[cfe-dev] ASTMatcher for assert()

[Manuel Klimek]

On Fri, Jun 6, 2014 at 6:04 PM, Alex Horn <alex.horn at cs.ox.ac.uk> wrote:

> > [W]hat's the problem rewriting this inside the macro?
>
> The problem I encountered was that Clang would not automatically
> invoke the ASTMatchers inside the macro definitions. The comments I
> found before I posted on this mailing list indicated that this is by
> design and that it can only be circumvented by rewriting macros
> beforehand, i.e. -rewrite-macros. But your previous remark gives me
> hope that the situation might have changed, or that I have just missed
> the right mailing list comments.
>

Well, the macro has to be actually used ;) Even if it's a library, I'd hope
you have at least a test that uses the macro... (same for templates btw).


>
> > [Use PPCallbacks to] collect information about the macros, and then use
> that information to generate the replacements.
>
> I'm afraid that with my limited expertise in Clang I would have to
> look at an example that illustrates the technique you've in mind. It
> may be even that I have not articulated clearly enough and that we are
> thinking of two different things here.
>

I'm, not sure you need that kind of information. See above. Code that is in
macros will be visited at every expansion location.


>
> On 6 June 2014 16:24, Manuel Klimek <klimek at google.com> wrote:
> > On Fri, Jun 6, 2014 at 4:48 PM, Alex Horn <alex.horn at cs.ox.ac.uk> wrote:
> >>
> >> > [...] Why not write all tools to work on the non-macro-rewritten code?
> >> > (you can get  macros yourself via the PPCallbacks interface).
> >>
> >> As far as I understand, PPCallbacks operate on a different level of
> >> abstraction than ASTMatchers. The RefactoringTool I have in mind
> >> rewrites two things: (1) "assert()" macros and (2) control-flow
> >> conditions in "if-then-else", "while" and "for" statements. The
> >> rewriting of both (1) and (2) is now implemented as ASTMatchers.
> >> Unfortunately, (2) does not work correctly unless macros are rewritten
> >> beforehand. To see this, consider "#define compare(a, b) do { if ((a)
> >> < (b)) swap(a, b) } while(0);".
> >
> >
> > I'm considering it :) So what's the problem rewriting this inside the
> macro?
> >
> >>
> >> I presumed for now that it does not make sense, generally speaking, to
> >> invoke ASTMatchers from within PPCallbacks because the source code
> >> inside a macro definition may not be well-formed. This is why I was
> >> merely looking for a way to combine ASTMatchers and cc1 drivers.
> >
> >
> > No, my idea on how to use PPCallbacks was to just use them to collect
> > information about the macros, and then use that information to generate
> the
> > replacements.
> >
> >>
> >>
> >> Best,
> >> Alex
> >>
> >> On 6 June 2014 15:13, Manuel Klimek <klimek at google.com> wrote:
> >> > On Fri, Jun 6, 2014 at 4:10 PM, Alex Horn <alex.horn at cs.ox.ac.uk>
> wrote:
> >> >>
> >> >> Thanks for the effective response. This helped on the right track and
> >> >> I've successfully used SourceManager::getImmediateExpansionRange() to
> >> >> insert BAR and its surrounding parenthesis correctly.
> >> >>
> >> >> As a directly related issue: The proposed technique of using the
> >> >> expansion range does the trick but of course requires that "-cc1
> >> >> -rewrite-macros" is _not_ invoked prior to rewriting "assert()"
> >> >> macros. However, this is problematic when other rewrites in the same
> >> >> RefactoringTool _do_ rely on macros having been rewritten. This poses
> >> >> the question whether these things can coexist in the same
> >> >> RefactoringTool. In particular, is it possible to call the
> >> >> RewriteMacros functionality only after certain matches have
> completed?
> >> >>
> >> >> To ask the same thing differently, what is the preferred way to
> >> >> compose ASTMatchers and cc1 drivers such as RewriteMacros?
> >> >
> >> >
> >> > I wouldn't combine them. Why not write all tools to work on the
> >> > non-macro-rewritten code? (you can get macros yourself via the
> >> > PPCallbacks
> >> > interface).
> >> >
> >> >>
> >> >>
> >> >> On 6 June 2014 13:56, Manuel Klimek <klimek at google.com> wrote:
> >> >> > On Tue, Jun 3, 2014 at 5:36 PM, Alex Horn <alex.horn at cs.ox.ac.uk>
> >> >> > wrote:
> >> >> >>
> >> >> >> Hello,
> >> >> >>
> >> >> >> I am struggling to replace "assert(c)" macro calls by "BAR(c)"
> where
> >> >> >> c
> >> >> >> is some integer expression and BAR is a function.
> >> >> >>
> >> >> >> The problem manifests itself in
> >> >> >> RefactoringTool::applyAllReplacements
> >> >> >> which returns false, thereby causing the tool to skip
> replacements.
> >> >> >>
> >> >> >> I am using the following ASTMatcher:
> >> >> >>
> >> >> >> StatementMatcher makeAssertMatcher() {
> >> >> >>   return
> >> >> >>
> >> >> >>
> >> >> >>
> callExpr(callee(functionDecl(hasName("__builtin_expect")))).bind("AssertBindId");
> >> >> >> }
> >> >> >>
> >> >> >> Note: callExpr(callee(functionDecl(hasName("assert"))) won't work
> >> >> >> here
> >> >> >> because assert() is a macro according to the assert.h and cassert
> >> >> >> headers.
> >> >> >>
> >> >> >> Here's an example match using clang-query:
> >> >> >>
> >> >> >> example.cpp:
> >> >> >>
> >> >> >>   #include <assert.h>
> >> >> >>   int main() {
> >> >> >>     assert(false);
> >> >> >>     return 0;
> >> >> >>   }
> >> >> >>
> >> >> >> $ clang-query> match
> >> >> >> callExpr(callee(functionDecl(hasName("__builtin_expect"))))
> >> >> >>
> >> >> >>   Match #1:
> >> >> >>
> >> >> >>   example.cpp:4:3: note: "AssertBindId" binds here
> >> >> >>     assert(false);
> >> >> >>     ^~~~~~~~~~~~~
> >> >> >>   /usr/include/assert.h:93:6: note: expanded from macro 'assert'
> >> >> >>       (__builtin_expect(!(e), 0) ? __assert_rtn(__func__,
> __FILE__,
> >> >> >> __LINE__, #e) : (void)0)
> >> >> >>        ^~~~~~~~~~~~~~~~~~~~~~~~~
> >> >> >>   1 match.
> >> >> >>
> >> >> >> But I cannot find the correct way to rewrite the match; the
> >> >> >> following
> >> >> >> replacement is skipped (i.e. see line 295 in Refactoring.cpp):
> >> >> >>
> >> >> >>   const CallExpr *E =
> >> >> >> Result.Nodes.getNodeAs<CallExpr>("AssertBindId");
> >> >> >>   SourceManager &SM = *Result.SourceManager;
> >> >> >>   SourceLocation LocBegin = E->getLocStart();
> >> >> >>   Replace->insert(tooling::Replacement(SM, LocBegin,
> >> >> >>     /* number of letters in assert */ 6, "BAR"));
> >> >> >>
> >> >> >> What is the correct way (if any) to rewrite call expressions of
> >> >> >> macros
> >> >> >> such as "assert()"?
> >> >> >
> >> >> >
> >> >> > You need to get the expansion location:
> >> >> > SourceLocation ExpLocBegin = SM.getExpansionLoc(LocBegin);
> >> >> > Replace->insert(tooling::Replacement(SM, ExpLocBegin, 6, "BAR"));
> >> >> >
> >> >> > Something like this should do the trick...
> >> >> > Cheers,
> >> >> > /Manuel
> >> >
> >> >
> >
> >
>
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