+/// SimplifySelectInst - Given operands for a SelectInst, see if we can fold
+/// the result. If not, this returns null.
+Value *llvm::SimplifySelectInst(Value *CondVal, Value *TrueVal, Value *FalseVal,
+ const TargetData *TD) {
+ // select true, X, Y -> X
+ // select false, X, Y -> Y
+ if (ConstantInt *CB = dyn_cast<ConstantInt>(CondVal))
+ return CB->getZExtValue() ? TrueVal : FalseVal;
+
+ // select C, X, X -> X
+ if (TrueVal == FalseVal)
+ return TrueVal;
+
+ if (isa<UndefValue>(TrueVal)) // select C, undef, X -> X
+ return FalseVal;
+ if (isa<UndefValue>(FalseVal)) // select C, X, undef -> X
+ return TrueVal;
+ if (isa<UndefValue>(CondVal)) { // select undef, X, Y -> X or Y
+ if (isa<Constant>(TrueVal))
+ return TrueVal;
+ return FalseVal;
+ }
+
+
+
+ return 0;
+}
+
+