[PATCH] D63948: [SLP] Limit compilation time of look-ahead operand reordering heuristic.

Mon Jul 1 12:12:37 PDT 2019

ABataev added a comment.

In D63948#1565229 <https://reviews.llvm.org/D63948#1565229>, @vporpo wrote:

> Not sure what kind of test would be suitable for this change. It simply restricts the look-ahead heuristic to not visit more than 2 operands and 2 uses, which is not something visible in the output IR.

You still need the test that demonstrates the effect of this change. You need to show that the option really affects the vectorization somehow.

================
Comment at: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp:921
+      for (unsigned OpIdx1 = 0,
+                    NumOperands1 = std::min(I1->getNumOperands(),
+                                            LookAheadOperandsBudget.getValue());
----------------
vporpo wrote:
> ABataev wrote:
> > Do you really need this limit?
> Yes, because it could be a call /phi instruction with many operands.
Does this really the cause of the problems? It would be good to see some additional investigation if this is really required.

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  https://reviews.llvm.org/D63948/new/

https://reviews.llvm.org/D63948