// sure that we don't end up doing O(n^2) work
	// for a chain of n copies.
	for v != w {
		x := v.Args[0]
		v.SetArg(0, w)
		v = x
	}
	return w
}

// copyelimValue ensures that no args of v are copies.
func copyelimValue(v *Value) {
	for i, a := range v.Args {
		if a.Op == OpCopy {
			v.SetArg(i, copySource(a))
		}
	}
}

// phielim eliminates redundant phi values from f.

LogicalResult QuantizedConstRewrite::matchAndRewrite(
    QuantizeCastOp qbarrier, PatternRewriter &rewriter) const {
  Attribute value;

  // Is the operand a constant?
  if (!matchPattern(qbarrier.getArg(), m_Constant(&value))) {
    return failure();
  }

  // Does the qbarrier convert to a quantized type. This will not be true
  // if a quantized type has not yet been chosen or if the cast to an equivalent

  // Matches x -> [scast -> scast] -> y, replacing the second scast with the
  // value of x if the casts invert each other.
  auto srcScastOp = getArg().getDefiningOp<StorageCastOp>();
  if (!srcScastOp || srcScastOp.getArg().getType() != getType())
    return OpFoldResult();
  return srcScastOp.getArg();
}

/// The quantization specification should match the expressed type.

  // Matches x -> [scast -> scast] -> y, replacing the second scast with the
  // value of x if the casts invert each other.
  auto srcScastOp = getArg().getDefiningOp<StorageCastOp>();
  if (!srcScastOp || srcScastOp.getArg().getType() != getType())
    return OpFoldResult();
  return srcScastOp.getArg();
}

/// The quantization specification should match the expressed type.

    b.setInsertionPoint(op);
    if (auto dq = llvm::dyn_cast<quantfork::DequantizeCastOp>(op)) {
      auto dcast = b.create<DequantizeOp>(dq.getLoc(), dq.getResult().getType(),
                                          dq.getArg());
      dq.getResult().replaceAllUsesWith(dcast);
      if (auto extra_attr = op->getAttr(mlir::quant::kVolatileOpAttrName)) {
        dcast->setAttr(mlir::quant::kVolatileOpAttrName, extra_attr);
      }
      dq.erase();