Replace expression with macro using clang AST

Question

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.

Always put parentheses around the macro argument names in the expansion (when dealing with arithmetic or logical expressions). Hence: `#define ADDR(a, b) (((a) << NUM_SHIFT) | (b))`. It probably isn't a factor in your problem, but it is basic C code hygiene. (There are exceptions to the rule, such as when dealing with strings, but keep to the guideline when sensible — and this is one place where it would be sensible.) — Jonathan Leffler, May 06 '19 at 23:50
Seems to me you are trying to extract the two variables from the Expr.. Why not add two additional bindings? you already worked out the matcher, just modify a bit to bind the left side of "<<" (NUM) and the right side of "|" (DEVICE). Then you can get the exact location of the two variables names to create the replacement string. — Booo, May 09 '19 at 18:47

score 0 · Accepted Answer · answered May 28 '19 at 12:31

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

Replace expression with macro using clang AST

1 Answers1