Replace expression with macro using clang AST

I am looking to change the following code, with the help of the clang ast matcher.

foo(NUM << DEV_SHIFT | DEVICE);

to

foo(ADDR(NUM, DEVICE));

with

#define ADDR(a, b) (((a) << NUM_SHIFT) | (b))

I have the following AST-matcher that seems to identify the code pretty well.

Finder->addMatcher(
       callExpr(hasArgument(                                                                                                                                                             
           0, binaryOperator(hasOperatorName("|"),
                             hasLHS(ignoringParenImpCasts(
                                 binaryOperator(hasOperatorName("<<")))))
                  .bind("replaceWithMacro"))),
       this);

But I have a problem to understand how to write the check and the translation. I am currently stuck with this code:

void FirstCheckCheck::check(const MatchFinder::MatchResult &Result) {
  // FIXME: Add callback implementation.
  if (const auto MatchedDecl =
          Result.Nodes.getNodeAs<CallExpr>("replaceWithMacro")) {
    diag(MatchedDecl->getExprLoc(), "CallExp");
  } else if (const auto MatchedDecl =
                 Result.Nodes.getNodeAs<Expr>("replaceWithMacro")) {
    diag(MatchedDecl->getExprLoc(), "Expr");
    diag(MatchedDecl->getBeginLoc(), "BeginLOC");
    diag(MatchedDecl->getEndLoc(), "EndLOC");
  }

I don't know how to extract the two variables as strings. I was looking at the documentation for the Expr class (http://clang.llvm.org/doxygen/classclang_1_1Expr.html), but I couldn't find something useful.

If somebody could point me into the right direction it would be appreciated.

Add edit's.

This is the solution that I am quite happy with. It is based on boq's suggestion from the comments.

//===--- FirstCheckCheck.cpp - clang-tidy ---------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "FirstCheckCheck.h"
#include "clang/AST/ASTContext.h"
#include "clang/ASTMatchers/ASTMatchFinder.h"

using namespace clang::ast_matchers;

namespace clang {
namespace tidy {
namespace misc {

void FirstCheckCheck::registerMatchers(MatchFinder *Finder) {
  // FIXME: Add matchers.
  //
  Finder->addMatcher(
      callExpr(hasArgument(
          1,
          binaryOperator(
              hasOperatorName("|"),
              hasRHS(ignoringImplicit(
                  anyOf(declRefExpr().bind("moduleNum"), integerLiteral().bind(
                      "moduleNum")))),
              hasLHS(ignoringParens(
                  binaryOperator(hasOperatorName("<<"),
                                 hasLHS(ignoringImplicit(anyOf(
                                     declRefExpr().bind("deviceNum"),
                                     integerLiteral().bind("deviceNum"))))))))
              .bind("replaceWithMacro"))),
      this);
}

void FirstCheckCheck::check(const MatchFinder::MatchResult &Result) {
  // FIXME: Add callback implementation.
    std::string deviceNumString;
    std::string moduleNumString;
    std::string ReplacementText;

  if (const auto MatchedDecl =
          Result.Nodes.getNodeAs<Expr>("deviceNum")) {

    const LangOptions &Opts = getLangOpts();

    /* get device string */
    deviceNumString = Lexer::getSourceText(
        CharSourceRange::getTokenRange(MatchedDecl->getSourceRange()),
        *Result.SourceManager, Opts);
  }
  /* ((uint16_t)(deviceNum << 8 | moduleNum)) */
  if (const auto MatchedDecl =
          Result.Nodes.getNodeAs<Expr>("moduleNum")) {

    const LangOptions &Opts = getLangOpts();

    moduleNumString = Lexer::getSourceText(
        CharSourceRange::getTokenRange(MatchedDecl->getSourceRange()),
        *Result.SourceManager, Opts);
  }
  if (const auto MatchedDecl =
                 Result.Nodes.getNodeAs<Expr>("replaceWithMacro")) {
    const LangOptions &Opts = getLangOpts();

    ReplacementText = Lexer::getSourceText(
        CharSourceRange::getTokenRange(MatchedDecl->getSourceRange()),
        *Result.SourceManager, Opts);

    std::string replacementString =
        "ADDR(" + deviceNumString + ", " + moduleNumString + ")";

    FixItHint Hint = FixItHint::CreateReplacement(
        MatchedDecl->getSourceRange(), replacementString);

    diag(MatchedDecl->getBeginLoc(), "Replace with ADDR() macro") << Hint;
  }

  /* diag(MatchedDecl->getLocation(), "insert 'awesome'", DiagnosticIDs::Note)
   */
  /*     << FixItHint::CreateInsertion(MatchedDecl->getLocation(), "awesome_");
   */
}

} // namespace misc
} // namespace tidy
} // namespace clang