From 377b1190cbcf99e9298300d890c4b744dd2ed2c7 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Sat, 14 Jul 2007 02:51:34 +0000
Subject: [PATCH] Add alternate ConstantRange intersection algorithm.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@39851 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Support/ConstantRange.h |  6 +++
 lib/Support/ConstantRange.cpp        | 81 ++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)

diff --git a/include/llvm/Support/ConstantRange.h b/include/llvm/Support/ConstantRange.h
index 020fb095ec0..00c525ebf32 100644
--- a/include/llvm/Support/ConstantRange.h
+++ b/include/llvm/Support/ConstantRange.h
@@ -143,6 +143,12 @@ class ConstantRange {
   ///
   ConstantRange intersectWith(const ConstantRange &CR) const;
 
+  /// maximalIntersectWith - Return the range that results from the intersection
+  /// of this range with another range.  The resultant range is guaranteed to
+  /// include all elements contained in both input ranges, and is also
+  /// guaranteed to be the smallest possible set that does so.
+  ConstantRange maximalIntersectWith(const ConstantRange &CR) const;
+
   /// unionWith - Return the range that results from the union of this range
   /// with another range.  The resultant range is guaranteed to include the
   /// elements of both sets, but may contain more.  For example, [3, 9) union
diff --git a/lib/Support/ConstantRange.cpp b/lib/Support/ConstantRange.cpp
index 966de801be0..4f132e5ed5f 100644
--- a/lib/Support/ConstantRange.cpp
+++ b/lib/Support/ConstantRange.cpp
@@ -246,6 +246,87 @@ ConstantRange ConstantRange::intersectWith(const ConstantRange &CR) const {
   return *this;
 }
 
+/// maximalIntersectWith - Return the range that results from the intersection
+/// of this range with another range.  The resultant range is guaranteed to
+/// include all elements contained in both input ranges, and is also guaranteed
+/// to be the smallest possible set that does so.
+ConstantRange ConstantRange::maximalIntersectWith(const ConstantRange &CR) const {
+  assert(getBitWidth() == CR.getBitWidth() && 
+         "ConstantRange types don't agree!");
+
+  // Handle common cases.
+  if (   isEmptySet() || CR.isFullSet()) return *this;
+  if (CR.isEmptySet() ||    isFullSet()) return CR;
+
+  if (!isWrappedSet() && CR.isWrappedSet())
+    return CR.maximalIntersectWith(*this);
+
+  if (!isWrappedSet() && !CR.isWrappedSet()) {
+    if (Lower.ult(CR.Lower)) {
+      if (Upper.ule(CR.Lower))
+        return ConstantRange(getBitWidth(), false);
+
+      if (Upper.ult(CR.Upper))
+        return ConstantRange(CR.Lower, Upper);
+
+      return CR;
+    } else {
+      if (Upper.ult(CR.Upper))
+        return *this;
+
+      if (Lower.ult(CR.Upper))
+        return ConstantRange(Lower, CR.Upper);
+
+      return ConstantRange(getBitWidth(), false);
+    }
+  }
+
+  if (isWrappedSet() && !CR.isWrappedSet()) {
+    if (CR.Lower.ult(Upper)) {
+      if (CR.Upper.ult(Upper))
+        return CR;
+
+      if (CR.Upper.ult(Lower))
+        return ConstantRange(CR.Lower, Upper);
+
+      if (getSetSize().ult(CR.getSetSize()))
+        return *this;
+      else
+        return CR;
+    } else if (CR.Lower.ult(Lower)) {
+      if (CR.Upper.ule(Lower))
+        return ConstantRange(getBitWidth(), false);
+
+      return ConstantRange(Lower, CR.Upper);
+    }
+    return CR;
+  }
+
+  if (CR.Upper.ult(Upper)) {
+    if (CR.Lower.ult(Upper)) {
+      if (getSetSize().ult(CR.getSetSize()))
+        return *this;
+      else
+        return CR;
+    }
+
+    if (CR.Lower.ult(Lower))
+      return ConstantRange(Lower, CR.Upper);
+
+    return CR;
+  } else if (CR.Upper.ult(Lower)) {
+    if (CR.Lower.ult(Lower))
+      return *this;
+
+    return ConstantRange(CR.Lower, Upper);
+  }
+  if (getSetSize().ult(CR.getSetSize()))
+    return *this;
+  else
+    return CR;
+}
+
+
 /// unionWith - Return the range that results from the union of this range with
 /// another range.  The resultant range is guaranteed to include the elements of
 /// both sets, but may contain more.  For example, [3, 9) union [12,15) is
-- 
2.34.1