From b38d897e802664034c7e6e4654328256ed370a61 Mon Sep 17 00:00:00 2001
From: Roman Lebedev <lebedev.ri@gmail.com>
Date: Tue, 22 Sep 2020 11:50:25 +0300
Subject: [PATCH] [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.
---
 llvm/include/llvm/IR/ConstantRange.h    |  5 +++++
 llvm/lib/IR/ConstantRange.cpp           | 16 ++++++++++++++++
 llvm/unittests/IR/ConstantRangeTest.cpp | 18 ++++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/llvm/include/llvm/IR/ConstantRange.h b/llvm/include/llvm/IR/ConstantRange.h
index 318532b24e83..494a14a10cdb 100644
--- a/llvm/include/llvm/IR/ConstantRange.h
+++ b/llvm/include/llvm/IR/ConstantRange.h
@@ -409,6 +409,11 @@ public:
   /// value in \p Other.
   ConstantRange srem(const ConstantRange &Other) const;
 
+  /// Return a new range representing the possible values resulting from
+  /// a binary-xor of a value in this range by an all-one value,
+  /// aka bitwise complement operation.
+  ConstantRange binaryNot() const;
+
   /// Return a new range representing the possible values resulting
   /// from a binary-and of a value in this range by a value in \p Other.
   ConstantRange binaryAnd(const ConstantRange &Other) const;
diff --git a/llvm/lib/IR/ConstantRange.cpp b/llvm/lib/IR/ConstantRange.cpp
index 396c39b5b3a8..7b8dd66b993c 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();
 }
diff --git a/llvm/unittests/IR/ConstantRangeTest.cpp b/llvm/unittests/IR/ConstantRangeTest.cpp
index 8bcc6efdc265..474a94af3932 100644
--- a/llvm/unittests/IR/ConstantRangeTest.cpp
+++ b/llvm/unittests/IR/ConstantRangeTest.cpp
@@ -2349,4 +2349,22 @@ TEST_F(ConstantRangeTest, binaryXor) {
   EXPECT_TRUE(R0_99.binaryXor(R16_35).isFullSet());
 }
 
+TEST_F(ConstantRangeTest, binaryNot) {
+  TestUnsignedUnaryOpExhaustive(
+      [](const ConstantRange &CR) { return CR.binaryNot(); },
+      [](const APInt &N) { return ~N; });
+  TestUnsignedUnaryOpExhaustive(
+      [](const ConstantRange &CR) {
+        return CR.binaryXor(
+            ConstantRange(APInt::getAllOnesValue(CR.getBitWidth())));
+      },
+      [](const APInt &N) { return ~N; });
+  TestUnsignedUnaryOpExhaustive(
+      [](const ConstantRange &CR) {
+        return ConstantRange(APInt::getAllOnesValue(CR.getBitWidth()))
+            .binaryXor(CR);
+      },
+      [](const APInt &N) { return ~N; });
+}
+
 }  // anonymous namespace