[PATCH] D72929: [SCEV] Swap guards estimation sequence. NFC

[Daniil Fukalov via Phabricator via llvm-commits]

dfukalov created this revision.
dfukalov added reviewers: skatkov, sanjoy, mkazantsev.
Herald added subscribers: javed.absar, hiraditya.
Herald added a project: LLVM.

Loop unroll spends a lot of time in SCEVs processing in case when a function
contains hundreds of simple 'for' loops with a quite complex arrays indexes like

  for (int i = 0; i < 8; ++i) {
    for (int j = 0; j < 32; ++j) {
      C[j*8+i] = B[j*32+i+128] + A[i*64+128];
    }
  }
  for (int i = 0; i < 8; ++i) {
    for (int j = 0; j < 8; ++j) {
      for (int k = 0; k < 32; ++k) {
        D[k*64+i*8+j] = D[k*64+i*8+j] + E[i+16] * C[k*8+j+256];
      }
    }
  }

The patch improves loop unroll speed since isLoopBackedgeGuardedByCond takes
much less time than isLoopEntryGuardedByCond in the edge case.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72929

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp


Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -9222,9 +9222,9 @@
       !isAvailableAtLoopEntry(SplitRHS.first, MDL))
     return false;
 
-  return isLoopEntryGuardedByCond(MDL, Pred, SplitLHS.first, SplitRHS.first) &&
-         isLoopBackedgeGuardedByCond(MDL, Pred, SplitLHS.second,
-                                     SplitRHS.second);
+  return isLoopBackedgeGuardedByCond(MDL, Pred, SplitLHS.second,
+                                     SplitRHS.second) &&
+         isLoopEntryGuardedByCond(MDL, Pred, SplitLHS.first, SplitRHS.first);
 }
 
 bool ScalarEvolution::isKnownPredicate(ICmpInst::Predicate Pred,


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