[InstCombine] Added check for NUW flag.

[IlyaKrotov]

Summary

Check if we can add NUW flag. If so, set this.

[sanjoy]

As I was looking through this, I realized that the nsw case is incorrect: http://reviews.llvm.org/D9629

InstructionCombining.cpp

if (B == D || (InnerCommutative && B == C)) {
         SimplifiedInst = Builder->CreateBinOp(InnerOpcode, V, B);
       }
     }
 
   if (SimplifiedInst) {
     ++NumFactor;
     SimplifiedInst->takeName(&I);
 
-    // Check if we can add NSW flag to SimplifiedInst. If so, set NSW flag.
-    // TODO: Check for NUW.
+    // Check if we can add NSW/NUW flag to SimplifiedInst. If so, set NSW/NUW flag.
     if (BinaryOperator *BO = dyn_cast<BinaryOperator>(SimplifiedInst)) {
       if (isa<OverflowingBinaryOperator>(SimplifiedInst)) {
         bool HasNSW = false;
-        if (isa<OverflowingBinaryOperator>(&I))
+        bool HasNUW = false;
+        if (isa<OverflowingBinaryOperator>(&I)){
           HasNSW = I.hasNoSignedWrap();
-
+          HasNUW = I.hasNoUnsignedWrap();
+        }
         if (BinaryOperator *Op0 = dyn_cast<BinaryOperator>(LHS))
-          if (isa<OverflowingBinaryOperator>(Op0))
+          if (isa<OverflowingBinaryOperator>(Op0)){
             HasNSW &= Op0->hasNoSignedWrap();
-
+            HasNUW &= Op0->hasNoUnsignedWrap();
+          }
         if (BinaryOperator *Op1 = dyn_cast<BinaryOperator>(RHS))
-          if (isa<OverflowingBinaryOperator>(Op1))
+          if (isa<OverflowingBinaryOperator>(Op1)){
             HasNSW &= Op1->hasNoSignedWrap();
+            HasNUW &= Op1->hasNoUnsignedWrap();
+          }
         BO->setHasNoSignedWrap(HasNSW);
+        BO->setHasNoUnsignedWrap(HasNUW);
       }
     }
   }
   return SimplifiedInst;
 }
 
 /// SimplifyUsingDistributiveLaws - This tries to simplify binary operations
 /// which some other binary operation distributes over either by factorizing