Add a new isSignWrappedSet() method to ConstantRange.

Fix zeroExtend and signExtend to support empty sets, and to return the smallest
possible result set which contains the extension of each element in their
inputs. For example zext i8 [100, 10) to i16 is now [0, 256), not i16 [100, 10)
which contains 63446 members.

llvm-svn: 113187

1 files changed, 15 insertions, 3 deletions

diff --git a/llvm/lib/Support/ConstantRange.cpp b/llvm/lib/Support/ConstantRange.cpp
index 8ef3785f533..defb8189b62 100644
--- a/llvm/lib/Support/ConstantRange.cpp
+++ b/llvm/lib/Support/ConstantRange.cpp
@@ -115,6 +115,14 @@ bool ConstantRange::isWrappedSet() const {
   return Lower.ugt(Upper);
 }
 
+/// isSignWrappedSet - Return true if this set wraps around the INT_MIN of
+/// its bitwidth, for example: i8 [120, 140).
+///
+bool ConstantRange::isSignWrappedSet() const {
+  return contains(APInt::getSignedMaxValue(getBitWidth())) &&
+         contains(APInt::getSignedMinValue(getBitWidth()));
+}
+
 /// getSetSize - Return the number of elements in this set.
 ///
 APInt ConstantRange::getSetSize() const {
@@ -408,10 +416,12 @@ ConstantRange ConstantRange::unionWith(const ConstantRange &CR) const {
 /// correspond to the possible range of values as if the source range had been
 /// zero extended.
 ConstantRange ConstantRange::zeroExtend(uint32_t DstTySize) const {
+  if (isEmptySet()) return ConstantRange(DstTySize, /*isFullSet=*/false);
+
   unsigned SrcTySize = getBitWidth();
   assert(SrcTySize < DstTySize && "Not a value extension");
-  if (isFullSet())
-    // Change a source full set into [0, 1 << 8*numbytes)
+  if (isFullSet() || isWrappedSet())
+    // Change into [0, 1 << src bit width)
     return ConstantRange(APInt(DstTySize,0), APInt(DstTySize,1).shl(SrcTySize));
 
   APInt L = Lower; L.zext(DstTySize);
@@ -424,9 +434,11 @@ ConstantRange ConstantRange::zeroExtend(uint32_t DstTySize) const {
 /// correspond to the possible range of values as if the source range had been
 /// sign extended.
 ConstantRange ConstantRange::signExtend(uint32_t DstTySize) const {
+  if (isEmptySet()) return ConstantRange(DstTySize, /*isFullSet=*/false);
+
   unsigned SrcTySize = getBitWidth();
   assert(SrcTySize < DstTySize && "Not a value extension");
-  if (isFullSet()) {
+  if (isFullSet() || isSignWrappedSet()) {
     return ConstantRange(APInt::getHighBitsSet(DstTySize,DstTySize-SrcTySize+1),
                          APInt::getLowBitsSet(DstTySize, SrcTySize-1) + 1);
   }