r349201 - Add extension to always default-initialize nullptr_t.
Richard Smith via cfe-commits
cfe-commits at lists.llvm.org
Fri Dec 14 14:40:41 PST 2018
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 at 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 at -1{{Taking false branch}}
> - // expected-note at -2{{Assuming the condition is false}}
> - // expected-note at -3{{Taking false branch}}
> - // expected-note at -4{{Assuming the condition is true}}
> - // expected-note at -5{{Taking true branch}}
> - invokeF(p); // expected-warning{{1st function call argument is an
> uninitialized value}}
> - // expected-note at -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 at -1{{Taking false branch}}
> // expected-note at -2{{Assuming the condition is true}}
> // expected-note at -3{{Taking true branch}}
> - invokeF(nullptr); // expected-note {{Calling 'invokeF'}}
> - // expected-note at -1{{Passing null pointer value
> via 1st parameter 'x'}}
> + invokeF(p); // expected-note{{Passing null pointer value via 1st
> parameter 'x'}}
> + // expected-note at -1{{Calling 'invokeF'}}
> + if (getSymbol()) // expected-note {{Assuming the condition is false}}
> + // expected-note at -1{{Taking false branch}}
> + invokeF(nullptr);
> if (getSymbol()) { // expected-note {{Assuming the condition is true}}
> // expected-note at -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
>
>
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