Address review comments

Author: usha1830

llvm/lib/CodeGen/GlobalISel/GISelValueTracking.cpp

@@ -1961,13 +1961,13 @@ unsigned GISelValueTracking::computeNumSignBits(Register R,
   case TargetOpcode::G_CONCAT_VECTORS: {
     if (MRI.getType(MI.getOperand(0).getReg()).isScalableVector())
       break;
-    FirstAnswer = std::numeric_limits<unsigned>::max();
+    FirstAnswer = TyBits;
     // Determine the minimum number of sign bits across all demanded
     // elts of the input vectors. Early out if the result is already 1.
     unsigned NumSubVectorElts =
         MRI.getType(MI.getOperand(1).getReg()).getNumElements();
     unsigned NumSubVectors = MI.getNumOperands() - 1;
-    for (unsigned i = 0; (i < NumSubVectors); ++i) {
+    for (unsigned i = 0; i < NumSubVectors; ++i) {
       APInt DemandedSub =
           DemandedElts.extractBits(NumSubVectorElts, i * NumSubVectorElts);
       if (!DemandedSub)
@@ -1976,6 +1976,10 @@ unsigned GISelValueTracking::computeNumSignBits(Register R,
                                          DemandedSub, Depth + 1);
 
       FirstAnswer = std::min(FirstAnswer, Tmp2);
+
+      // If we don't know any bits, early out.
+      if (FirstAnswer == 1)
+        break;
     }
     break;
   }