[NFC] Move functon from IndVarSimplify to SCEV

[mkazantsev]

Summary

This function can be reused in other places.

[lebedev.ri]

This seems pretty NFC-ish, not sure why it would require review.
SGTM

[fhahn]

LGTM, thanks!

[mkazantsev]

In D87274#2260451, @lebedev.ri wrote:

This seems pretty NFC-ish, not sure why it would require review.
SGTM

Because of renaming, mostly. :)

llvm/include/llvm/Analysis/ScalarEvolution.h

public:
   /// When successful, this returns a SCEVConstant that is greater than or equal
   /// to (i.e. a "conservative over-approximation") of the value returend by
   /// getBackedgeTakenCount.  If such a value cannot be computed, it returns the
   /// SCEVCouldNotCompute object.
   const SCEV *getConstantMaxBackedgeTakenCount(const Loop *L) {
     return getBackedgeTakenCount(L, ConstantMaximum);
   } 
 
+  /// Return a symbolic upper bound for the backedge taken count of the loop.
+  /// This is more general than getConstantMaxBackedgeTakenCount as it returns
+  /// an arbitrary expression as opposed to only constants.
+  const SCEV* computeMaxBackedgeTakenCount(const Loop *L);
+
   /// Return true if the backedge taken count is either the value returned by
   /// getConstantMaxBackedgeTakenCount or zero.
   bool isBackedgeTakenCountMaxOrZero(const Loop *L);
 
   /// Return true if the specified loop has an analyzable loop-invariant
   /// backedge-taken count.
   bool hasLoopInvariantBackedgeTakenCount(const Loop *L);
 

llvm/lib/Analysis/ScalarEvolution.cpp

bool ScalarEvolution::matchURem(const SCEV *Expr, const SCEV *&LHS,
   // (SomeExpr + ((-SomeExpr / B) * B)) or (SomeExpr + ((SomeExpr / B) * -B)).
   if (Mul->getNumOperands() == 2)
     return MatchURemWithDivisor(Mul->getOperand(1)) ||
            MatchURemWithDivisor(Mul->getOperand(0)) ||
            MatchURemWithDivisor(getNegativeSCEV(Mul->getOperand(1))) ||
            MatchURemWithDivisor(getNegativeSCEV(Mul->getOperand(0)));
   return false;
 }
+
+const SCEV* ScalarEvolution::computeMaxBackedgeTakenCount(const Loop *L) {
+  SmallVector<BasicBlock*, 16> ExitingBlocks;
+  L->getExitingBlocks(ExitingBlocks);
+
+  // Form an expression for the maximum exit count possible for this loop. We
+  // merge the max and exact information to approximate a version of
+  // getConstantMaxBackedgeTakenCount which isn't restricted to just constants.
+  SmallVector<const SCEV*, 4> ExitCounts;
+  for (BasicBlock *ExitingBB : ExitingBlocks) {
+    const SCEV *ExitCount = getExitCount(L, ExitingBB);
+    if (isa<SCEVCouldNotCompute>(ExitCount))
+      ExitCount = getExitCount(L, ExitingBB,
+                                  ScalarEvolution::ConstantMaximum);
+    if (!isa<SCEVCouldNotCompute>(ExitCount)) {
+      assert(DT.dominates(ExitingBB, L->getLoopLatch()) &&
+             "We should only have known counts for exiting blocks that "
+             "dominate latch!");
+      ExitCounts.push_back(ExitCount);
+    }
+  }
+  if (ExitCounts.empty())
+    return getCouldNotCompute();
+  return getUMinFromMismatchedTypes(ExitCounts);
+}

llvm/lib/Transforms/Scalar/IndVarSimplify.cpp

while (I != Preheader->begin()) {
     ToMove->moveBefore(*ExitBlock, InsertPt);
     if (Done) break;
     InsertPt = ToMove->getIterator();
   }
 
   return MadeAnyChanges;
 }
 
-/// Return a symbolic upper bound for the backedge taken count of the loop.
-/// This is more general than getConstantMaxBackedgeTakenCount as it returns
-/// an arbitrary expression as opposed to only constants.
-/// TODO: Move into the ScalarEvolution class.
-static const SCEV* getMaxBackedgeTakenCount(ScalarEvolution &SE,
-                                            DominatorTree &DT, Loop *L) {
-  SmallVector<BasicBlock*, 16> ExitingBlocks;
-  L->getExitingBlocks(ExitingBlocks);
-
-  // Form an expression for the maximum exit count possible for this loop. We
-  // merge the max and exact information to approximate a version of
-  // getConstantMaxBackedgeTakenCount which isn't restricted to just constants.
-  SmallVector<const SCEV*, 4> ExitCounts;
-  for (BasicBlock *ExitingBB : ExitingBlocks) {
-    const SCEV *ExitCount = SE.getExitCount(L, ExitingBB);
-    if (isa<SCEVCouldNotCompute>(ExitCount))
-      ExitCount = SE.getExitCount(L, ExitingBB,
-                                  ScalarEvolution::ConstantMaximum);
-    if (!isa<SCEVCouldNotCompute>(ExitCount)) {
-      assert(DT.dominates(ExitingBB, L->getLoopLatch()) &&
-             "We should only have known counts for exiting blocks that "
-             "dominate latch!");
-      ExitCounts.push_back(ExitCount);
-    }
-  }
-  if (ExitCounts.empty())
-    return SE.getCouldNotCompute();
-  return SE.getUMinFromMismatchedTypes(ExitCounts);
-}
-
 bool IndVarSimplify::optimizeLoopExits(Loop *L, SCEVExpander &Rewriter) {
   SmallVector<BasicBlock*, 16> ExitingBlocks;
   L->getExitingBlocks(ExitingBlocks);
 
   // Remove all exits which aren't both rewriteable and analyzeable.
   auto NewEnd = llvm::remove_if(ExitingBlocks, [&](BasicBlock *ExitingBB) {
     // If our exitting block exits multiple loops, we can only rewrite the
     // innermost one.  Otherwise, we're changing how many times the innermost
auto NewEnd = llvm::remove_if(ExitingBlocks, [&](BasicBlock *ExitingBB) {
     return false;
   });
   ExitingBlocks.erase(NewEnd, ExitingBlocks.end());
 
   if (ExitingBlocks.empty())
     return false;
 
   // Get a symbolic upper bound on the loop backedge taken count.
-  const SCEV *MaxExitCount = getMaxBackedgeTakenCount(*SE, *DT, L);
+  const SCEV *MaxExitCount = SE->computeMaxBackedgeTakenCount(L);
   if (isa<SCEVCouldNotCompute>(MaxExitCount))
     return false;
 
   // Visit our exit blocks in order of dominance.  We know from the fact that
   // all exits (left) are analyzeable that the must be a total dominance order
   // between them as each must dominate the latch.  The visit order only
   // matters for the provably equal case.
   llvm::sort(ExitingBlocks,