[LoopUnroll] Move a simple check earlier. NFC.

[haicheng]

Summary

CallInst can have side effects. Move the check of CallInst earlier to skip AddCostRecursively.

[mcrosier]

LGTM.

llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp

for (unsigned Idx = 0; Idx != BBWorklist.size(); ++Idx) {
                                            (unsigned)IsFree,
                                            /*IsCounted*/ false}).second;
         (void)Inserted;
         assert(Inserted && "Cannot have a state for an unvisited instruction!");
 
         if (IsFree)
           continue;
 
-        // If the instruction might have a side-effect recursively account for
-        // the cost of it and all the instructions leading up to it.
-        if (I.mayHaveSideEffects())
-          AddCostRecursively(I, Iteration);
-
         // Can't properly model a cost of a call.
         // FIXME: With a proper cost model we should be able to do it.
         if(isa<CallInst>(&I))
           return None;
 
+        // If the instruction might have a side-effect recursively account for
+        // the cost of it and all the instructions leading up to it.
+        if (I.mayHaveSideEffects())
+          AddCostRecursively(I, Iteration);
+
         // If unrolled body turns out to be too big, bail out.
         if (UnrolledCost > MaxUnrolledLoopSize) {
           DEBUG(dbgs() << "  Exceeded threshold.. exiting.\n"
                        << "  UnrolledCost: " << UnrolledCost
                        << ", MaxUnrolledLoopSize: " << MaxUnrolledLoopSize
                        << "\n");
           return None;
         }