Revert "[SCEVExpander] Remove GEP add rec splitting code (NFCI)"

This reverts commit b752542.

Author: Chenyang-L

llvm/include/llvm/Transforms/Utils/ScalarEvolutionExpander.h

@@ -440,6 +440,8 @@ class SCEVExpander : public SCEVVisitor<SCEVExpander, Value *> {
 
   /// Expand a SCEVAddExpr with a pointer type into a GEP instead of using
   /// ptrtoint+arithmetic+inttoptr.
+  Value *expandAddToGEP(const SCEV *const *op_begin, const SCEV *const *op_end,
+                        Type *Ty, Value *V);
   Value *expandAddToGEP(const SCEV *Op, Type *Ty, Value *V);
 
   /// Find a previous Value in ExprValueMap for expand.

llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp

@@ -286,6 +286,69 @@ Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode,
   return BO;
 }
 
+/// SimplifyAddOperands - Sort and simplify a list of add operands. NumAddRecs
+/// is the number of SCEVAddRecExprs present, which are kept at the end of
+/// the list.
+///
+static void SimplifyAddOperands(SmallVectorImpl<const SCEV *> &Ops,
+                                Type *Ty,
+                                ScalarEvolution &SE) {
+  unsigned NumAddRecs = 0;
+  for (unsigned i = Ops.size(); i > 0 && isa<SCEVAddRecExpr>(Ops[i-1]); --i)
+    ++NumAddRecs;
+  // Group Ops into non-addrecs and addrecs.
+  SmallVector<const SCEV *, 8> NoAddRecs(Ops.begin(), Ops.end() - NumAddRecs);
+  SmallVector<const SCEV *, 8> AddRecs(Ops.end() - NumAddRecs, Ops.end());
+  // Let ScalarEvolution sort and simplify the non-addrecs list.
+  const SCEV *Sum = NoAddRecs.empty() ?
+                    SE.getConstant(Ty, 0) :
+                    SE.getAddExpr(NoAddRecs);
+  // If it returned an add, use the operands. Otherwise it simplified
+  // the sum into a single value, so just use that.
+  Ops.clear();
+  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Sum))
+    append_range(Ops, Add->operands());
+  else if (!Sum->isZero())
+    Ops.push_back(Sum);
+  // Then append the addrecs.
+  Ops.append(AddRecs.begin(), AddRecs.end());
+}
+
+/// SplitAddRecs - Flatten a list of add operands, moving addrec start values
+/// out to the top level. For example, convert {a + b,+,c} to a, b, {0,+,d}.
+/// This helps expose more opportunities for folding parts of the expressions
+/// into GEP indices.
+///
+static void SplitAddRecs(SmallVectorImpl<const SCEV *> &Ops,
+                         Type *Ty,
+                         ScalarEvolution &SE) {
+  // Find the addrecs.
+  SmallVector<const SCEV *, 8> AddRecs;
+  for (unsigned i = 0, e = Ops.size(); i != e; ++i)
+    while (const SCEVAddRecExpr *A = dyn_cast<SCEVAddRecExpr>(Ops[i])) {
+      const SCEV *Start = A->getStart();
+      if (Start->isZero()) break;
+      const SCEV *Zero = SE.getConstant(Ty, 0);
+      AddRecs.push_back(SE.getAddRecExpr(Zero,
+                                         A->getStepRecurrence(SE),
+                                         A->getLoop(),
+                                         A->getNoWrapFlags(SCEV::FlagNW)));
+      if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Start)) {
+        Ops[i] = Zero;
+        append_range(Ops, Add->operands());
+        e += Add->getNumOperands();
+      } else {
+        Ops[i] = Start;
+      }
+    }
+  if (!AddRecs.empty()) {
+    // Add the addrecs onto the end of the list.
+    Ops.append(AddRecs.begin(), AddRecs.end());
+    // Resort the operand list, moving any constants to the front.
+    SimplifyAddOperands(Ops, Ty, SE);
+  }
+}
+
 /// expandAddToGEP - Expand an addition expression with a pointer type into
 /// a GEP instead of using ptrtoint+arithmetic+inttoptr. This helps
 /// BasicAliasAnalysis and other passes analyze the result. See the rules
@@ -313,11 +376,20 @@ Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode,
 /// loop-invariant portions of expressions, after considering what
 /// can be folded using target addressing modes.
 ///
-Value *SCEVExpander::expandAddToGEP(const SCEV *Offset, Type *Ty, Value *V) {
+Value *SCEVExpander::expandAddToGEP(const SCEV *const *op_begin,
+                                    const SCEV *const *op_end, Type *Ty,
+                                    Value *V) {
+  SmallVector<const SCEV *, 8> Ops(op_begin, op_end);
+
+  // Split AddRecs up into parts as either of the parts may be usable
+  // without the other.
+  SplitAddRecs(Ops, Ty, SE);
+
   assert(!isa<Instruction>(V) ||
          SE.DT.dominates(cast<Instruction>(V), &*Builder.GetInsertPoint()));
 
-  Value *Idx = expandCodeForImpl(Offset, Ty);
+  // Expand the operands for a plain byte offset.
+  Value *Idx = expandCodeForImpl(SE.getAddExpr(Ops), Ty);
 
   // Fold a GEP with constant operands.
   if (Constant *CLHS = dyn_cast<Constant>(V))
@@ -362,6 +434,11 @@ Value *SCEVExpander::expandAddToGEP(const SCEV *Offset, Type *Ty, Value *V) {
   return Builder.CreateGEP(Builder.getInt8Ty(), V, Idx, "scevgep");
 }
 
+Value *SCEVExpander::expandAddToGEP(const SCEV *Op, Type *Ty, Value *V) {
+  const SCEV *const Ops[1] = {Op};
+  return expandAddToGEP(Ops, Ops + 1, Ty, V);
+}
+
 /// PickMostRelevantLoop - Given two loops pick the one that's most relevant for
 /// SCEV expansion. If they are nested, this is the most nested. If they are
 /// neighboring, pick the later.
@@ -498,7 +575,7 @@ Value *SCEVExpander::visitAddExpr(const SCEVAddExpr *S) {
             X = SE.getSCEV(U->getValue());
         NewOps.push_back(X);
       }
-      Sum = expandAddToGEP(SE.getAddExpr(NewOps), Ty, Sum);
+      Sum = expandAddToGEP(NewOps.begin(), NewOps.end(), Ty, Sum);
     } else if (Op->isNonConstantNegative()) {
       // Instead of doing a negate and add, just do a subtract.
       Value *W = expandCodeForImpl(SE.getNegativeSCEV(Op), Ty);