[ValueTracking] computeOverflowForSignedAdd and isKnownNonNegative

Summary:
Refactor, NFC

Extracts computeOverflowForSignedAdd and isKnownNonNegative from NaryReassociate to ValueTracking in case
others need it.

Reviewers: reames

Subscribers: majnemer, llvm-commits

Differential Revision: http://reviews.llvm.org/D11313

llvm-svn: 245591

1 files changed, 6 insertions, 29 deletions

diff --git a/llvm/lib/Transforms/Scalar/NaryReassociate.cpp b/llvm/lib/Transforms/Scalar/NaryReassociate.cpp
index aae1cce..4640168 100644
--- a/llvm/lib/Transforms/Scalar/NaryReassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/NaryReassociate.cpp
@@ -161,11 +161,6 @@ private:
   // GEP's pointer size, i.e., whether Index needs to be sign-extended in order
   // to be an index of GEP.
   bool requiresSignExtension(Value *Index, GetElementPtrInst *GEP);
-  // Returns whether V is known to be non-negative at context \c Ctxt.
-  bool isKnownNonNegative(Value *V, Instruction *Ctxt);
-  // Returns whether AO may sign overflow at context \c Ctxt. It computes a
-  // conservative result -- it answers true when not sure.
-  bool maySignOverflow(AddOperator *AO, Instruction *Ctxt);
 
   AssumptionCache *AC;
   const DataLayout *DL;
@@ -352,27 +347,6 @@ bool NaryReassociate::requiresSignExtension(Value *Index,
   return cast<IntegerType>(Index->getType())->getBitWidth() < PointerSizeInBits;
 }
 
-bool NaryReassociate::isKnownNonNegative(Value *V, Instruction *Ctxt) {
-  bool NonNegative, Negative;
-  // TODO: ComputeSignBits is expensive. Consider caching the results.
-  ComputeSignBit(V, NonNegative, Negative, *DL, 0, AC, Ctxt, DT);
-  return NonNegative;
-}
-
-bool NaryReassociate::maySignOverflow(AddOperator *AO, Instruction *Ctxt) {
-  if (AO->hasNoSignedWrap())
-    return false;
-
-  Value *LHS = AO->getOperand(0), *RHS = AO->getOperand(1);
-  // If LHS or RHS has the same sign as the sum, AO doesn't sign overflow.
-  // TODO: handle the negative case as well.
-  if (isKnownNonNegative(AO, Ctxt) &&
-      (isKnownNonNegative(LHS, Ctxt) || isKnownNonNegative(RHS, Ctxt)))
-    return false;
-
-  return true;
-}
-
 GetElementPtrInst *
 NaryReassociate::tryReassociateGEPAtIndex(GetElementPtrInst *GEP, unsigned I,
                                           Type *IndexedType) {
@@ -381,7 +355,7 @@ NaryReassociate::tryReassociateGEPAtIndex(GetElementPtrInst *GEP, unsigned I,
     IndexToSplit = SExt->getOperand(0);
   } else if (ZExtInst *ZExt = dyn_cast<ZExtInst>(IndexToSplit)) {
     // zext can be treated as sext if the source is non-negative.
-    if (isKnownNonNegative(ZExt->getOperand(0), GEP))
+    if (isKnownNonNegative(ZExt->getOperand(0), *DL, 0, AC, GEP, DT))
       IndexToSplit = ZExt->getOperand(0);
   }
 
@@ -389,8 +363,11 @@ NaryReassociate::tryReassociateGEPAtIndex(GetElementPtrInst *GEP, unsigned I,
     // If the I-th index needs sext and the underlying add is not equipped with
     // nsw, we cannot split the add because
     //   sext(LHS + RHS) != sext(LHS) + sext(RHS).
-    if (requiresSignExtension(IndexToSplit, GEP) && maySignOverflow(AO, GEP))
+    if (requiresSignExtension(IndexToSplit, GEP) &&
+        computeOverflowForSignedAdd(AO, *DL, AC, GEP, DT) !=
+            OverflowResult::NeverOverflows)
       return nullptr;
+
     Value *LHS = AO->getOperand(0), *RHS = AO->getOperand(1);
     // IndexToSplit = LHS + RHS.
     if (auto *NewGEP = tryReassociateGEPAtIndex(GEP, I, LHS, RHS, IndexedType))
@@ -415,7 +392,7 @@ GetElementPtrInst *NaryReassociate::tryReassociateGEPAtIndex(
     IndexExprs.push_back(SE->getSCEV(*Index));
   // Replace the I-th index with LHS.
   IndexExprs[I] = SE->getSCEV(LHS);
-  if (isKnownNonNegative(LHS, GEP) &&
+  if (isKnownNonNegative(LHS, *DL, 0, AC, GEP, DT) &&
       DL->getTypeSizeInBits(LHS->getType()) <
           DL->getTypeSizeInBits(GEP->getOperand(I)->getType())) {
     // Zero-extend LHS if it is non-negative. InstCombine canonicalizes sext to