[ConstantRange] Expand makeAllowedICmpRegion to use samesign to give tighter range

llvm/include/llvm/IR/ConstantRange.h

@@ -41,6 +41,7 @@ namespace llvm {
 
 class MDNode;
 class raw_ostream;
+class CmpPredicate;
 struct KnownBits;
 
 /// This class represents a range of values.
@@ -106,7 +107,7 @@ class [[nodiscard]] ConstantRange {
   ///
   /// Example: Pred = ult and Other = i8 [2, 5) returns Result = [0, 4)
   LLVM_ABI static ConstantRange
-  makeAllowedICmpRegion(CmpInst::Predicate Pred, const ConstantRange &Other);
+  makeAllowedICmpRegion(CmpPredicate Pred, const ConstantRange &Other);
 
   /// Produce the largest range such that all values in the returned range
   /// satisfy the given predicate with all values contained within Other.

llvm/lib/Analysis/ValueTracking.cpp

@@ -10325,7 +10325,7 @@ ConstantRange llvm::computeConstantRange(const Value *V, bool ForSigned,
           computeConstantRange(Cmp->getOperand(1), /* ForSigned */ false,
                                UseInstrInfo, AC, I, DT, Depth + 1);
       CR = CR.intersectWith(
-          ConstantRange::makeAllowedICmpRegion(Cmp->getPredicate(), RHS));
+          ConstantRange::makeAllowedICmpRegion(Cmp->getCmpPredicate(), RHS));
     }
   }
 

llvm/lib/IR/ConstantRange.cpp

@@ -23,6 +23,7 @@
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/Config/llvm-config.h"
+#include "llvm/IR/CmpPredicate.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
@@ -106,7 +107,7 @@ std::pair<ConstantRange, ConstantRange> ConstantRange::splitPosNeg() const {
   return {intersectWith(PosFilter), intersectWith(NegFilter)};
 }
 
-ConstantRange ConstantRange::makeAllowedICmpRegion(CmpInst::Predicate Pred,
+ConstantRange ConstantRange::makeAllowedICmpRegion(CmpPredicate Pred,
                                                    const ConstantRange &CR) {
   if (CR.isEmptySet())
     return CR;
@@ -125,7 +126,26 @@ ConstantRange ConstantRange::makeAllowedICmpRegion(CmpInst::Predicate Pred,
     APInt UMax(CR.getUnsignedMax());
     if (UMax.isMinValue())
       return getEmpty(W);
-    return ConstantRange(APInt::getMinValue(W), std::move(UMax));
+    if (!Pred.hasSameSign())
+      return ConstantRange(APInt::getMinValue(W), std::move(UMax));
+    if (W == 1)
+      return getEmpty(W);
+
+    // deal with edge cases
+    APInt AugmentedUpper = CR.getUpper();
+    if (CR.getUnsignedMax().isMinSignedValue())
+      AugmentedUpper = APInt::getSignedMinValue(W);
+    else if (CR.getSignedMax().isMinValue())
+      AugmentedUpper = APInt::getMinValue(W);
+
+    if (AugmentedUpper == CR.getLower() && !CR.isFullSet())
+      return getEmpty(W);
+
+    ConstantRange Augmented(CR.getLower(), AugmentedUpper);
+    if (Augmented.isAllNonNegative() ||
+        (!Augmented.isAllNegative() && Augmented.isSignWrappedSet()))
+      return getNonEmpty(APInt::getMinValue(W), Augmented.getUnsignedMax());
+    return getNonEmpty(APInt::getSignedMinValue(W), Augmented.getSignedMax());
   }
   case CmpInst::ICMP_SLT: {
     APInt SMax(CR.getSignedMax());
@@ -134,14 +154,42 @@ ConstantRange ConstantRange::makeAllowedICmpRegion(CmpInst::Predicate Pred,
     return ConstantRange(APInt::getSignedMinValue(W), std::move(SMax));
   }
   case CmpInst::ICMP_ULE:
+    if (!Pred.hasSameSign())
+      return getNonEmpty(APInt::getMinValue(W), CR.getUnsignedMax() + 1);
+    if (W == 1)
+      return CR;
+    if (CR.isAllNegative() ||
+        (!CR.isAllNonNegative() && !CR.isSignWrappedSet()))
+      return getNonEmpty(APInt::getSignedMinValue(W), CR.getSignedMax() + 1);
     return getNonEmpty(APInt::getMinValue(W), CR.getUnsignedMax() + 1);
   case CmpInst::ICMP_SLE:
     return getNonEmpty(APInt::getSignedMinValue(W), CR.getSignedMax() + 1);
   case CmpInst::ICMP_UGT: {
     APInt UMin(CR.getUnsignedMin());
     if (UMin.isMaxValue())
       return getEmpty(W);
-    return ConstantRange(std::move(UMin) + 1, APInt::getZero(W));
+    if (!Pred.hasSameSign())
+      return ConstantRange(std::move(UMin) + 1, APInt::getZero(W));
+    if (W == 1)
+      return getEmpty(W);
+
+    // deal with edge cases
+    APInt AugmentedLower = CR.getLower();
+    if (CR.getLower().isMaxSignedValue())
+      AugmentedLower = APInt::getSignedMinValue(W);
+    else if (CR.getLower().isMaxValue())
+      AugmentedLower = APInt::getMinValue(W);
+
+    if (AugmentedLower == CR.getUpper())
+      return getEmpty(W);
+
+    ConstantRange Augmented(AugmentedLower, CR.getUpper());
+    if (Augmented.isAllNegative())
+      return getNonEmpty(Augmented.getSignedMin() + 1, APInt::getZero(W));
+    if (!Augmented.isAllNonNegative() && Augmented.isSignWrappedSet())
+      return getNonEmpty(Augmented.getUnsignedMin() + 1, APInt::getZero(W));
+    return getNonEmpty(Augmented.getSignedMin() + 1,
+                       APInt::getSignedMinValue(W));
   }
   case CmpInst::ICMP_SGT: {
     APInt SMin(CR.getSignedMin());
@@ -150,6 +198,12 @@ ConstantRange ConstantRange::makeAllowedICmpRegion(CmpInst::Predicate Pred,
     return ConstantRange(std::move(SMin) + 1, APInt::getSignedMinValue(W));
   }
   case CmpInst::ICMP_UGE:
+    if (!Pred.hasSameSign())
+      return getNonEmpty(CR.getUnsignedMin(), APInt::getZero(W));
+
+    if (CR.isAllNonNegative() ||
+        (!CR.isAllNegative() && !CR.isSignWrappedSet()))
+      return getNonEmpty(CR.getSignedMin(), APInt::getSignedMinValue(W));
     return getNonEmpty(CR.getUnsignedMin(), APInt::getZero(W));
   case CmpInst::ICMP_SGE:
     return getNonEmpty(CR.getSignedMin(), APInt::getSignedMinValue(W));

llvm/unittests/Analysis/ValueTrackingTest.cpp

@@ -3234,6 +3234,106 @@ TEST_F(ValueTrackingTest, ComputeConstantRange) {
     EXPECT_EQ(10, CR2.getUpper());
   }
 
+  {
+    // Assumptions:
+    //  * stride >= 5 (unsigned)
+    //
+    // stride = [5, 0)
+    auto M = parseModule(R"(
+  declare void @llvm.assume(i1)
+
+  define i32 @test(i32 %stride) {
+    %gt = icmp uge i32 %stride, 5
+    call void @llvm.assume(i1 %gt)
+    %stride.plus.one = add nsw nuw i32 %stride, 1
+    ret i32 %stride.plus.one
+  })");
+    Function *F = M->getFunction("test");
+
+    AssumptionCache AC(*F);
+    Value *Stride = &*F->arg_begin();
+
+    Instruction *I = &findInstructionByName(F, "stride.plus.one");
+    ConstantRange CR2 = computeConstantRange(Stride, false, true, &AC, I);
+    EXPECT_EQ(5, CR2.getLower());
+    EXPECT_EQ(0, CR2.getUpper());
+  }
+
+  {
+    // Assumptions:
+    //  * stride > 5 (unsigned)
+    //
+    // stride = [5, 0)
+    auto M = parseModule(R"(
+  declare void @llvm.assume(i1)
+
+  define i32 @test(i32 %stride) {
+    %gt = icmp ugt i32 %stride, 5
+    call void @llvm.assume(i1 %gt)
+    %stride.plus.one = add nsw nuw i32 %stride, 1
+    ret i32 %stride.plus.one
+  })");
+    Function *F = M->getFunction("test");
+
+    AssumptionCache AC(*F);
+    Value *Stride = &*F->arg_begin();
+
+    Instruction *I = &findInstructionByName(F, "stride.plus.one");
+    ConstantRange CR2 = computeConstantRange(Stride, false, true, &AC, I);
+    EXPECT_EQ(6, CR2.getLower());
+    EXPECT_EQ(0, CR2.getUpper());
+  }
+
+  {
+    // Assumptions:
+    //  * stride >= 5 (samesign unsigned)
+    //
+    // stride = [5, MIN_SIGNED)
+    auto M = parseModule(R"(
+  declare void @llvm.assume(i1)
+
+  define i32 @test(i32 %stride) {
+    %gt = icmp samesign uge i32 %stride, 5
+    call void @llvm.assume(i1 %gt)
+    %stride.plus.one = add nsw nuw i32 %stride, 1
+    ret i32 %stride.plus.one
+  })");
+    Function *F = M->getFunction("test");
+
+    AssumptionCache AC(*F);
+    Value *Stride = &*F->arg_begin();
+
+    Instruction *I = &findInstructionByName(F, "stride.plus.one");
+    ConstantRange CR2 = computeConstantRange(Stride, false, true, &AC, I);
+    EXPECT_EQ(5, CR2.getLower());
+    EXPECT_EQ(APInt::getSignedMinValue(32), CR2.getUpper());
+  }
+
+  {
+    // Assumptions:
+    //  * stride > 5 (samesign unsigned)
+    //
+    // stride = [5, MIN_SIGNED)
+    auto M = parseModule(R"(
+  declare void @llvm.assume(i1)
+
+  define i32 @test(i32 %stride) {
+    %gt = icmp samesign ugt i32 %stride, 5
+    call void @llvm.assume(i1 %gt)
+    %stride.plus.one = add nsw nuw i32 %stride, 1
+    ret i32 %stride.plus.one
+  })");
+    Function *F = M->getFunction("test");
+
+    AssumptionCache AC(*F);
+    Value *Stride = &*F->arg_begin();
+
+    Instruction *I = &findInstructionByName(F, "stride.plus.one");
+    ConstantRange CR2 = computeConstantRange(Stride, false, true, &AC, I);
+    EXPECT_EQ(6, CR2.getLower());
+    EXPECT_EQ(APInt::getSignedMinValue(32), CR2.getUpper());
+  }
+
   {
     // Assumptions:
     //  * stride >= 5

llvm/unittests/IR/ConstantRangeTest.cpp

@@ -10,6 +10,7 @@
 #include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/Sequence.h"
 #include "llvm/ADT/SmallBitVector.h"
+#include "llvm/IR/CmpPredicate.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/Support/KnownBits.h"
@@ -1730,6 +1731,64 @@ TEST(ConstantRange, MakeAllowedICmpRegionEdgeCases) {
                   .isFullSet());
 }
 
+template <typename SIV>
+auto getSameSignTester(SIV ShouldIncludeValue, CmpInst::Predicate Cmp) {
+  return [Cmp, ShouldIncludeValue](const ConstantRange &CR) {
+    uint32_t BitWidth = CR.getBitWidth();
+    unsigned Max = 1 << BitWidth;
+    SmallBitVector Elems(Max);
+    if (!CR.isEmptySet()) {
+      for (unsigned I : llvm::seq(Max)) {
+        APInt Current(BitWidth, I);
+        if (ShouldIncludeValue(Current, CR))
+          Elems.set(I);
+      }
+    }
+
+    CmpPredicate CmpPred(Cmp, true);
+    TestRange(ConstantRange::makeAllowedICmpRegion(CmpPred, CR), Elems,
+              PreferSmallest, {});
+  };
+}
+
+TEST(ConstantRange, MakeAllowedICmpRegionExaustive) {
+  EnumerateInterestingConstantRanges(getSameSignTester(
+      [](const APInt &A, const ConstantRange &B) {
+        if (A.isNegative())
+          return A.sge(B.getSignedMin());
+        return A.uge(B.getUnsignedMin());
+      },
+      ICmpInst::ICMP_UGE));
+
+  EnumerateInterestingConstantRanges(getSameSignTester(
+      [](const APInt &A, const ConstantRange &B) {
+        if (A.isNegative())
+          return A.sgt(B.getSignedMin());
+        return A.ugt(B.getUnsignedMin());
+      },
+      ICmpInst::ICMP_UGT));
+
+  EnumerateInterestingConstantRanges(getSameSignTester(
+      [](const APInt &A, const ConstantRange &B) {
+        if (A.isNegative() && B.getUnsignedMax().isNegative())
+          return A.sle(B.getUnsignedMax());
+        if (A.isNonNegative() && B.getSignedMax().isNonNegative())
+          return A.ule(B.getSignedMax());
+        return false;
+      },
+      ICmpInst::ICMP_ULE));
+
+  EnumerateInterestingConstantRanges(getSameSignTester(
+      [](const APInt &A, const ConstantRange &B) {
+        if (A.isNegative() && B.getUnsignedMax().isNegative())
+          return A.slt(B.getUnsignedMax());
+        if (A.isNonNegative() && B.getSignedMax().isNonNegative())
+          return A.ult(B.getSignedMax());
+        return false;
+      },
+      ICmpInst::ICMP_ULT));
+}
+
 TEST(ConstantRange, MakeExactICmpRegion) {
   for (unsigned Bits : {1, 4}) {
     EnumerateAPInts(Bits, [](const APInt &N) {