Revert "[SCEV] Look at backedge dominating conditions."

This leads to terribly slow compile times under MSAN. More discussion
on the commit thread of r233447.

llvm-svn: 233529

1 files changed, 0 insertions, 40 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 26b468013c6..4e713fb1218 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6686,46 +6686,6 @@ ScalarEvolution::isLoopBackedgeGuardedByCond(const Loop *L,
                     LoopContinuePredicate->getSuccessor(0) != L->getHeader()))
     return true;
 
-  // If the loop is not reachable from the entry block, we risk running into an
-  // infinite loop as we walk up into the dom tree.  These loops do not matter
-  // anyway, so we just return a conservative answer when we see them.
-  if (!DT->isReachableFromEntry(L->getHeader()))
-    return false;
-
-  for (DomTreeNode *DTN = (*DT)[Latch], *HeaderDTN = (*DT)[L->getHeader()];
-       DTN != HeaderDTN;
-       DTN = DTN->getIDom()) {
-
-    assert(DTN && "should reach the loop header before reaching the root!");
-
-    BasicBlock *BB = DTN->getBlock();
-    BasicBlock *PBB = BB->getSinglePredecessor();
-    if (!PBB)
-      continue;
-
-    BranchInst *ContinuePredicate = dyn_cast<BranchInst>(PBB->getTerminator());
-    if (!ContinuePredicate || !ContinuePredicate->isConditional())
-      continue;
-
-    Value *Condition = ContinuePredicate->getCondition();
-
-    // If we have an edge `E` within the loop body that dominates the only
-    // latch, the condition guarding `E` also guards the backedge.  This
-    // reasoning works only for loops with a single latch.
-
-    BasicBlockEdge DominatingEdge(PBB, BB);
-    if (DominatingEdge.isSingleEdge()) {
-      // We're constructively (and conservatively) enumerating edges within the
-      // loop body that dominate the latch.  The dominator tree better agree
-      // with us on this:
-      assert(DT->dominates(DominatingEdge, Latch) && "should be!");
-
-      if (isImpliedCond(Pred, LHS, RHS, Condition,
-                        BB != ContinuePredicate->getSuccessor(0)))
-        return true;
-    }
-  }
-
   // Check conditions due to any @llvm.assume intrinsics.
   for (auto &AssumeVH : AC->assumptions()) {
     if (!AssumeVH)