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

[craig.topper]

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.

[hans]

lgtm!

[davide]

lib/Support/APInt.cpp

727–728

Shouldn't just pVal[i] & RHS.pVal[i] suffice?

Then at that point you can just rewrite it as :
return llvm::all_of etc..

[davide]

lib/Support/APInt.cpp

727–728

Nevermind, you probably can't use any_of as you need the index.

include/llvm/ADT/APInt.h

private:
   unsigned countLeadingZerosSlowCase() const LLVM_READONLY;
 
   /// out-of-line slow case for countTrailingOnes
   unsigned countTrailingOnesSlowCase() const LLVM_READONLY;
 
   /// 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);
 
   /// out-of-line slow case for flipAllBits.
   void flipAllBitsSlowCase();
 
   /// out-of-line slow case for operator&=.
   void AndAssignSlowCase(const APInt& RHS);
public:
   /// the validity of the greater-or-equal relationship.
   ///
   /// \returns true if *this >= RHS when considered signed.
   bool sge(int64_t RHS) const { return !slt(RHS); }
 
   /// 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);
   }
 
   /// @}
   /// \name Resizing Operators
   /// @{
 
   /// \brief Truncate to new width.
   ///

lib/Support/APInt.cpp

 
 unsigned APInt::countPopulationSlowCase() const {
   unsigned Count = 0;
   for (unsigned i = 0; i < getNumWords(); ++i)
     Count += llvm::countPopulation(pVal[i]);
   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)
     return APInt(BitWidth, ByteSwap_16(uint16_t(VAL)));
   if (BitWidth == 32)
     return APInt(BitWidth, ByteSwap_32(unsigned(VAL)));
   if (BitWidth == 48) {
     unsigned Tmp1 = unsigned(VAL >> 16);