1 files changed, 16 insertions, 0 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index bda8cea4e41f..6e727ce6e35c 100644
--- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -684,6 +684,10 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     break;
   case Instruction::SRem:
     if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
+      // X % -1 demands all the bits because we don't want to introduce
+      // INT_MIN % -1 (== undef) by accident.
+      if (Rem->isAllOnesValue())
+        break;
       APInt RA = Rem->getValue().abs();
       if (RA.isPowerOf2()) {
         if (DemandedMask.ult(RA))    // srem won't affect demanded bits
@@ -712,6 +716,18 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
         assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?"); 
       }
     }
+
+    // The sign bit is the LHS's sign bit, except when the result of the
+    // remainder is zero.
+    if (DemandedMask.isNegative() && KnownZero.isNonNegative()) {
+      APInt Mask2 = APInt::getSignBit(BitWidth);
+      APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
+      ComputeMaskedBits(I->getOperand(0), Mask2, LHSKnownZero, LHSKnownOne,
+                        Depth+1);
+      // If it's known zero, our sign bit is also zero.
+      if (LHSKnownZero.isNegative())
+        KnownZero |= LHSKnownZero;
+    }
     break;
   case Instruction::URem: {
     APInt KnownZero2(BitWidth, 0), KnownOne2(BitWidth, 0);