I have a patch I put together a while back as an attempt to fix a different bug, that creates a new CastKind for this operation (didn't work out there, but it might do so here). I'll dig it out and mail it to you in case it's a useful starting point.
On Fri, 14 Dec 2018 at 14:42, Keane, Erich via cfe-commits < cfe-commits@lists.llvm.org> wrote: > Alright, no problem. I’ll push a revert in a few minutes and give it > another try. Perhaps I can suppress the creation of a CK_LValueToRValue in > the case where it’s a read from nullptr_t > > > > > > *From:* Richard Smith [mailto:rich...@metafoo.co.uk] > *Sent:* Friday, December 14, 2018 2:41 PM > *To:* Keane, Erich <erich.ke...@intel.com> > *Cc:* cfe-commits <cfe-commits@lists.llvm.org> > *Subject:* Re: r349201 - Add extension to always default-initialize > nullptr_t. > > > > Sorry, I was late with my review comment. I think this is the wrong way to > approach this problem. This does not "fix all situations where nullptr_t > would seem uninitialized", and it makes our AST representation lose source > fidelity. > > > > On Fri, 14 Dec 2018 at 14:25, Erich Keane via cfe-commits < > cfe-commits@lists.llvm.org> wrote: > > Author: erichkeane > Date: Fri Dec 14 14:22:29 2018 > New Revision: 349201 > > URL: http://llvm.org/viewvc/llvm-project?rev=349201&view=rev > Log: > Add extension to always default-initialize nullptr_t. > > Core issue 1013 suggests that having an uninitialied std::nullptr_t be > UB is a bit foolish, since there is only a single valid value. This DR > reports that DR616 fixes it, which does so by making lvalue-to-rvalue > conversions from nullptr_t be equal to nullptr. > > However, just implementing that results in warnings/etc in many places. > In order to fix all situations where nullptr_t would seem uninitialized, > this patch instead (as an otherwise transparent extension) default > initializes uninitialized VarDecls of nullptr_t. > > Differential Revision: https://reviews.llvm.org/D53713 > > Change-Id: I84d72a9290054fa55341e8cbdac43c8e7f25b885 > > Added: > cfe/trunk/test/SemaCXX/nullptr_t-init.cpp (with props) > Modified: > cfe/trunk/lib/Sema/SemaInit.cpp > cfe/trunk/test/Analysis/nullptr.cpp > cfe/trunk/test/SemaCXX/ast-print-crash.cpp > > Modified: cfe/trunk/lib/Sema/SemaInit.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaInit.cpp?rev=349201&r1=349200&r2=349201&view=diff > > ============================================================================== > --- cfe/trunk/lib/Sema/SemaInit.cpp (original) > +++ cfe/trunk/lib/Sema/SemaInit.cpp Fri Dec 14 14:22:29 2018 > @@ -4881,6 +4881,13 @@ static void TryDefaultInitialization(Sem > return; > } > > + // As an extension, and to fix Core issue 1013, zero initialize > nullptr_t. > + // Since there is only 1 valid value of nullptr_t, we can just use that. > + if (DestType->isNullPtrType()) { > + Sequence.AddZeroInitializationStep(Entity.getType()); > + return; > + } > + > // - otherwise, no initialization is performed. > > // If a program calls for the default initialization of an object of > > Modified: cfe/trunk/test/Analysis/nullptr.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Analysis/nullptr.cpp?rev=349201&r1=349200&r2=349201&view=diff > > ============================================================================== > --- cfe/trunk/test/Analysis/nullptr.cpp (original) > +++ cfe/trunk/test/Analysis/nullptr.cpp Fri Dec 14 14:22:29 2018 > @@ -125,21 +125,16 @@ struct Type { > }; > > void shouldNotCrash() { > - decltype(nullptr) p; // expected-note{{'p' declared without an initial > value}} > - if (getSymbol()) // expected-note {{Assuming the condition is false}} > - // expected-note@-1{{Taking false branch}} > - // expected-note@-2{{Assuming the condition is false}} > - // expected-note@-3{{Taking false branch}} > - // expected-note@-4{{Assuming the condition is true}} > - // expected-note@-5{{Taking true branch}} > - invokeF(p); // expected-warning{{1st function call argument is an > uninitialized value}} > - // expected-note@-1{{1st function call argument is an > uninitialized value}} > + decltype(nullptr) p; // expected-note{{'p' initialized to a null > pointer value}} > if (getSymbol()) // expected-note {{Assuming the condition is false}} > // expected-note@-1{{Taking false branch}} > // expected-note@-2{{Assuming the condition is true}} > // expected-note@-3{{Taking true branch}} > - invokeF(nullptr); // expected-note {{Calling 'invokeF'}} > - // expected-note@-1{{Passing null pointer value > via 1st parameter 'x'}} > + invokeF(p); // expected-note{{Passing null pointer value via 1st > parameter 'x'}} > + // expected-note@-1{{Calling 'invokeF'}} > + if (getSymbol()) // expected-note {{Assuming the condition is false}} > + // expected-note@-1{{Taking false branch}} > + invokeF(nullptr); > if (getSymbol()) { // expected-note {{Assuming the condition is true}} > // expected-note@-1{{Taking true branch}} > X *xx = Type().x; // expected-note {{Null pointer value stored to > field 'x'}} > > Modified: cfe/trunk/test/SemaCXX/ast-print-crash.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/ast-print-crash.cpp?rev=349201&r1=349200&r2=349201&view=diff > > ============================================================================== > --- cfe/trunk/test/SemaCXX/ast-print-crash.cpp (original) > +++ cfe/trunk/test/SemaCXX/ast-print-crash.cpp Fri Dec 14 14:22:29 2018 > @@ -7,6 +7,6 @@ > > // CHECK: struct { > // CHECK-NEXT: } dont_crash_on_syntax_error; > -// CHECK-NEXT: decltype(nullptr) p; > +// CHECK-NEXT: decltype(nullptr) p(/*implicit*/(decltype(nullptr))0); > struct { > } dont_crash_on_syntax_error /* missing ; */ decltype(nullptr) p; > > Added: cfe/trunk/test/SemaCXX/nullptr_t-init.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/nullptr_t-init.cpp?rev=349201&view=auto > > ============================================================================== > --- cfe/trunk/test/SemaCXX/nullptr_t-init.cpp (added) > +++ cfe/trunk/test/SemaCXX/nullptr_t-init.cpp Fri Dec 14 14:22:29 2018 > @@ -0,0 +1,10 @@ > +// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 -ffreestanding > -Wuninitialized %s > +// expected-no-diagnostics > +typedef decltype(nullptr) nullptr_t; > + > +// Ensure no 'uninitialized when used here' warnings (Wuninitialized), > for > +// nullptr_t always-initialized extension. > +nullptr_t default_init() { > + nullptr_t a; > + return a; > +} > > Propchange: cfe/trunk/test/SemaCXX/nullptr_t-init.cpp > > ------------------------------------------------------------------------------ > svn:eol-style = native > > Propchange: cfe/trunk/test/SemaCXX/nullptr_t-init.cpp > > ------------------------------------------------------------------------------ > svn:keywords = "Author Date Id Rev URL" > > Propchange: cfe/trunk/test/SemaCXX/nullptr_t-init.cpp > > ------------------------------------------------------------------------------ > svn:mime-type = text/plain > > > _______________________________________________ > cfe-commits mailing list > cfe-commits@lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits > > _______________________________________________ > cfe-commits mailing list > cfe-commits@lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >
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