[PATCH] D15537: limit the number of instructions per block examined by dead store elimination

[Philip Reames via llvm-commits]

reames added a comment.

I just want to make sure I understand the big picture view of this change.  I'm going to try to summarize, please correct me if I'm wrong.

Today, we will walk back through the list of defs/clobbers provided by MDA (within a single block) without limit in DSE.  Internally, MDA will only find defs/clobbers which are within a limited distance of each other.  As a result, a series of adjacent clobbers will be scanned, but the same series of adjacent clobbers with a single long break of non-memory related instructions will not be.  Right?

With the patch, we will walk backwards a fixed distance (in number of instructions) considering any def/clobber we see in that window.

Is that a correct summary?

(p.s. Using the same default value from the original implementation with the new one seems highly suspect since the old implementation would have been much more aggressive in practice..)


https://reviews.llvm.org/D15537