[APInt] Implement APInt::intersects without creating a temporary APInt in the multiword case

Summary: This is a simple question we should be able to answer without creating a temporary to hold the AND result. We can also get an early out as soon as we find a word that intersects.

Reviewers: RKSimon, hans, spatel, davide

Reviewed By: hans, davide

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32253

llvm-svn: 300812

llvm/include/llvm/ADT/APInt.h

@@ -209,6 +209,9 @@ private:
   /// out-of-line slow case for countPopulation
   unsigned countPopulationSlowCase() const LLVM_READONLY;
 
+  /// out-of-line slow case for intersects.
+  bool intersectsSlowCase(const APInt &RHS) const LLVM_READONLY;
+
   /// out-of-line slow case for setBits.
   void setBitsSlowCase(unsigned loBit, unsigned hiBit);
 
@@ -1206,9 +1209,10 @@ public:
   /// This operation tests if there are any pairs of corresponding bits
   /// between this APInt and RHS that are both set.
   bool intersects(const APInt &RHS) const {
-    APInt temp(*this);
-    temp &= RHS;
-    return temp != 0;
+    assert(BitWidth == RHS.BitWidth && "Bit widths must be the same");
+    if (isSingleWord())
+      return (VAL & RHS.VAL) != 0;
+    return intersectsSlowCase(RHS);
   }
 
   /// @}

llvm/lib/Support/APInt.cpp

@@ -722,6 +722,14 @@ unsigned APInt::countPopulationSlowCase() const {
   return Count;
 }
 
+bool APInt::intersectsSlowCase(const APInt &RHS) const {
+  for (unsigned i = 0, e = getNumWords(); i != e; ++i)
+    if ((pVal[i] & RHS.pVal[i]) != 0)
+      return true;
+
+  return false;
+}
+
 APInt APInt::byteSwap() const {
   assert(BitWidth >= 16 && BitWidth % 16 == 0 && "Cannot byteswap!");
   if (BitWidth == 16)