouldRetry... should only be set if we didn't find a constant distance between the accesses.  This is why I said earlier that:

The problem is that we can have unknown distance between pointers of the same underlying object also if the stride is unknown (look for the return Dependence::Unknown before the ShouldRetryWithRuntimeCheck in isDependent). In this case we don't give up on dependence analysis so your flag would still be true.

Was something unclear about this?  I can help to come up with a testcase for this if that helps.

Adam


Repository:
  rL LLVM

http://reviews.llvm.org/D10386