[ConstantRange] Add srem() support

Add support for srem() to ConstantRange so we can use it in LVI. For
srem the sign of the result matches the sign of the LHS. For the RHS
only the absolute value is important. Apart from that the logic is
like urem.

Just like for urem this is only an approximate implementation. The tests
check a few specific cases and run an exhaustive test for conservative
correctness (but not exactness).

Differential Revision: https://reviews.llvm.org/D61207

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@360055 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/IR/ConstantRange.h b/include/llvm/IR/ConstantRange.h
index 0aac24ff8f71e2f93e5a6400013377a72b56d9b5..f8d4e0a4a9a8c737d5d1650769d36be0165c350e 100644 (file)
--- a/include/llvm/IR/ConstantRange.h
+++ b/include/llvm/IR/ConstantRange.h
@@ -369,6 +369,11 @@ public:
   /// value in \p Other.
   ConstantRange urem(const ConstantRange &Other) const;
 
+  /// Return a new range representing the possible values resulting
+  /// from a signed remainder operation of a value in this range and a
+  /// value in \p Other.
+  ConstantRange srem(const ConstantRange &Other) 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/lib/IR/ConstantRange.cpp b/lib/IR/ConstantRange.cpp
index e40bbbb7e9a2daab0a87dba899c5fbe812fcebe6..7079d0e8251d4a60d62b92084ed0644aa689ae4f 100644 (file)
--- a/lib/IR/ConstantRange.cpp
+++ b/lib/IR/ConstantRange.cpp
@@ -804,6 +804,8 @@ ConstantRange ConstantRange::binaryOp(Instruction::BinaryOps BinOp,
     return udiv(Other);
   case Instruction::URem:
     return urem(Other);
+  case Instruction::SRem:
+    return srem(Other);
   case Instruction::Shl:
     return shl(Other);
   case Instruction::LShr:
@@ -1010,6 +1012,48 @@ ConstantRange ConstantRange::urem(const ConstantRange &RHS) const {
   return getNonEmpty(APInt::getNullValue(getBitWidth()), std::move(Upper));
 }
 
+ConstantRange ConstantRange::srem(const ConstantRange &RHS) const {
+  if (isEmptySet() || RHS.isEmptySet())
+    return getEmpty();
+
+  ConstantRange AbsRHS = RHS.abs();
+  APInt MinAbsRHS = AbsRHS.getUnsignedMin();
+  APInt MaxAbsRHS = AbsRHS.getUnsignedMax();
+
+  // Modulus by zero is UB.
+  if (MaxAbsRHS.isNullValue())
+    return getEmpty();
+
+  if (MinAbsRHS.isNullValue())
+    ++MinAbsRHS;
+
+  APInt MinLHS = getSignedMin(), MaxLHS = getSignedMax();
+
+  if (MinLHS.isNonNegative()) {
+    // L % R for L < R is L.
+    if (MaxLHS.ult(MinAbsRHS))
+      return *this;
+
+    // L % R is <= L and < R.
+    APInt Upper = APIntOps::umin(MaxLHS, MaxAbsRHS - 1) + 1;
+    return ConstantRange(APInt::getNullValue(getBitWidth()), std::move(Upper));
+  }
+
+  // Same basic logic as above, but the result is negative.
+  if (MaxLHS.isNegative()) {
+    if (MinLHS.ugt(-MinAbsRHS))
+      return *this;
+
+    APInt Lower = APIntOps::umax(MinLHS, -MaxAbsRHS + 1);
+    return ConstantRange(std::move(Lower), APInt(getBitWidth(), 1));
+  }
+
+  // LHS range crosses zero.
+  APInt Lower = APIntOps::umax(MinLHS, -MaxAbsRHS + 1);
+  APInt Upper = APIntOps::umin(MaxLHS, MaxAbsRHS - 1) + 1;
+  return ConstantRange(std::move(Lower), std::move(Upper));
+}
+
 ConstantRange
 ConstantRange::binaryAnd(const ConstantRange &Other) const {
   if (isEmptySet() || Other.isEmptySet())

diff --git a/unittests/IR/ConstantRangeTest.cpp b/unittests/IR/ConstantRangeTest.cpp
index b6a794f0918762eba044d3bb5a6f36ca70e495f0..4709baad346ea6d6963aff0c7c6523d42ad7315a 100644 (file)
--- a/unittests/IR/ConstantRangeTest.cpp
+++ b/unittests/IR/ConstantRangeTest.cpp
@@ -96,20 +96,19 @@ static void TestUnsignedBinOpExhaustive(
 }
 
 template<typename Fn1, typename Fn2>
-static void TestSignedBinOpExhaustive(Fn1 RangeFn, Fn2 IntFn) {
+static void TestSignedBinOpExhaustive(
+    Fn1 RangeFn, Fn2 IntFn,
+    bool SkipZeroRHS = false, bool CorrectnessOnly = false) {
   unsigned Bits = 4;
   EnumerateTwoConstantRanges(Bits, [&](const ConstantRange &CR1,
                                        const ConstantRange &CR2) {
-    ConstantRange CR = RangeFn(CR1, CR2);
-    if (CR1.isEmptySet() || CR2.isEmptySet()) {
-      EXPECT_TRUE(CR.isEmptySet());
-      return;
-    }
-
     APInt Min = APInt::getSignedMaxValue(Bits);
     APInt Max = APInt::getSignedMinValue(Bits);
     ForeachNumInConstantRange(CR1, [&](const APInt &N1) {
       ForeachNumInConstantRange(CR2, [&](const APInt &N2) {
+        if (SkipZeroRHS && N2 == 0)
+          return;
+
         APInt N = IntFn(N1, N2);
         if (N.slt(Min))
           Min = N;
@@ -118,7 +117,18 @@ static void TestSignedBinOpExhaustive(Fn1 RangeFn, Fn2 IntFn) {
       });
     });
 
-    EXPECT_EQ(ConstantRange::getNonEmpty(Min, Max + 1), CR);
+    ConstantRange CR = RangeFn(CR1, CR2);
+    if (Min.sgt(Max)) {
+      EXPECT_TRUE(CR.isEmptySet());
+      return;
+    }
+
+    ConstantRange Exact = ConstantRange::getNonEmpty(Min, Max + 1);
+    if (CorrectnessOnly) {
+      EXPECT_TRUE(CR.contains(Exact));
+    } else {
+      EXPECT_EQ(Exact, CR);
+    }
   });
 }
 
@@ -870,6 +880,79 @@ TEST_F(ConstantRangeTest, URem) {
       /* SkipZeroRHS */ true, /* CorrectnessOnly */ true);
 }
 
+TEST_F(ConstantRangeTest, SRem) {
+  EXPECT_EQ(Full.srem(Empty), Empty);
+  EXPECT_EQ(Empty.srem(Full), Empty);
+  // srem by zero is UB.
+  EXPECT_EQ(Full.srem(ConstantRange(APInt(16, 0))), Empty);
+  // srem by full range doesn't contain SignedMinValue.
+  EXPECT_EQ(Full.srem(Full), ConstantRange(APInt::getSignedMinValue(16) + 1,
+                                           APInt::getSignedMinValue(16)));
+
+  ConstantRange PosMod(APInt(16, 10), APInt(16, 21));  // [10, 20]
+  ConstantRange NegMod(APInt(16, -20), APInt(16, -9)); // [-20, -10]
+  ConstantRange IntMinMod(APInt::getSignedMinValue(16));
+
+  ConstantRange Expected(16, true);
+
+  // srem is bounded by abs(RHS) minus one.
+  ConstantRange PosLargeLHS(APInt(16, 0), APInt(16, 41));
+  Expected = ConstantRange(APInt(16, 0), APInt(16, 20));
+  EXPECT_EQ(PosLargeLHS.srem(PosMod), Expected);
+  EXPECT_EQ(PosLargeLHS.srem(NegMod), Expected);
+  ConstantRange NegLargeLHS(APInt(16, -40), APInt(16, 1));
+  Expected = ConstantRange(APInt(16, -19), APInt(16, 1));
+  EXPECT_EQ(NegLargeLHS.srem(PosMod), Expected);
+  EXPECT_EQ(NegLargeLHS.srem(NegMod), Expected);
+  ConstantRange PosNegLargeLHS(APInt(16, -32), APInt(16, 38));
+  Expected = ConstantRange(APInt(16, -19), APInt(16, 20));
+  EXPECT_EQ(PosNegLargeLHS.srem(PosMod), Expected);
+  EXPECT_EQ(PosNegLargeLHS.srem(NegMod), Expected);
+
+  // srem is bounded by LHS.
+  ConstantRange PosLHS(APInt(16, 0), APInt(16, 16));
+  EXPECT_EQ(PosLHS.srem(PosMod), PosLHS);
+  EXPECT_EQ(PosLHS.srem(NegMod), PosLHS);
+  EXPECT_EQ(PosLHS.srem(IntMinMod), PosLHS);
+  ConstantRange NegLHS(APInt(16, -15), APInt(16, 1));
+  EXPECT_EQ(NegLHS.srem(PosMod), NegLHS);
+  EXPECT_EQ(NegLHS.srem(NegMod), NegLHS);
+  EXPECT_EQ(NegLHS.srem(IntMinMod), NegLHS);
+  ConstantRange PosNegLHS(APInt(16, -12), APInt(16, 18));
+  EXPECT_EQ(PosNegLHS.srem(PosMod), PosNegLHS);
+  EXPECT_EQ(PosNegLHS.srem(NegMod), PosNegLHS);
+  EXPECT_EQ(PosNegLHS.srem(IntMinMod), PosNegLHS);
+
+  // srem is LHS if it is smaller than RHS.
+  ConstantRange PosSmallLHS(APInt(16, 3), APInt(16, 8));
+  EXPECT_EQ(PosSmallLHS.srem(PosMod), PosSmallLHS);
+  EXPECT_EQ(PosSmallLHS.srem(NegMod), PosSmallLHS);
+  EXPECT_EQ(PosSmallLHS.srem(IntMinMod), PosSmallLHS);
+  ConstantRange NegSmallLHS(APInt(16, -7), APInt(16, -2));
+  EXPECT_EQ(NegSmallLHS.srem(PosMod), NegSmallLHS);
+  EXPECT_EQ(NegSmallLHS.srem(NegMod), NegSmallLHS);
+  EXPECT_EQ(NegSmallLHS.srem(IntMinMod), NegSmallLHS);
+  ConstantRange PosNegSmallLHS(APInt(16, -3), APInt(16, 8));
+  EXPECT_EQ(PosNegSmallLHS.srem(PosMod), PosNegSmallLHS);
+  EXPECT_EQ(PosNegSmallLHS.srem(NegMod), PosNegSmallLHS);
+  EXPECT_EQ(PosNegSmallLHS.srem(IntMinMod), PosNegSmallLHS);
+
+  // Example of a suboptimal result:
+  // [12, 14] srem 10 is [2, 4], but we conservatively compute [0, 9].
+  EXPECT_EQ(ConstantRange(APInt(16, 12), APInt(16, 15))
+                .srem(ConstantRange(APInt(16, 10))),
+            ConstantRange(APInt(16, 0), APInt(16, 10)));
+
+  TestSignedBinOpExhaustive(
+      [](const ConstantRange &CR1, const ConstantRange &CR2) {
+        return CR1.srem(CR2);
+      },
+      [](const APInt &N1, const APInt &N2) {
+        return N1.srem(N2);
+      },
+      /* SkipZeroRHS */ true, /* CorrectnessOnly */ true);
+}
+
 TEST_F(ConstantRangeTest, Shl) {
   ConstantRange Some2(APInt(16, 0xfff), APInt(16, 0x8000));
   ConstantRange WrapNullMax(APInt(16, 0x1), APInt(16, 0x0));