[IR] Add a makeNoWrapRegion method to ConstantRange

Summary: This will be used in a future change to ScalarEvolution.

Reviewers: hfinkel, reames, nlewycky

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13612

llvm-svn: 250975

include/llvm/IR/ConstantRange.h

@@ -82,6 +82,17 @@ public:
   static ConstantRange makeSatisfyingICmpRegion(CmpInst::Predicate Pred,
                                                 const ConstantRange &Other);
 
+  /// Return the largest range containing all X such that "X BinOpC C" does not
+  /// wrap (overflow).
+  ///
+  /// Example:
+  ///  typedef OverflowingBinaryOperator OBO;
+  ///  makeNoWrapRegion(Add, i8 1, OBO::NoSignedWrap) == [-128, 127)
+  ///  makeNoWrapRegion(Add, i8 1, OBO::NoUnsignedWrap) == [0, -1)
+  ///  makeNoWrapRegion(Add, i8 0, OBO::NoUnsignedWrap) == Full Set
+  static ConstantRange makeNoWrapRegion(Instruction::BinaryOps BinOp,
+                                        const APInt &C, unsigned NoWrapKind);
+
   /// Return the lower value for this range.
   ///
   const APInt &getLower() const { return Lower; }

lib/IR/ConstantRange.cpp

@@ -21,7 +21,9 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/IR/Instruction.h"
 #include "llvm/IR/InstrTypes.h"
+#include "llvm/IR/Operator.h"
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
@@ -125,6 +127,57 @@ ConstantRange ConstantRange::makeSatisfyingICmpRegion(CmpInst::Predicate Pred,
       .inverse();
 }
 
+ConstantRange ConstantRange::makeNoWrapRegion(Instruction::BinaryOps BinOp,
+                                              const APInt &C,
+                                              unsigned NoWrapKind) {
+  typedef OverflowingBinaryOperator OBO;
+
+  // Computes the intersection of CR0 and CR1.  It is different from
+  // intersectWith in that the ConstantRange returned will only contain elements
+  // in both CR0 and CR1 (i.e. SubsetIntersect(X, Y) is a *subset*, proper or
+  // not, of both X and Y).
+  auto SubsetIntersect =
+      [](const ConstantRange &CR0, const ConstantRange &CR1) {
+    return CR0.inverse().unionWith(CR1.inverse()).inverse();
+  };
+
+  assert(BinOp >= Instruction::BinaryOpsBegin &&
+         BinOp < Instruction::BinaryOpsEnd && "Binary operators only!");
+
+  assert((NoWrapKind == OBO::NoSignedWrap ||
+          NoWrapKind == OBO::NoUnsignedWrap ||
+          NoWrapKind == (OBO::NoUnsignedWrap | OBO::NoSignedWrap)) &&
+         "NoWrapKind invalid!");
+
+  unsigned BitWidth = C.getBitWidth();
+  if (BinOp != Instruction::Add)
+    // Conservative answer: empty set
+    return ConstantRange(BitWidth, false);
+
+  if (C.isMinValue())
+    // Full set: nothing signed / unsigned wraps when added to 0.
+    return ConstantRange(BitWidth);
+
+  ConstantRange Result(BitWidth);
+
+  if (NoWrapKind & OBO::NoUnsignedWrap)
+    Result = SubsetIntersect(Result,
+                             ConstantRange(APInt::getNullValue(BitWidth), -C));
+
+  if (NoWrapKind & OBO::NoSignedWrap) {
+    if (C.isStrictlyPositive())
+      Result = SubsetIntersect(
+          Result, ConstantRange(APInt::getSignedMinValue(BitWidth),
+                                APInt::getSignedMinValue(BitWidth) - C));
+    else
+      Result = SubsetIntersect(
+          Result, ConstantRange(APInt::getSignedMinValue(BitWidth) - C,
+                                APInt::getSignedMinValue(BitWidth)));
+  }
+
+  return Result;
+}
+
 /// isFullSet - Return true if this set contains all of the elements possible
 /// for this data-type
 bool ConstantRange::isFullSet() const {

unittests/IR/ConstantRangeTest.cpp

@@ -9,6 +9,7 @@
 
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/Operator.h"
 #include "gtest/gtest.h"
 
 using namespace llvm;
@@ -568,4 +569,55 @@ TEST(ConstantRange, MakeSatisfyingICmpRegion) {
       ConstantRange(APInt(8, 4), APInt(8, -128)));
 }
 
+TEST(ConstantRange, MakeOverflowingRegion) {
+  const int IntMin4Bits = 8;
+  const int IntMax4Bits = 7;
+  typedef OverflowingBinaryOperator OBO;
+
+  for (int Const : {0, -1, -2, 1, 2, IntMin4Bits, IntMax4Bits}) {
+    APInt C(4, Const, true /* = isSigned */);
+
+    auto NUWRegion =
+      ConstantRange::makeNoWrapRegion(Instruction::Add, C, OBO::NoUnsignedWrap);
+
+    EXPECT_FALSE(NUWRegion.isEmptySet());
+
+    auto NSWRegion =
+      ConstantRange::makeNoWrapRegion(Instruction::Add, C, OBO::NoSignedWrap);
+
+    EXPECT_FALSE(NSWRegion.isEmptySet());
+
+    auto NoWrapRegion = ConstantRange::makeNoWrapRegion(
+        Instruction::Add, C, OBO::NoSignedWrap | OBO::NoUnsignedWrap);
+
+    EXPECT_FALSE(NoWrapRegion.isEmptySet());
+    EXPECT_TRUE(NUWRegion.intersectWith(NSWRegion).contains(NoWrapRegion));
+
+    for (APInt I = NUWRegion.getLower(), E = NUWRegion.getUpper(); I != E;
+         ++I) {
+      bool Overflow = false;
+      I.uadd_ov(C, Overflow);
+      EXPECT_FALSE(Overflow);
+    }
+
+    for (APInt I = NSWRegion.getLower(), E = NSWRegion.getUpper(); I != E;
+         ++I) {
+      bool Overflow = false;
+      I.sadd_ov(C, Overflow);
+      EXPECT_FALSE(Overflow);
+    }
+
+    for (APInt I = NoWrapRegion.getLower(), E = NoWrapRegion.getUpper(); I != E;
+         ++I) {
+      bool Overflow = false;
+
+      I.sadd_ov(C, Overflow);
+      EXPECT_FALSE(Overflow);
+
+      I.uadd_ov(C, Overflow);
+      EXPECT_FALSE(Overflow);
+    }
+  }
+}
+
 }  // anonymous namespace