[InstCombine] Avoid uses of ConstantExpr::getLShr()

Use the constant folding API instead.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -2132,9 +2132,12 @@ static bool collectInsertionElements(Value *V, unsigned Shift,
     Type *ElementIntTy = IntegerType::get(C->getContext(), ElementSize);
 
     for (unsigned i = 0; i != NumElts; ++i) {
-      unsigned ShiftI = Shift+i*ElementSize;
-      Constant *Piece = ConstantExpr::getLShr(C, ConstantInt::get(C->getType(),
-                                                                  ShiftI));
+      unsigned ShiftI = Shift + i * ElementSize;
+      Constant *Piece = ConstantFoldBinaryInstruction(
+          Instruction::LShr, C, ConstantInt::get(C->getType(), ShiftI));
+      if (!Piece)
+        return false;
+
       Piece = ConstantExpr::getTrunc(Piece, ElementIntTy);
       if (!collectInsertionElements(Piece, ShiftI, Elements, VecEltTy,
                                     isBigEndian))

llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp

@@ -299,8 +299,10 @@ dropRedundantMaskingOfLeftShiftInput(BinaryOperator *OuterShift,
 
     // And compute the mask as usual: (-1 l>> (NumHighBitsToClear))
     auto *ExtendedAllOnes = ConstantExpr::getAllOnesValue(ExtendedTy);
-    NewMask =
-        ConstantExpr::getLShr(ExtendedAllOnes, ExtendedNumHighBitsToClear);
+    NewMask = ConstantFoldBinaryOpOperands(Instruction::LShr, ExtendedAllOnes,
+                                           ExtendedNumHighBitsToClear, Q.DL);
+    if (!NewMask)
+      return nullptr;
   } else
     return nullptr; // Don't know anything about this pattern.