[PATCH] D20349: Fix a clang bug in lambda capture of 'this'

[Faisal Vali via cfe-commits]

Thanks for the work here - but this bug is a duplicate of this:
https://llvm.org/bugs/show_bug.cgi?id=27507, which unearthed some
other subtle bugs with the cv capture of *this by copy.
I've submitted a patch for review here: http://reviews.llvm.org/D19783
that addresses both issues - about 2-3 weeks ago -  given the
nastiness of this bug, the fact that it was introduced by one of my
patches and that there is now a second report of the bug - and that I
feel reasonably good about the fix - I'll commit this patch before the
weekend, unless Richard raises an issue.


Faisal Vali



On Tue, May 17, 2016 at 11:23 PM, Taewook Oh <twoh at fb.com> wrote:
> twoh created this revision.
> twoh added reviewers: faisalv, rsmith.
> twoh added a subscriber: cfe-commits.
>
> (This is a fix for Bug 27797 https://llvm.org/bugs/show_bug.cgi?id=27797).
>
> Currently when RebuildLambdaScopeInfo() function in lib/Sema/SemaDecl.cpp observes lambda capturing 'this', it calls Sema::getCurrentThisType() to get the type of 'this'. However, clang (revision 269789) crashes with an assertion failure inside Sema::getCurrentThisType() if template instantiation creates nested lambdas. Inside, Sema::getCurrentThisType(), there is an assertion saying that getCurLambda() never returns nullptr, but nest lambdas created by template instantiation makes getCurLambda() returns nullptr.
>
> Actually, even without the assertion failure, calling Sema::getCurrentThisType() from RebuildLambdaScopeInfo() seems wrong. When there are nested lambdas, what is required from Sema::getCurrentThisType() is a type of 'this' for nesting lambda, while what is supposed to be returned from Sema::getCurrentThisType() is a type of 'this' for nested lambda.
>
> This patch addresses this issue and makes RebuildLambdaScopeInfo() compute the correct 'this' type.
>
> http://reviews.llvm.org/D20349
>
> Files:
>   lib/Sema/SemaDecl.cpp
>
> Index: lib/Sema/SemaDecl.cpp
> ===================================================================
> --- lib/Sema/SemaDecl.cpp
> +++ lib/Sema/SemaDecl.cpp
> @@ -11109,8 +11109,16 @@
>            CaptureType, /*Expr*/ nullptr);
>
>      } else if (C.capturesThis()) {
> +      QualType ThisTy = CallOperator->getThisType(S.Context);
> +      QualType BaseTy = ThisTy->getPointeeType();
> +      if (C.getCaptureKind() == LCK_StarThis &&
> +          CallOperator->isConst() &&
> +          !BaseTy.isConstQualified()) {
> +        BaseTy.addConst();
> +        ThisTy = S.Context.getPointerType(BaseTy);
> +      }
>        LSI->addThisCapture(/*Nested*/ false, C.getLocation(),
> -                              S.getCurrentThisType(), /*Expr*/ nullptr,
> +                              ThisTy, /*Expr*/ nullptr,
>                                C.getCaptureKind() == LCK_StarThis);
>      } else {
>        LSI->addVLATypeCapture(C.getLocation(), I->getType());
>
>