[SCEV] Change the SCEV Predicates interfaces for conversion to AddRec…

…Expr to return SCEVAddRecExpr* instead of SCEV*

Summary:
This changes the conversion functions from SCEV * to SCEVAddRecExpr from
ScalarEvolution and PredicatedScalarEvolution to return a SCEVAddRecExpr*
instead of a SCEV* (which removes the need of most clients to do a
dyn_cast right after calling these functions).

We also don't add new predicates if the transformation was not successful.

This is not entirely a NFC (as it can theoretically remove some predicates
from LAA when we have an unknown dependece), but I couldn't find an obvious
regression test for it.

Reviewers: sanjoy

Subscribers: sanjoy, mzolotukhin, llvm-commits

Differential Revision: http://reviews.llvm.org/D18368

llvm-svn: 264161

llvm/include/llvm/Analysis/ScalarEvolution.h

@@ -1397,8 +1397,9 @@ namespace llvm {
                                       SCEVUnionPredicate &A);
     /// Tries to convert the \p S expression to an AddRec expression,
     /// adding additional predicates to \p Preds as required.
-    const SCEV *convertSCEVToAddRecWithPredicates(const SCEV *S, const Loop *L,
-                                                  SCEVUnionPredicate &Preds);
+    const SCEVAddRecExpr *
+    convertSCEVToAddRecWithPredicates(const SCEV *S, const Loop *L,
+                                      SCEVUnionPredicate &Preds);
 
   private:
     /// Compute the backedge taken count knowing the interval difference, the
@@ -1495,8 +1496,10 @@ namespace llvm {
     /// \brief Adds a new predicate.
     void addPredicate(const SCEVPredicate &Pred);
     /// \brief Attempts to produce an AddRecExpr for V by adding additional
-    /// SCEV predicates.
-    const SCEV *getAsAddRec(Value *V);
+    /// SCEV predicates. If we can't transform the expression into an
+    /// AddRecExpr we return nullptr and not add additional SCEV predicates
+    /// to the current context.
+    const SCEVAddRecExpr *getAsAddRec(Value *V);
     /// \brief Proves that V doesn't overflow by adding SCEV predicate.
     void setNoOverflow(Value *V, SCEVWrapPredicate::IncrementWrapFlags Flags);
     /// \brief Returns true if we've proved that V doesn't wrap by means of a

llvm/lib/Analysis/LoopAccessAnalysis.cpp

@@ -837,7 +837,7 @@ int llvm::isStridedPtr(PredicatedScalarEvolution &PSE, Value *Ptr,
 
   const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(PtrScev);
   if (Assume && !AR)
-    AR = dyn_cast<SCEVAddRecExpr>(PSE.getAsAddRec(Ptr));
+    AR = PSE.getAsAddRec(Ptr);
 
   if (!AR) {
     DEBUG(dbgs() << "LAA: Bad stride - Not an AddRecExpr pointer " << *Ptr

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -9908,10 +9908,20 @@ const SCEV *ScalarEvolution::rewriteUsingPredicate(const SCEV *S, const Loop *L,
   return SCEVPredicateRewriter::rewrite(S, L, *this, Preds, false);
 }
 
-const SCEV *
+const SCEVAddRecExpr *
 ScalarEvolution::convertSCEVToAddRecWithPredicates(const SCEV *S, const Loop *L,
                                                    SCEVUnionPredicate &Preds) {
-  return SCEVPredicateRewriter::rewrite(S, L, *this, Preds, true);
+  SCEVUnionPredicate TransformPreds;
+  S = SCEVPredicateRewriter::rewrite(S, L, *this, TransformPreds, true);
+  auto *AddRec = dyn_cast<SCEVAddRecExpr>(S);
+
+  if (!AddRec)
+    return nullptr;
+
+  // Since the transformation was successful, we can now transfer the SCEV
+  // predicates.
+  Preds.add(&TransformPreds);
+  return AddRec;
 }
 
 /// SCEV predicates
@@ -10126,9 +10136,13 @@ bool PredicatedScalarEvolution::hasNoOverflow(
   return Flags == SCEVWrapPredicate::IncrementAnyWrap;
 }
 
-const SCEV *PredicatedScalarEvolution::getAsAddRec(Value *V) {
+const SCEVAddRecExpr *PredicatedScalarEvolution::getAsAddRec(Value *V) {
   const SCEV *Expr = this->getSCEV(V);
-  const SCEV *New = SE.convertSCEVToAddRecWithPredicates(Expr, &L, Preds);
+  auto *New = SE.convertSCEVToAddRecWithPredicates(Expr, &L, Preds);
+
+  if (!New)
+    return nullptr;
+
   updateGeneration();
   RewriteMap[SE.getSCEV(V)] = {Generation, New};
   return New;