[SCEV] Unify getUnsignedRange and getSignedRange

Summary:
This removes some duplicated code, and also helps optimization: e.g. in
the test case added, `%idx ULT 128` in `@x` is not currently optimized
to `true` by `-indvars` but will be, after this change.

The only functional change in ths commit is that for add recurrences,
ScalarEvolution::getRange will be more aggressive -- computing the
unsigned (resp. signed) range for a SCEVAddRecExpr will now look at the
NSW (resp. NUW) bits and check for signed (resp. unsigned) overflow.
This can be a strict improvement in some cases (such as the attached
test case), and should be no worse in other cases.

Reviewers: atrick, nlewycky

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8142

llvm-svn: 231709

3 files changed, 185 insertions, 226 deletions

diff --git a/llvm/include/llvm/Analysis/ScalarEvolution.h b/llvm/include/llvm/Analysis/ScalarEvolution.h
index 29b535aa65f..979d3abb69d 100644
--- a/llvm/include/llvm/Analysis/ScalarEvolution.h
+++ b/llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -388,32 +388,31 @@ namespace llvm {
     /// computeBlockDisposition - Compute a BlockDisposition value.
     BlockDisposition computeBlockDisposition(const SCEV *S, const BasicBlock *BB);
 
-    /// UnsignedRanges - Memoized results from getUnsignedRange
+    /// UnsignedRanges - Memoized results from getRange
     DenseMap<const SCEV *, ConstantRange> UnsignedRanges;
 
-    /// SignedRanges - Memoized results from getSignedRange
+    /// SignedRanges - Memoized results from getRange
     DenseMap<const SCEV *, ConstantRange> SignedRanges;
 
-    /// setUnsignedRange - Set the memoized unsigned range for the given SCEV.
-    const ConstantRange &setUnsignedRange(const SCEV *S,
-                                          const ConstantRange &CR) {
-      std::pair<DenseMap<const SCEV *, ConstantRange>::iterator, bool> Pair =
-        UnsignedRanges.insert(std::make_pair(S, CR));
-      if (!Pair.second)
-        Pair.first->second = CR;
-      return Pair.first->second;
-    }
+    /// RangeSignHint - Used to parameterize getRange
+    enum RangeSignHint { HINT_RANGE_UNSIGNED, HINT_RANGE_SIGNED };
+
+    /// setRange - Set the memoized range for the given SCEV.
+    const ConstantRange &setRange(const SCEV *S, RangeSignHint Hint,
+                                  const ConstantRange &CR) {
+      DenseMap<const SCEV *, ConstantRange> &Cache =
+          Hint == HINT_RANGE_UNSIGNED ? UnsignedRanges : SignedRanges;
 
-    /// setUnsignedRange - Set the memoized signed range for the given SCEV.
-    const ConstantRange &setSignedRange(const SCEV *S,
-                                        const ConstantRange &CR) {
       std::pair<DenseMap<const SCEV *, ConstantRange>::iterator, bool> Pair =
-        SignedRanges.insert(std::make_pair(S, CR));
+          Cache.insert(std::make_pair(S, CR));
       if (!Pair.second)
         Pair.first->second = CR;
       return Pair.first->second;
     }
 
+    /// getRange - Determine the range for a particular SCEV.
+    ConstantRange getRange(const SCEV *S, RangeSignHint Hint);
+
     /// createSCEV - We know that there is no SCEV for the specified value.
     /// Analyze the expression.
     const SCEV *createSCEV(Value *V);
@@ -843,11 +842,15 @@ namespace llvm {
 
     /// getUnsignedRange - Determine the unsigned range for a particular SCEV.
     ///
-    ConstantRange getUnsignedRange(const SCEV *S);
+    ConstantRange getUnsignedRange(const SCEV *S) {
+      return getRange(S, HINT_RANGE_UNSIGNED);
+    }
 
     /// getSignedRange - Determine the signed range for a particular SCEV.
     ///
-    ConstantRange getSignedRange(const SCEV *S);
+    ConstantRange getSignedRange(const SCEV *S) {
+      return getRange(S, HINT_RANGE_SIGNED);
+    }
 
     /// isKnownNegative - Test if the given expression is known to be negative.
     ///
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index ce92e8c3469..3ccbd14438d 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3868,79 +3868,93 @@ static Optional<ConstantRange> GetRangeFromMetadata(Value *V) {
   return None;
 }
 
-/// getUnsignedRange - Determine the unsigned range for a particular SCEV.
+/// getRange - Determine the range for a particular SCEV.  If SignHint is
+/// HINT_RANGE_UNSIGNED (resp. HINT_RANGE_SIGNED) then getRange prefers ranges
+/// with a "cleaner" unsigned (resp. signed) representation.
 ///
 ConstantRange
-ScalarEvolution::getUnsignedRange(const SCEV *S) {
+ScalarEvolution::getRange(const SCEV *S,
+                          ScalarEvolution::RangeSignHint SignHint) {
+  DenseMap<const SCEV *, ConstantRange> &Cache =
+      SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED ? UnsignedRanges
+                                                       : SignedRanges;
+
   // See if we've computed this range already.
-  DenseMap<const SCEV *, ConstantRange>::iterator I = UnsignedRanges.find(S);
-  if (I != UnsignedRanges.end())
+  DenseMap<const SCEV *, ConstantRange>::iterator I = Cache.find(S);
+  if (I != Cache.end())
     return I->second;
 
   if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S))
-    return setUnsignedRange(C, ConstantRange(C->getValue()->getValue()));
+    return setRange(C, SignHint, ConstantRange(C->getValue()->getValue()));
 
   unsigned BitWidth = getTypeSizeInBits(S->getType());
   ConstantRange ConservativeResult(BitWidth, /*isFullSet=*/true);
 
-  // If the value has known zeros, the maximum unsigned value will have those
-  // known zeros as well.
+  // If the value has known zeros, the maximum value will have those known zeros
+  // as well.
   uint32_t TZ = GetMinTrailingZeros(S);
-  if (TZ != 0)
-    ConservativeResult =
-      ConstantRange(APInt::getMinValue(BitWidth),
-                    APInt::getMaxValue(BitWidth).lshr(TZ).shl(TZ) + 1);
+  if (TZ != 0) {
+    if (SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED)
+      ConservativeResult =
+          ConstantRange(APInt::getMinValue(BitWidth),
+                        APInt::getMaxValue(BitWidth).lshr(TZ).shl(TZ) + 1);
+    else
+      ConservativeResult = ConstantRange(
+          APInt::getSignedMinValue(BitWidth),
+          APInt::getSignedMaxValue(BitWidth).ashr(TZ).shl(TZ) + 1);
+  }
 
   if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
-    ConstantRange X = getUnsignedRange(Add->getOperand(0));
+    ConstantRange X = getRange(Add->getOperand(0), SignHint);
     for (unsigned i = 1, e = Add->getNumOperands(); i != e; ++i)
-      X = X.add(getUnsignedRange(Add->getOperand(i)));
-    return setUnsignedRange(Add, ConservativeResult.intersectWith(X));
+      X = X.add(getRange(Add->getOperand(i), SignHint));
+    return setRange(Add, SignHint, ConservativeResult.intersectWith(X));
   }
 
   if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) {
-    ConstantRange X = getUnsignedRange(Mul->getOperand(0));
+    ConstantRange X = getRange(Mul->getOperand(0), SignHint);
     for (unsigned i = 1, e = Mul->getNumOperands(); i != e; ++i)
-      X = X.multiply(getUnsignedRange(Mul->getOperand(i)));
-    return setUnsignedRange(Mul, ConservativeResult.intersectWith(X));
+      X = X.multiply(getRange(Mul->getOperand(i), SignHint));
+    return setRange(Mul, SignHint, ConservativeResult.intersectWith(X));
   }
 
   if (const SCEVSMaxExpr *SMax = dyn_cast<SCEVSMaxExpr>(S)) {
-    ConstantRange X = getUnsignedRange(SMax->getOperand(0));
+    ConstantRange X = getRange(SMax->getOperand(0), SignHint);
     for (unsigned i = 1, e = SMax->getNumOperands(); i != e; ++i)
-      X = X.smax(getUnsignedRange(SMax->getOperand(i)));
-    return setUnsignedRange(SMax, ConservativeResult.intersectWith(X));
+      X = X.smax(getRange(SMax->getOperand(i), SignHint));
+    return setRange(SMax, SignHint, ConservativeResult.intersectWith(X));
   }
 
   if (const SCEVUMaxExpr *UMax = dyn_cast<SCEVUMaxExpr>(S)) {
-    ConstantRange X = getUnsignedRange(UMax->getOperand(0));
+    ConstantRange X = getRange(UMax->getOperand(0), SignHint);
     for (unsigned i = 1, e = UMax->getNumOperands(); i != e; ++i)
-      X = X.umax(getUnsignedRange(UMax->getOperand(i)));
-    return setUnsignedRange(UMax, ConservativeResult.intersectWith(X));
+      X = X.umax(getRange(UMax->getOperand(i), SignHint));
+    return setRange(UMax, SignHint, ConservativeResult.intersectWith(X));
   }
 
   if (const SCEVUDivExpr *UDiv = dyn_cast<SCEVUDivExpr>(S)) {
-    ConstantRange X = getUnsignedRange(UDiv->getLHS());
-    ConstantRange Y = getUnsignedRange(UDiv->getRHS());
-    return setUnsignedRange(UDiv, ConservativeResult.intersectWith(X.udiv(Y)));
+    ConstantRange X = getRange(UDiv->getLHS(), SignHint);
+    ConstantRange Y = getRange(UDiv->getRHS(), SignHint);
+    return setRange(UDiv, SignHint,
+                    ConservativeResult.intersectWith(X.udiv(Y)));
   }
 
   if (const SCEVZeroExtendExpr *ZExt = dyn_cast<SCEVZeroExtendExpr>(S)) {
-    ConstantRange X = getUnsignedRange(ZExt->getOperand());
-    return setUnsignedRange(ZExt,
-      ConservativeResult.intersectWith(X.zeroExtend(BitWidth)));
+    ConstantRange X = getRange(ZExt->getOperand(), SignHint);
+    return setRange(ZExt, SignHint,
+                    ConservativeResult.intersectWith(X.zeroExtend(BitWidth)));
   }
 
   if (const SCEVSignExtendExpr *SExt = dyn_cast<SCEVSignExtendExpr>(S)) {
-    ConstantRange X = getUnsignedRange(SExt->getOperand());
-    return setUnsignedRange(SExt,
-      ConservativeResult.intersectWith(X.signExtend(BitWidth)));
+    ConstantRange X = getRange(SExt->getOperand(), SignHint);
+    return setRange(SExt, SignHint,
+                    ConservativeResult.intersectWith(X.signExtend(BitWidth)));
   }
 
   if (const SCEVTruncateExpr *Trunc = dyn_cast<SCEVTruncateExpr>(S)) {
-    ConstantRange X = getUnsignedRange(Trunc->getOperand());
-    return setUnsignedRange(Trunc,
-      ConservativeResult.intersectWith(X.truncate(BitWidth)));
+    ConstantRange X = getRange(Trunc->getOperand(), SignHint);
+    return setRange(Trunc, SignHint,
+                    ConservativeResult.intersectWith(X.truncate(BitWidth)));
   }
 
   if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(S)) {
@@ -3953,143 +3967,6 @@ ScalarEvolution::getUnsignedRange(const SCEV *S) {
             ConservativeResult.intersectWith(
               ConstantRange(C->getValue()->getValue(), APInt(BitWidth, 0)));
 
-    // TODO: non-affine addrec
-    if (AddRec->isAffine()) {
-      Type *Ty = AddRec->getType();
-      const SCEV *MaxBECount = getMaxBackedgeTakenCount(AddRec->getLoop());
-      if (!isa<SCEVCouldNotCompute>(MaxBECount) &&
-          getTypeSizeInBits(MaxBECount->getType()) <= BitWidth) {
-        MaxBECount = getNoopOrZeroExtend(MaxBECount, Ty);
-
-        const SCEV *Start = AddRec->getStart();
-        const SCEV *Step = AddRec->getStepRecurrence(*this);
-
-        ConstantRange StartRange = getUnsignedRange(Start);
-        ConstantRange StepRange = getSignedRange(Step);
-        ConstantRange MaxBECountRange = getUnsignedRange(MaxBECount);
-        ConstantRange EndRange =
-          StartRange.add(MaxBECountRange.multiply(StepRange));
-
-        // Check for overflow. This must be done with ConstantRange arithmetic
-        // because we could be called from within the ScalarEvolution overflow
-        // checking code.
-        ConstantRange ExtStartRange = StartRange.zextOrTrunc(BitWidth*2+1);
-        ConstantRange ExtStepRange = StepRange.sextOrTrunc(BitWidth*2+1);
-        ConstantRange ExtMaxBECountRange =
-          MaxBECountRange.zextOrTrunc(BitWidth*2+1);
-        ConstantRange ExtEndRange = EndRange.zextOrTrunc(BitWidth*2+1);
-        if (ExtStartRange.add(ExtMaxBECountRange.multiply(ExtStepRange)) !=
-            ExtEndRange)
-          return setUnsignedRange(AddRec, ConservativeResult);
-
-        APInt Min = APIntOps::umin(StartRange.getUnsignedMin(),
-                                   EndRange.getUnsignedMin());
-        APInt Max = APIntOps::umax(StartRange.getUnsignedMax(),
-                                   EndRange.getUnsignedMax());
-        if (Min.isMinValue() && Max.isMaxValue())
-          return setUnsignedRange(AddRec, ConservativeResult);
-        return setUnsignedRange(AddRec,
-          ConservativeResult.intersectWith(ConstantRange(Min, Max+1)));
-      }
-    }
-
-    return setUnsignedRange(AddRec, ConservativeResult);
-  }
-
-  if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
-    // Check if the IR explicitly contains !range metadata.
-    Optional<ConstantRange> MDRange = GetRangeFromMetadata(U->getValue());
-    if (MDRange.hasValue())
-      ConservativeResult = ConservativeResult.intersectWith(MDRange.getValue());
-
-    // For a SCEVUnknown, ask ValueTracking.
-    APInt Zeros(BitWidth, 0), Ones(BitWidth, 0);
-    computeKnownBits(U->getValue(), Zeros, Ones, DL, 0, AC, nullptr, DT);
-    if (Ones == ~Zeros + 1)
-      return setUnsignedRange(U, ConservativeResult);
-    return setUnsignedRange(U,
-      ConservativeResult.intersectWith(ConstantRange(Ones, ~Zeros + 1)));
-  }
-
-  return setUnsignedRange(S, ConservativeResult);
-}
-
-/// getSignedRange - Determine the signed range for a particular SCEV.
-///
-ConstantRange
-ScalarEvolution::getSignedRange(const SCEV *S) {
-  // See if we've computed this range already.
-  DenseMap<const SCEV *, ConstantRange>::iterator I = SignedRanges.find(S);
-  if (I != SignedRanges.end())
-    return I->second;
-
-  if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S))
-    return setSignedRange(C, ConstantRange(C->getValue()->getValue()));
-
-  unsigned BitWidth = getTypeSizeInBits(S->getType());
-  ConstantRange ConservativeResult(BitWidth, /*isFullSet=*/true);
-
-  // If the value has known zeros, the maximum signed value will have those
-  // known zeros as well.
-  uint32_t TZ = GetMinTrailingZeros(S);
-  if (TZ != 0)
-    ConservativeResult =
-      ConstantRange(APInt::getSignedMinValue(BitWidth),
-                    APInt::getSignedMaxValue(BitWidth).ashr(TZ).shl(TZ) + 1);
-
-  if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
-    ConstantRange X = getSignedRange(Add->getOperand(0));
-    for (unsigned i = 1, e = Add->getNumOperands(); i != e; ++i)
-      X = X.add(getSignedRange(Add->getOperand(i)));
-    return setSignedRange(Add, ConservativeResult.intersectWith(X));
-  }
-
-  if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) {
-    ConstantRange X = getSignedRange(Mul->getOperand(0));
-    for (unsigned i = 1, e = Mul->getNumOperands(); i != e; ++i)
-      X = X.multiply(getSignedRange(Mul->getOperand(i)));
-    return setSignedRange(Mul, ConservativeResult.intersectWith(X));
-  }
-
-  if (const SCEVSMaxExpr *SMax = dyn_cast<SCEVSMaxExpr>(S)) {
-    ConstantRange X = getSignedRange(SMax->getOperand(0));
-    for (unsigned i = 1, e = SMax->getNumOperands(); i != e; ++i)
-      X = X.smax(getSignedRange(SMax->getOperand(i)));
-    return setSignedRange(SMax, ConservativeResult.intersectWith(X));
-  }
-
-  if (const SCEVUMaxExpr *UMax = dyn_cast<SCEVUMaxExpr>(S)) {
-    ConstantRange X = getSignedRange(UMax->getOperand(0));
-    for (unsigned i = 1, e = UMax->getNumOperands(); i != e; ++i)
-      X = X.umax(getSignedRange(UMax->getOperand(i)));
-    return setSignedRange(UMax, ConservativeResult.intersectWith(X));
-  }
-
-  if (const SCEVUDivExpr *UDiv = dyn_cast<SCEVUDivExpr>(S)) {
-    ConstantRange X = getSignedRange(UDiv->getLHS());
-    ConstantRange Y = getSignedRange(UDiv->getRHS());
-    return setSignedRange(UDiv, ConservativeResult.intersectWith(X.udiv(Y)));
-  }
-
-  if (const SCEVZeroExtendExpr *ZExt = dyn_cast<SCEVZeroExtendExpr>(S)) {
-    ConstantRange X = getSignedRange(ZExt->getOperand());
-    return setSignedRange(ZExt,
-      ConservativeResult.intersectWith(X.zeroExtend(BitWidth)));
-  }
-
-  if (const SCEVSignExtendExpr *SExt = dyn_cast<SCEVSignExtendExpr>(S)) {
-    ConstantRange X = getSignedRange(SExt->getOperand());
-    return setSignedRange(SExt,
-      ConservativeResult.intersectWith(X.signExtend(BitWidth)));
-  }
-
-  if (const SCEVTruncateExpr *Trunc = dyn_cast<SCEVTruncateExpr>(S)) {
-    ConstantRange X = getSignedRange(Trunc->getOperand());
-    return setSignedRange(Trunc,
-      ConservativeResult.intersectWith(X.truncate(BitWidth)));
-  }
-
-  if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(S)) {
     // If there's no signed wrap, and all the operands have the same sign or
     // zero, the value won't ever change sign.
     if (AddRec->getNoWrapFlags(SCEV::FlagNSW)) {
@@ -4115,41 +3992,66 @@ ScalarEvolution::getSignedRange(const SCEV *S) {
       const SCEV *MaxBECount = getMaxBackedgeTakenCount(AddRec->getLoop());
       if (!isa<SCEVCouldNotCompute>(MaxBECount) &&
           getTypeSizeInBits(MaxBECount->getType()) <= BitWidth) {
+
+        // Check for overflow.  This must be done with ConstantRange arithmetic
+        // because we could be called from within the ScalarEvolution overflow
+        // checking code.
+
         MaxBECount = getNoopOrZeroExtend(MaxBECount, Ty);
+        ConstantRange MaxBECountRange = getUnsignedRange(MaxBECount);
+        ConstantRange ZExtMaxBECountRange =
+            MaxBECountRange.zextOrTrunc(BitWidth * 2 + 1);
 
         const SCEV *Start = AddRec->getStart();
         const SCEV *Step = AddRec->getStepRecurrence(*this);
+        ConstantRange StepSRange = getSignedRange(Step);
+        ConstantRange SExtStepSRange = StepSRange.sextOrTrunc(BitWidth * 2 + 1);
+
+        ConstantRange StartURange = getUnsignedRange(Start);
+        ConstantRange EndURange =
+            StartURange.add(MaxBECountRange.multiply(StepSRange));
+
+        // Check for unsigned overflow.
+        ConstantRange ZExtStartURange =
+            StartURange.zextOrTrunc(BitWidth * 2 + 1);
+        ConstantRange ZExtEndURange = EndURange.zextOrTrunc(BitWidth * 2 + 1);
+        if (ZExtStartURange.add(ZExtMaxBECountRange.multiply(SExtStepSRange)) ==
+            ZExtEndURange) {
+          APInt Min = APIntOps::umin(StartURange.getUnsignedMin(),
+                                     EndURange.getUnsignedMin());
+          APInt Max = APIntOps::umax(StartURange.getUnsignedMax(),
+                                     EndURange.getUnsignedMax());
+          bool IsFullRange = Min.isMinValue() && Max.isMaxValue();
+          if (!IsFullRange)
+            ConservativeResult =
+                ConservativeResult.intersectWith(ConstantRange(Min, Max + 1));
+        }
 
-        ConstantRange StartRange = getSignedRange(Start);
-        ConstantRange StepRange = getSignedRange(Step);
-        ConstantRange MaxBECountRange = getUnsignedRange(MaxBECount);
-        ConstantRange EndRange =
-          StartRange.add(MaxBECountRange.multiply(StepRange));
-
-        // Check for overflow. This must be done with ConstantRange arithmetic
-        // because we could be called from within the ScalarEvolution overflow
-        // checking code.
-        ConstantRange ExtStartRange = StartRange.sextOrTrunc(BitWidth*2+1);
-        ConstantRange ExtStepRange = StepRange.sextOrTrunc(BitWidth*2+1);
-        ConstantRange ExtMaxBECountRange =
-          MaxBECountRange.zextOrTrunc(BitWidth*2+1);
-        ConstantRange ExtEndRange = EndRange.sextOrTrunc(BitWidth*2+1);
-        if (ExtStartRange.add(ExtMaxBECountRange.multiply(ExtStepRange)) !=
-            ExtEndRange)
-          return setSignedRange(AddRec, ConservativeResult);
-
-        APInt Min = APIntOps::smin(StartRange.getSignedMin(),
-                                   EndRange.getSignedMin());
-        APInt Max = APIntOps::smax(StartRange.getSignedMax(),
-                                   EndRange.getSignedMax());
-        if (Min.isMinSignedValue() && Max.isMaxSignedValue())
-          return setSignedRange(AddRec, ConservativeResult);
-        return setSignedRange(AddRec,
-          ConservativeResult.intersectWith(ConstantRange(Min, Max+1)));
+        ConstantRange StartSRange = getSignedRange(Start);
+        ConstantRange EndSRange =
+            StartSRange.add(MaxBECountRange.multiply(StepSRange));
+
+        // Check for signed overflow. This must be done with ConstantRange
+        // arithmetic because we could be called from within the ScalarEvolution
+        // overflow checking code.
+        ConstantRange SExtStartSRange =
+            StartSRange.sextOrTrunc(BitWidth * 2 + 1);
+        ConstantRange SExtEndSRange = EndSRange.sextOrTrunc(BitWidth * 2 + 1);
+        if (SExtStartSRange.add(ZExtMaxBECountRange.multiply(SExtStepSRange)) ==
+            SExtEndSRange) {
+          APInt Min = APIntOps::smin(StartSRange.getSignedMin(),
+                                     EndSRange.getSignedMin());
+          APInt Max = APIntOps::smax(StartSRange.getSignedMax(),
+                                     EndSRange.getSignedMax());
+          bool IsFullRange = Min.isMinSignedValue() && Max.isMaxSignedValue();
+          if (!IsFullRange)
+            ConservativeResult =
+                ConservativeResult.intersectWith(ConstantRange(Min, Max + 1));
+        }
       }
     }
 
-    return setSignedRange(AddRec, ConservativeResult);
+    return setRange(AddRec, SignHint, ConservativeResult);
   }
 
   if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
@@ -4158,18 +4060,33 @@ ScalarEvolution::getSignedRange(const SCEV *S) {
     if (MDRange.hasValue())
       ConservativeResult = ConservativeResult.intersectWith(MDRange.getValue());
 
-    // For a SCEVUnknown, ask ValueTracking.
-    if (!U->getValue()->getType()->isIntegerTy() && !DL)
-      return setSignedRange(U, ConservativeResult);
-    unsigned NS = ComputeNumSignBits(U->getValue(), DL, 0, AC, nullptr, DT);
-    if (NS <= 1)
-      return setSignedRange(U, ConservativeResult);
-    return setSignedRange(U, ConservativeResult.intersectWith(
-      ConstantRange(APInt::getSignedMinValue(BitWidth).ashr(NS - 1),
-                    APInt::getSignedMaxValue(BitWidth).ashr(NS - 1)+1)));
+    // Split here to avoid paying the compile-time cost of calling both
+    // computeKnownBits and ComputeNumSignBits.  This restriction can be lifted
+    // if needed.
+
+    if (SignHint == ScalarEvolution::HINT_RANGE_UNSIGNED) {
+      // For a SCEVUnknown, ask ValueTracking.
+      APInt Zeros(BitWidth, 0), Ones(BitWidth, 0);
+      computeKnownBits(U->getValue(), Zeros, Ones, DL, 0, AC, nullptr, DT);
+      if (Ones != ~Zeros + 1)
+        ConservativeResult =
+            ConservativeResult.intersectWith(ConstantRange(Ones, ~Zeros + 1));
+    } else {
+      assert(SignHint == ScalarEvolution::HINT_RANGE_SIGNED &&
+             "generalize as needed!");
+      if (U->getValue()->getType()->isIntegerTy() || DL) {
+        unsigned NS = ComputeNumSignBits(U->getValue(), DL, 0, AC, nullptr, DT);
+        if (NS > 1)
+          ConservativeResult = ConservativeResult.intersectWith(ConstantRange(
+              APInt::getSignedMinValue(BitWidth).ashr(NS - 1),
+              APInt::getSignedMaxValue(BitWidth).ashr(NS - 1) + 1));
+      }
+    }
+
+    return setRange(U, SignHint, ConservativeResult);
   }
 
-  return setSignedRange(S, ConservativeResult);
+  return setRange(S, SignHint, ConservativeResult);
 }
 
 /// createSCEV - We know that there is no SCEV for the specified value.
diff --git a/llvm/test/Analysis/ScalarEvolution/range-signedness.ll b/llvm/test/Analysis/ScalarEvolution/range-signedness.ll
new file mode 100644
index 00000000000..d04fc9eb56b
--- /dev/null
+++ b/llvm/test/Analysis/ScalarEvolution/range-signedness.ll
@@ -0,0 +1,39 @@
+; RUN: opt -analyze -scalar-evolution < %s | FileCheck %s
+
+define void @x(i1* %cond) {
+; CHECK-LABEL: Classifying expressions for: @x
+ entry:
+  br label %loop
+
+ loop:
+  %idx = phi i8 [ 0, %entry ], [ %idx.inc, %loop ]
+; CHECK: %idx = phi i8 [ 0, %entry ], [ %idx.inc, %loop ]
+; CHECK-NEXT:  -->  {0,+,1}<nuw><nsw><%loop> U: [0,-128) S: [0,-128)
+
+  %idx.inc = add nsw i8 %idx, 1
+
+  %c = load volatile i1, i1* %cond
+  br i1 %c, label %loop, label %exit
+
+ exit:
+  ret void
+}
+
+define void @y(i8* %addr) {
+; CHECK-LABEL: Classifying expressions for: @y
+ entry:
+  br label %loop
+
+ loop:
+  %idx = phi i8 [-5, %entry ], [ %idx.inc, %loop ]
+; CHECK:   %idx = phi i8 [ -5, %entry ], [ %idx.inc, %loop ]
+; CHECK-NEXT:  -->  {-5,+,1}<%loop> U: [-5,6) S: [-5,6)
+
+  %idx.inc = add i8 %idx, 1
+
+  %continue = icmp slt i8 %idx.inc, 6
+  br i1 %continue, label %loop, label %exit
+
+ exit:
+  ret void
+}