r349201 - Add extension to always default-initialize nullptr_t.
Keane, Erich via cfe-commits
cfe-commits at lists.llvm.org
Fri Dec 14 14:42:30 PST 2018
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:richard at metafoo.co.uk]
Sent: Friday, December 14, 2018 2:41 PM
To: Keane, Erich <erich.keane at intel.com>
Cc: cfe-commits <cfe-commits at 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 at lists.llvm.org<mailto: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
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Propchange: cfe/trunk/test/SemaCXX/nullptr_t-init.cpp
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Propchange: cfe/trunk/test/SemaCXX/nullptr_t-init.cpp
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