[PATCH] D32433: Compute safety information in a much finer granularity.

[Daniel Berlin via Phabricator via llvm-commits]

dberlin added inline comments.


================
Comment at: llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp:1050
+  for (Instruction *ExitInst : SafetyInfo->EarlyExits)
+    if (!DT->dominates(&Inst, ExitInst))
+      return false;
----------------
efriedma wrote:
> This could be slow: if the two instructions are in the same basic block, dominates() will iterate over the whole block. And you don't attempt to prune the EarlyExits list, which could make LICM O(N^3) overall for a large loop with a single basic block.
> 
> I guess we'll see if it matters in practice.
Two  fixes, one short term we should do, one longer term

1. Let that dominates call take an OBB as an optional argument

2. Just provide global + local dominance ordering as an analysis that encapsulates both the OBB + DT solution, and remove that use of dominates in favor of the analysis.




Repository:
  rL LLVM

https://reviews.llvm.org/D32433