[ValueTracking][ConstantRange] Distinguish low/high always overflow

In order to fold an always overflowing signed saturating add/sub,
we need to know in which direction the always overflow occurs.
This patch splits up AlwaysOverflows into AlwaysOverflowsLow and
AlwaysOverflowsHigh to pass through this information (but it is
not used yet).

Differential Revision: https://reviews.llvm.org/D62463

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@361858 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Analysis/ValueTracking.h b/include/llvm/Analysis/ValueTracking.h
index bc6be5833070a3b2f82db73e2ccf48caf77bfbc3..8e03b7773e8ec912d70d365400b3edc6dc409ee8 100644 (file)
--- a/include/llvm/Analysis/ValueTracking.h
+++ b/include/llvm/Analysis/ValueTracking.h
@@ -412,7 +412,16 @@ class Value;
   bool isValidAssumeForContext(const Instruction *I, const Instruction *CxtI,
                                const DominatorTree *DT = nullptr);
 
-  enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows };
+  enum class OverflowResult {
+    /// Always overflows in the direction of signed/unsigned min value.
+    AlwaysOverflowsLow,
+    /// Always overflows in the direction of signed/unsigned max value.
+    AlwaysOverflowsHigh,
+    /// May or may not overflow.
+    MayOverflow,
+    /// Never overflows.
+    NeverOverflows,
+  };
 
   OverflowResult computeOverflowForUnsignedMul(const Value *LHS,
                                                const Value *RHS,

diff --git a/include/llvm/IR/ConstantRange.h b/include/llvm/IR/ConstantRange.h
index f8d4e0a4a9a8c737d5d1650769d36be0165c350e..0b176747f7c0f28bb439bdafc581263665f4e906 100644 (file)
--- a/include/llvm/IR/ConstantRange.h
+++ b/include/llvm/IR/ConstantRange.h
@@ -416,7 +416,16 @@ public:
 
   /// Represents whether an operation on the given constant range is known to
   /// always or never overflow.
-  enum class OverflowResult { AlwaysOverflows, MayOverflow, NeverOverflows };
+  enum class OverflowResult {
+    /// Always overflows in the direction of signed/unsigned min value.
+    AlwaysOverflowsLow,
+    /// Always overflows in the direction of signed/unsigned max value.
+    AlwaysOverflowsHigh,
+    /// May or may not overflow.
+    MayOverflow,
+    /// Never overflows.
+    NeverOverflows,
+  };
 
   /// Return whether unsigned add of the two ranges always/never overflows.
   OverflowResult unsignedAddMayOverflow(const ConstantRange &Other) const;

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index d46ddc428b266246bcad457391ebf8405eb13f7d..640063700e8840182246673b1bc95f8c6988bdaf 100644 (file)
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -3992,8 +3992,10 @@ static OverflowResult mapOverflowResult(ConstantRange::OverflowResult OR) {
   switch (OR) {
     case ConstantRange::OverflowResult::MayOverflow:
       return OverflowResult::MayOverflow;
-    case ConstantRange::OverflowResult::AlwaysOverflows:
-      return OverflowResult::AlwaysOverflows;
+    case ConstantRange::OverflowResult::AlwaysOverflowsLow:
+      return OverflowResult::AlwaysOverflowsLow;
+    case ConstantRange::OverflowResult::AlwaysOverflowsHigh:
+      return OverflowResult::AlwaysOverflowsHigh;
     case ConstantRange::OverflowResult::NeverOverflows:
       return OverflowResult::NeverOverflows;
   }

diff --git a/lib/IR/ConstantRange.cpp b/lib/IR/ConstantRange.cpp
index 0d44c3815b3b44b0f13551a98bb37730617e16b4..30b6a27078c2c2322c057c4beb2c0b263d06d6ca 100644 (file)
--- a/lib/IR/ConstantRange.cpp
+++ b/lib/IR/ConstantRange.cpp
@@ -1208,9 +1208,9 @@ ConstantRange::OverflowResult ConstantRange::unsignedAddMayOverflow(
   APInt Min = getUnsignedMin(), Max = getUnsignedMax();
   APInt OtherMin = Other.getUnsignedMin(), OtherMax = Other.getUnsignedMax();
 
-  // a u+ b overflows iff a u> ~b.
+  // a u+ b overflows high iff a u> ~b.
   if (Min.ugt(~OtherMin))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsHigh;
   if (Max.ugt(~OtherMax))
     return OverflowResult::MayOverflow;
   return OverflowResult::NeverOverflows;
@@ -1231,10 +1231,10 @@ ConstantRange::OverflowResult ConstantRange::signedAddMayOverflow(
   // a s+ b overflows low iff a s< 0 && b s< 0 && a s< smin - b.
   if (Min.isNonNegative() && OtherMin.isNonNegative() &&
       Min.sgt(SignedMax - OtherMin))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsHigh;
   if (Max.isNegative() && OtherMax.isNegative() &&
       Max.slt(SignedMin - OtherMax))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsLow;
 
   if (Max.isNonNegative() && OtherMax.isNonNegative() &&
       Max.sgt(SignedMax - OtherMax))
@@ -1254,9 +1254,9 @@ ConstantRange::OverflowResult ConstantRange::unsignedSubMayOverflow(
   APInt Min = getUnsignedMin(), Max = getUnsignedMax();
   APInt OtherMin = Other.getUnsignedMin(), OtherMax = Other.getUnsignedMax();
 
-  // a u- b overflows iff a u< b.
+  // a u- b overflows low iff a u< b.
   if (Max.ult(OtherMin))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsLow;
   if (Min.ult(OtherMax))
     return OverflowResult::MayOverflow;
   return OverflowResult::NeverOverflows;
@@ -1277,10 +1277,10 @@ ConstantRange::OverflowResult ConstantRange::signedSubMayOverflow(
   // a s- b overflows low iff a s< 0 && b s>= 0 && a s< smin + b.
   if (Min.isNonNegative() && OtherMax.isNegative() &&
       Min.sgt(SignedMax + OtherMax))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsHigh;
   if (Max.isNegative() && OtherMin.isNonNegative() &&
       Max.slt(SignedMin + OtherMin))
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsLow;
 
   if (Max.isNonNegative() && OtherMin.isNegative() &&
       Max.sgt(SignedMax + OtherMin))
@@ -1303,7 +1303,7 @@ ConstantRange::OverflowResult ConstantRange::unsignedMulMayOverflow(
 
   (void) Min.umul_ov(OtherMin, Overflow);
   if (Overflow)
-    return OverflowResult::AlwaysOverflows;
+    return OverflowResult::AlwaysOverflowsHigh;
 
   (void) Max.umul_ov(OtherMax, Overflow);
   if (Overflow)

diff --git a/lib/Transforms/InstCombine/InstCombineCalls.cpp b/lib/Transforms/InstCombine/InstCombineCalls.cpp
index e2813f9d9d496bd65e6edbdde59da49e24388b48..a18043ef33f8c90460f0a665625fb54dd7edb411 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2064,7 +2064,7 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
       OR = computeOverflowForUnsignedAdd(Arg0, Arg1, II);
       if (OR == OverflowResult::NeverOverflows)
         return BinaryOperator::CreateNUWAdd(Arg0, Arg1);
-      if (OR == OverflowResult::AlwaysOverflows)
+      if (OR == OverflowResult::AlwaysOverflowsHigh)
         return replaceInstUsesWith(*II,
                                    ConstantInt::getAllOnesValue(II->getType()));
       break;
@@ -2072,7 +2072,7 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
       OR = computeOverflowForUnsignedSub(Arg0, Arg1, II);
       if (OR == OverflowResult::NeverOverflows)
         return BinaryOperator::CreateNUWSub(Arg0, Arg1);
-      if (OR == OverflowResult::AlwaysOverflows)
+      if (OR == OverflowResult::AlwaysOverflowsLow)
         return replaceInstUsesWith(*II,
                                    ConstantInt::getNullValue(II->getType()));
       break;

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index ab2da177d7b2eb1c7d4d56d635875af7d48d3c1b..b3eb75ea8a8b72034909f295ec5ac4c3a8e78d06 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3993,7 +3993,8 @@ bool InstCombiner::OptimizeOverflowCheck(
   switch (computeOverflow(BinaryOp, IsSigned, LHS, RHS, &OrigI)) {
     case OverflowResult::MayOverflow:
       return false;
-    case OverflowResult::AlwaysOverflows:
+    case OverflowResult::AlwaysOverflowsLow:
+    case OverflowResult::AlwaysOverflowsHigh:
       Result = Builder.CreateBinOp(BinaryOp, LHS, RHS);
       Result->takeName(&OrigI);
       Overflow = Builder.getTrue();

diff --git a/unittests/IR/ConstantRangeTest.cpp b/unittests/IR/ConstantRangeTest.cpp
index 4709baad346ea6d6963aff0c7c6523d42ad7315a..eeebe2e73ae24b0881c148137a90fcf16aaf7fff 100644 (file)
--- a/unittests/IR/ConstantRangeTest.cpp
+++ b/unittests/IR/ConstantRangeTest.cpp
@@ -1487,8 +1487,10 @@ TEST(ConstantRange, MakeGuaranteedNoWrapRegionMulSignedRange) {
 
 #define EXPECT_MAY_OVERFLOW(op) \
   EXPECT_EQ(ConstantRange::OverflowResult::MayOverflow, (op))
-#define EXPECT_ALWAYS_OVERFLOWS(op) \
-  EXPECT_EQ(ConstantRange::OverflowResult::AlwaysOverflows, (op))
+#define EXPECT_ALWAYS_OVERFLOWS_LOW(op) \
+  EXPECT_EQ(ConstantRange::OverflowResult::AlwaysOverflowsLow, (op))
+#define EXPECT_ALWAYS_OVERFLOWS_HIGH(op) \
+  EXPECT_EQ(ConstantRange::OverflowResult::AlwaysOverflowsHigh, (op))
 #define EXPECT_NEVER_OVERFLOWS(op) \
   EXPECT_EQ(ConstantRange::OverflowResult::NeverOverflows, (op))
 
@@ -1521,9 +1523,9 @@ TEST_F(ConstantRangeTest, UnsignedAddOverflow) {
   ConstantRange C1(APInt(16, 0x0299), APInt(16, 0x0400));
   ConstantRange C2(APInt(16, 0x0300), APInt(16, 0x0400));
   EXPECT_MAY_OVERFLOW(A.unsignedAddMayOverflow(C1));
-  EXPECT_ALWAYS_OVERFLOWS(A.unsignedAddMayOverflow(C2));
+  EXPECT_ALWAYS_OVERFLOWS_HIGH(A.unsignedAddMayOverflow(C2));
   EXPECT_MAY_OVERFLOW(C1.unsignedAddMayOverflow(A));
-  EXPECT_ALWAYS_OVERFLOWS(C2.unsignedAddMayOverflow(A));
+  EXPECT_ALWAYS_OVERFLOWS_HIGH(C2.unsignedAddMayOverflow(A));
 }
 
 TEST_F(ConstantRangeTest, UnsignedSubOverflow) {
@@ -1548,7 +1550,7 @@ TEST_F(ConstantRangeTest, UnsignedSubOverflow) {
   ConstantRange A(APInt(16, 0x0000), APInt(16, 0x0100));
   ConstantRange B(APInt(16, 0x0100), APInt(16, 0x0200));
   EXPECT_NEVER_OVERFLOWS(B.unsignedSubMayOverflow(A));
-  EXPECT_ALWAYS_OVERFLOWS(A.unsignedSubMayOverflow(B));
+  EXPECT_ALWAYS_OVERFLOWS_LOW(A.unsignedSubMayOverflow(B));
 
   ConstantRange A1(APInt(16, 0x0000), APInt(16, 0x0101));
   ConstantRange B1(APInt(16, 0x0100), APInt(16, 0x0201));
@@ -1591,7 +1593,7 @@ TEST_F(ConstantRangeTest, SignedAddOverflow) {
   ConstantRange B5(APInt(16, 0x0299), APInt(16, 0x0400));
   ConstantRange B6(APInt(16, 0x0300), APInt(16, 0x0400));
   EXPECT_MAY_OVERFLOW(A.signedAddMayOverflow(B5));
-  EXPECT_ALWAYS_OVERFLOWS(A.signedAddMayOverflow(B6));
+  EXPECT_ALWAYS_OVERFLOWS_HIGH(A.signedAddMayOverflow(B6));
 
   ConstantRange C(APInt(16, 0x8200), APInt(16, 0x8300));
   ConstantRange D1(APInt(16, 0xfe00), APInt(16, 0xff00));
@@ -1605,7 +1607,7 @@ TEST_F(ConstantRangeTest, SignedAddOverflow) {
   ConstantRange D5(APInt(16, 0xfc00), APInt(16, 0xfd02));
   ConstantRange D6(APInt(16, 0xfc00), APInt(16, 0xfd01));
   EXPECT_MAY_OVERFLOW(C.signedAddMayOverflow(D5));
-  EXPECT_ALWAYS_OVERFLOWS(C.signedAddMayOverflow(D6));
+  EXPECT_ALWAYS_OVERFLOWS_LOW(C.signedAddMayOverflow(D6));
 
   ConstantRange E(APInt(16, 0xff00), APInt(16, 0x0100));
   EXPECT_NEVER_OVERFLOWS(E.signedAddMayOverflow(E));
@@ -1637,7 +1639,7 @@ TEST_F(ConstantRangeTest, SignedSubOverflow) {
   ConstantRange B3(APInt(16, 0xfc00), APInt(16, 0xfd02));
   ConstantRange B4(APInt(16, 0xfc00), APInt(16, 0xfd01));
   EXPECT_MAY_OVERFLOW(A.signedSubMayOverflow(B3));
-  EXPECT_ALWAYS_OVERFLOWS(A.signedSubMayOverflow(B4));
+  EXPECT_ALWAYS_OVERFLOWS_HIGH(A.signedSubMayOverflow(B4));
 
   ConstantRange C(APInt(16, 0x8200), APInt(16, 0x8300));
   ConstantRange D1(APInt(16, 0x0100), APInt(16, 0x0201));
@@ -1647,7 +1649,7 @@ TEST_F(ConstantRangeTest, SignedSubOverflow) {
   ConstantRange D3(APInt(16, 0x0299), APInt(16, 0x0400));
   ConstantRange D4(APInt(16, 0x0300), APInt(16, 0x0400));
   EXPECT_MAY_OVERFLOW(C.signedSubMayOverflow(D3));
-  EXPECT_ALWAYS_OVERFLOWS(C.signedSubMayOverflow(D4));
+  EXPECT_ALWAYS_OVERFLOWS_LOW(C.signedSubMayOverflow(D4));
 
   ConstantRange E(APInt(16, 0xff00), APInt(16, 0x0100));
   EXPECT_NEVER_OVERFLOWS(E.signedSubMayOverflow(E));
@@ -1663,25 +1665,39 @@ static void TestOverflowExhaustive(Fn1 OverflowFn, Fn2 MayOverflowFn) {
                                        const ConstantRange &CR2) {
     // Loop over all N1 in CR1 and N2 in CR2 and check whether any of the
     // operations have overflow / have no overflow.
-    bool RangeHasOverflow = false;
+    bool RangeHasOverflowLow = false;
+    bool RangeHasOverflowHigh = false;
     bool RangeHasNoOverflow = false;
     ForeachNumInConstantRange(CR1, [&](const APInt &N1) {
       ForeachNumInConstantRange(CR2, [&](const APInt &N2) {
-        if (OverflowFn(N1, N2))
-          RangeHasOverflow = true;
-        else
+        bool IsOverflowHigh;
+        if (!OverflowFn(IsOverflowHigh, N1, N2)) {
           RangeHasNoOverflow = true;
+          return;
+        }
+
+        if (IsOverflowHigh)
+          RangeHasOverflowHigh = true;
+        else
+          RangeHasOverflowLow = true;
       });
     });
 
     ConstantRange::OverflowResult OR = MayOverflowFn(CR1, CR2);
     switch (OR) {
-    case ConstantRange::OverflowResult::AlwaysOverflows:
-      EXPECT_TRUE(RangeHasOverflow);
+    case ConstantRange::OverflowResult::AlwaysOverflowsLow:
+      EXPECT_TRUE(RangeHasOverflowLow);
+      EXPECT_FALSE(RangeHasOverflowHigh);
+      EXPECT_FALSE(RangeHasNoOverflow);
+      break;
+    case ConstantRange::OverflowResult::AlwaysOverflowsHigh:
+      EXPECT_TRUE(RangeHasOverflowHigh);
+      EXPECT_FALSE(RangeHasOverflowLow);
       EXPECT_FALSE(RangeHasNoOverflow);
       break;
     case ConstantRange::OverflowResult::NeverOverflows:
-      EXPECT_FALSE(RangeHasOverflow);
+      EXPECT_FALSE(RangeHasOverflowLow);
+      EXPECT_FALSE(RangeHasOverflowHigh);
       EXPECT_TRUE(RangeHasNoOverflow);
       break;
     case ConstantRange::OverflowResult::MayOverflow:
@@ -1691,7 +1707,7 @@ static void TestOverflowExhaustive(Fn1 OverflowFn, Fn2 MayOverflowFn) {
       if (CR1.isEmptySet() || CR2.isEmptySet())
         break;
 
-      EXPECT_TRUE(RangeHasOverflow);
+      EXPECT_TRUE(RangeHasOverflowLow || RangeHasOverflowHigh);
       EXPECT_TRUE(RangeHasNoOverflow);
       break;
     }
@@ -1700,9 +1716,10 @@ static void TestOverflowExhaustive(Fn1 OverflowFn, Fn2 MayOverflowFn) {
 
 TEST_F(ConstantRangeTest, UnsignedAddOverflowExhaustive) {
   TestOverflowExhaustive(
-      [](const APInt &N1, const APInt &N2) {
+      [](bool &IsOverflowHigh, const APInt &N1, const APInt &N2) {
         bool Overflow;
         (void) N1.uadd_ov(N2, Overflow);
+        IsOverflowHigh = true;
         return Overflow;
       },
       [](const ConstantRange &CR1, const ConstantRange &CR2) {
@@ -1712,9 +1729,10 @@ TEST_F(ConstantRangeTest, UnsignedAddOverflowExhaustive) {
 
 TEST_F(ConstantRangeTest, UnsignedSubOverflowExhaustive) {
   TestOverflowExhaustive(
-      [](const APInt &N1, const APInt &N2) {
+      [](bool &IsOverflowHigh, const APInt &N1, const APInt &N2) {
         bool Overflow;
         (void) N1.usub_ov(N2, Overflow);
+        IsOverflowHigh = false;
         return Overflow;
       },
       [](const ConstantRange &CR1, const ConstantRange &CR2) {
@@ -1724,9 +1742,10 @@ TEST_F(ConstantRangeTest, UnsignedSubOverflowExhaustive) {
 
 TEST_F(ConstantRangeTest, UnsignedMulOverflowExhaustive) {
   TestOverflowExhaustive(
-      [](const APInt &N1, const APInt &N2) {
+      [](bool &IsOverflowHigh, const APInt &N1, const APInt &N2) {
         bool Overflow;
         (void) N1.umul_ov(N2, Overflow);
+        IsOverflowHigh = true;
         return Overflow;
       },
       [](const ConstantRange &CR1, const ConstantRange &CR2) {
@@ -1736,9 +1755,10 @@ TEST_F(ConstantRangeTest, UnsignedMulOverflowExhaustive) {
 
 TEST_F(ConstantRangeTest, SignedAddOverflowExhaustive) {
   TestOverflowExhaustive(
-      [](const APInt &N1, const APInt &N2) {
+      [](bool &IsOverflowHigh, const APInt &N1, const APInt &N2) {
         bool Overflow;
         (void) N1.sadd_ov(N2, Overflow);
+        IsOverflowHigh = N1.isNonNegative();
         return Overflow;
       },
       [](const ConstantRange &CR1, const ConstantRange &CR2) {
@@ -1748,9 +1768,10 @@ TEST_F(ConstantRangeTest, SignedAddOverflowExhaustive) {
 
 TEST_F(ConstantRangeTest, SignedSubOverflowExhaustive) {
   TestOverflowExhaustive(
-      [](const APInt &N1, const APInt &N2) {
+      [](bool &IsOverflowHigh, const APInt &N1, const APInt &N2) {
         bool Overflow;
         (void) N1.ssub_ov(N2, Overflow);
+        IsOverflowHigh = N1.isNonNegative();
         return Overflow;
       },
       [](const ConstantRange &CR1, const ConstantRange &CR2) {