[SelectionDAG] Use APInt::zextOrSelf instead of zextOrTrunc in ComputePHILiveOutRegInfo

The width never decreases here.

Author: topperc

llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp

@@ -459,7 +459,7 @@ void FunctionLoweringInfo::ComputePHILiveOutRegInfo(const PHINode *PN) {
   }
 
   if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
-    APInt Val = CI->getValue().zextOrTrunc(BitWidth);
+    APInt Val = CI->getValue().zextOrSelf(BitWidth);
     DestLOI.NumSignBits = Val.getNumSignBits();
     DestLOI.Known = KnownBits::makeConstant(Val);
   } else {
@@ -491,7 +491,7 @@ void FunctionLoweringInfo::ComputePHILiveOutRegInfo(const PHINode *PN) {
     }
 
     if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
-      APInt Val = CI->getValue().zextOrTrunc(BitWidth);
+      APInt Val = CI->getValue().zextOrSelf(BitWidth);
       DestLOI.NumSignBits = std::min(DestLOI.NumSignBits, Val.getNumSignBits());
       DestLOI.Known.Zero &= ~Val;
       DestLOI.Known.One &= Val;