[PATCH] D75840: [ExpandMemCmp] Improve non-equality comparisons with zero.

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

Side note: I was wondering what these patterns look like in DAG/IR, and why we're missing them, so:
D75961 <https://reviews.llvm.org/D75961>

We could argue that it's worth solving these more generally in DAGCombiner, but if we can produce the optimal code here without too much effort, that's good too.



================
Comment at: llvm/lib/CodeGen/ExpandMemCmp.cpp:397
+  Cmp = Builder.CreateICmp(
+      ICmpInst::getUnsignedPredicate(ZeroCmpKind), Loads.Lhs, Loads.Rhs);
+
----------------
That looks like the right fix, but it could use a comment so we'll remember why. Something like this:
  // The result of memcmp is a signed value, so the relational 
  // compare kind predicate is always signed. But the byte
  // comparison used within memcmp is always unsigned.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D75840/new/

https://reviews.llvm.org/D75840