Revert "[ScalarEvolution] Handling for ICmp occuring in the evolution chain."

This reverts commit r316054.  There was some confusion over the review process:
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20171016/495884.html

llvm-svn: 316129

llvm/include/llvm/Analysis/ScalarEvolution.h

@@ -1378,9 +1378,6 @@ private:
   /// Helper function called from createNodeForPHI.
   const SCEV *createAddRecFromPHI(PHINode *PN);
 
-  /// Evaluate ICmpInst to a constant node for special patterns.
-  const SCEV *evaluateForICmp(ICmpInst *IC);
-
   /// A helper function for createAddRecFromPHI to handle simple cases.
   const SCEV *createSimpleAffineAddRec(PHINode *PN, Value *BEValueV,
                                             Value *StartValueV);

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -4756,25 +4756,10 @@ const SCEV *ScalarEvolution::createAddRecFromPHI(PHINode *PN) {
           Ops.push_back(Add->getOperand(i));
       const SCEV *Accum = getAddExpr(Ops);
 
-      bool InvariantF = isLoopInvariant(Accum, L);
-
-      if (!InvariantF && Accum->getSCEVType() == scZeroExtend) {
-        const SCEV *Op = dyn_cast<SCEVZeroExtendExpr>(Accum)->getOperand();
-        const SCEVUnknown *Un = dyn_cast<SCEVUnknown>(Op);
-        if (Un && Un->getValue() && isa<Instruction>(Un->getValue()) &&
-            dyn_cast<Instruction>(Un->getValue())->getOpcode() ==
-                Instruction::ICmp) {
-          const SCEV *ICmpSC = evaluateForICmp(cast<ICmpInst>(Un->getValue()));
-          bool IsConstSC = ICmpSC->getSCEVType() == scConstant;
-          Accum =
-              IsConstSC ? getZeroExtendExpr(ICmpSC, Accum->getType()) : Accum;
-          InvariantF = IsConstSC ? true : false;
-        }
-      }
-
       // This is not a valid addrec if the step amount is varying each
       // loop iteration, but is not itself an addrec in this loop.
-      if (InvariantF || (isa<SCEVAddRecExpr>(Accum) &&
+      if (isLoopInvariant(Accum, L) ||
+          (isa<SCEVAddRecExpr>(Accum) &&
            cast<SCEVAddRecExpr>(Accum)->getLoop() == L)) {
         SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap;
 
@@ -6458,30 +6443,6 @@ void ScalarEvolution::forgetLoop(const Loop *L) {
   }
 }
 
-
-const SCEV *ScalarEvolution::evaluateForICmp(ICmpInst *IC) {
-  BasicBlock *Latch = nullptr;
-  const Loop *L = LI.getLoopFor(IC->getParent());
-
-  // If compare instruction is same or inverse of the compare in the
-  // branch of the loop latch, then return a constant evolution
-  // node. This shall facilitate computations of loop exit counts
-  // in cases where compare appears in the evolution chain of induction
-  // variables.
-  if (L && (Latch = L->getLoopLatch())) {
-    BranchInst *BI = dyn_cast<BranchInst>(Latch->getTerminator());
-    if (BI && BI->isConditional() && BI->getCondition() == IC) {
-      if (BI->getSuccessor(0) != L->getHeader())
-        return getZero(Type::getInt1Ty(getContext()));
-      else
-        return getOne(Type::getInt1Ty(getContext()));
-    }
-  }
-
-  return getUnknown(IC);
-}
-
-
 void ScalarEvolution::forgetValue(Value *V) {
   Instruction *I = dyn_cast<Instruction>(V);
   if (!I) return;

llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp

@@ -2969,11 +2969,8 @@ void LSRInstance::CollectChains() {
       // Ignore users that are part of a SCEV expression. This way we only
       // consider leaf IV Users. This effectively rediscovers a portion of
       // IVUsers analysis but in program order this time.
-      if (SE.isSCEVable(I.getType())) {
+      if (SE.isSCEVable(I.getType()) && !isa<SCEVUnknown>(SE.getSCEV(&I)))
-        const SCEV *SI = SE.getSCEV(&I);
-        if (!isa<SCEVUnknown>(SI) && !isa<SCEVConstant>(SI))
         continue;
-      }
 
       // Remove this instruction from any NearUsers set it may be in.
       for (unsigned ChainIdx = 0, NChains = IVChainVec.size();

llvm/test/Analysis/ScalarEvolution/pr34538.ll

@@ -1,19 +0,0 @@
-; RUN: opt -S -scalar-evolution -loop-deletion -simplifycfg -analyze < %s | FileCheck %s --check-prefix=CHECK-ANALYSIS
-
-define i32 @foo() local_unnamed_addr #0 {
-; CHECK-ANALYSIS: Loop %do.body: backedge-taken count is 10000
-; CHECK-ANALYSIS: Loop %do.body: max backedge-taken count is 10000
-; CHECK-ANALYSIS: Loop %do.body: Predicated backedge-taken count is 10000
-entry:
-  br label %do.body
-
-do.body:                                          ; preds = %do.body, %entry
-  %start.0 = phi i32 [ 0, %entry ], [ %inc.start.0, %do.body ]
-  %cmp = icmp slt i32 %start.0, 10000
-  %inc = zext i1 %cmp to i32
-  %inc.start.0 = add nsw i32 %start.0, %inc
-  br i1 %cmp, label %do.body, label %do.end
-
-do.end:                                           ; preds = %do.body
-  ret i32 0
-}