[ConstantRange] binaryXor(): special-case binary complement case - the result is precise

Use the fact that `~X` is equivalent to `-1 - X`, which gives us
fully-precise answer, and we only need to special-handle the wrapped case.

This fires ~16k times for vanilla llvm test-suite + RawSpeed.

1 files changed, 16 insertions, 0 deletions

diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index 396c39b..7b8dd66 100644
--- a/llvm/lib/IR/ConstantRange.cpp
+++ b/llvm/lib/IR/ConstantRange.cpp
@@ -1240,6 +1240,16 @@ ConstantRange ConstantRange::srem(const ConstantRange &RHS) const {
   return ConstantRange(std::move(Lower), std::move(Upper));
 }
 
+ConstantRange ConstantRange::binaryNot() const {
+  if (isEmptySet())
+    return getEmpty();
+
+  if (isWrappedSet())
+    return getFull();
+
+  return ConstantRange(APInt::getAllOnesValue(getBitWidth())).sub(*this);
+}
+
 ConstantRange
 ConstantRange::binaryAnd(const ConstantRange &Other) const {
   if (isEmptySet() || Other.isEmptySet())
@@ -1278,6 +1288,12 @@ ConstantRange ConstantRange::binaryXor(const ConstantRange &Other) const {
   if (isSingleElement() && Other.isSingleElement())
     return {*getSingleElement() ^ *Other.getSingleElement()};
 
+  // Special-case binary complement, since we can give a precise answer.
+  if (Other.isSingleElement() && Other.getSingleElement()->isAllOnesValue())
+    return binaryNot();
+  if (isSingleElement() && getSingleElement()->isAllOnesValue())
+    return Other.binaryNot();
+
   // TODO: replace this with something less conservative
   return getFull();
 }