[PATCH] D12008: [ScalarEvolutionExpander] Refactor isHighCostExpansionHelper division case

[Igor Laevsky via llvm-commits]

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This is follow up after http://reviews.llvm.org/D11687

In `SCEVUDivExpr` case inside `isHighCostExpansionHelper` we had lookup code which was almost exactly same as code inside `findExistingExpansion`. Refactor it to make use of the existing function.

Repository:
  rL LLVM

http://reviews.llvm.org/D12008

Files:
  lib/Analysis/ScalarEvolutionExpander.cpp

Index: lib/Analysis/ScalarEvolutionExpander.cpp
===================================================================
--- lib/Analysis/ScalarEvolutionExpander.cpp
+++ lib/Analysis/ScalarEvolutionExpander.cpp
@@ -1816,11 +1816,11 @@
                                            const Instruction *At, Loop *L) {
   using namespace llvm::PatternMatch;
 
-  SmallVector<BasicBlock *, 4> Latches;
-  L->getLoopLatches(Latches);
+  SmallVector<BasicBlock *, 4> ExitingBlocks;
+  L->getExitingBlocks(ExitingBlocks);
 
-  // Look for suitable value in simple conditions at the loop latches.
-  for (BasicBlock *BB : Latches) {
+  // Look for suitable value in simple conditions at the loop exits.
+  for (BasicBlock *BB : ExitingBlocks) {
     ICmpInst::Predicate Pred;
     Instruction *LHS, *RHS;
     BasicBlock *TrueBB, *FalseBB;
@@ -1887,28 +1887,20 @@
     // UDivExpr is very likely a UDiv that ScalarEvolution's HowFarToZero or
     // HowManyLessThans produced to compute a precise expression, rather than a
     // UDiv from the user's code. If we can't find a UDiv in the code with some
-    // simple searching, assume the former consider UDivExpr expensive to
+    // simple searaching, assume the former consider UDivExpr expensive to
     // compute.
     BasicBlock *ExitingBB = L->getExitingBlock();
     if (!ExitingBB)
       return true;
 
-    BranchInst *ExitingBI = dyn_cast<BranchInst>(ExitingBB->getTerminator());
-    if (!ExitingBI || !ExitingBI->isConditional())
+    // We already tried to find existing value for plain 'S' at the beginning of
+    // this function. Now try to lookup 'S + 1' as it is common pattern
+    // involving division. This is just simple search heuristic.
+    if (!At)
+      At = &ExitingBB->back();
+    if (!findExistingExpansion(
+            SE.getAddExpr(S, SE.getConstant(S->getType(), 1)), At, L))
       return true;
-
-    ICmpInst *OrigCond = dyn_cast<ICmpInst>(ExitingBI->getCondition());
-    if (!OrigCond)
-      return true;
-
-    const SCEV *RHS = SE.getSCEV(OrigCond->getOperand(1));
-    RHS = SE.getMinusSCEV(RHS, SE.getConstant(RHS->getType(), 1));
-    if (RHS != S) {
-      const SCEV *LHS = SE.getSCEV(OrigCond->getOperand(0));
-      LHS = SE.getMinusSCEV(LHS, SE.getConstant(LHS->getType(), 1));
-      if (LHS != S)
-        return true;
-    }
   }
 
   // HowManyLessThans uses a Max expression whenever the loop is not guarded by


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