implement shl, ashr, and lshr methods. shl is not fully implemented as it is quite tricky.

llvm-svn: 86986

llvm/include/llvm/Support/ConstantRange.h

@@ -217,6 +217,18 @@ public:
   /// TODO: This isn't fully implemented yet.
   ConstantRange udiv(const ConstantRange &Other) const;
 
+  /// shl - Return a new range representing the possible values resulting
+  /// from a left shift of a value in this range by the Amount value.
+  ConstantRange shl(const ConstantRange &Amount) const;
+
+  /// ashr - Return a new range representing the possible values resulting from
+  /// an arithmetic right shift of a value in this range by the Amount value.
+  ConstantRange ashr(const ConstantRange &Amount) const;
+
+  /// shr - Return a new range representing the possible values resulting
+  /// from a logical right shift of a value in this range by the Amount value.
+  ConstantRange lshr(const ConstantRange &Amount) const;
+
   /// print - Print out the bounds to a stream...
   ///
   void print(raw_ostream &OS) const;

llvm/lib/Support/ConstantRange.cpp

@@ -609,6 +609,43 @@ ConstantRange::udiv(const ConstantRange &RHS) const {
   return ConstantRange(Lower, Upper);
 }
 
+ConstantRange
+ConstantRange::shl(const ConstantRange &Amount) const {
+  if (isEmptySet())
+    return *this;
+
+  APInt min = getUnsignedMin() << Amount.getUnsignedMin();
+  APInt max = getUnsignedMax() << Amount.getUnsignedMax();
+
+  // there's no overflow!
+  APInt Zeros(sizeof(unsigned)*8, getUnsignedMax().countLeadingZeros());
+  if (Zeros.uge(Amount.getUnsignedMax()))
+    return ConstantRange(min, max);
+
+  // FIXME: implement the other tricky cases
+  return ConstantRange(getBitWidth());
+}
+
+ConstantRange
+ConstantRange::ashr(const ConstantRange &Amount) const {
+  if (isEmptySet())
+    return *this;
+
+  APInt min = getUnsignedMax().ashr(Amount.getUnsignedMin());
+  APInt max = getUnsignedMin().ashr(Amount.getUnsignedMax());
+  return ConstantRange(min, max);
+}
+
+ConstantRange
+ConstantRange::lshr(const ConstantRange &Amount) const {
+  if (isEmptySet())
+    return *this;
+  
+  APInt min = getUnsignedMax().lshr(Amount.getUnsignedMin());
+  APInt max = getUnsignedMin().lshr(Amount.getUnsignedMax());
+  return ConstantRange(min, max);
+}
+
 /// print - Print out the bounds to a stream...
 ///
 void ConstantRange::print(raw_ostream &OS) const {