[PATCH] D44766: Extend peeling to help invariant motion

[Eli Friedman via Phabricator via llvm-commits]

efriedma added inline comments.


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Comment at: lib/Transforms/Utils/LoopUnrollPeel.cpp:266
+        // If there is an instruction with invariant operands and unsafe to
+        // speculate - that is because of unreachable exit block prior to it.
+        // Peeling first iteration will prove the instruction is safe.
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This heuristic is a bit suspicious.  I'm not sure we always run LICM immediately before unrolling.  And even if we do, peeling won't help in a lot of situations; a load could alias another memory operation, or it might not dominate the loop latch.


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Comment at: lib/Transforms/Utils/LoopUnrollPeel.cpp:531
   BasicBlock *Latch = L->getLoopLatch();
-  BasicBlock *Exit = L->getUniqueExitBlock();
+  BasicBlock *Exit = L->getUniqueReachableExitBlock();
 
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This is really hacky.

There really isn't any reason we can't peel loops with multiple exits; it just isn't implemented yet.  Please fix it properly.


Repository:
  rL LLVM

https://reviews.llvm.org/D44766