[clang] [Clang] CWG2749: relational operators involving pointers to void (PR #93046)
Mital Ashok via cfe-commits
cfe-commits at lists.llvm.org
Thu Sep 5 04:19:37 PDT 2024
https://github.com/MitalAshok updated https://github.com/llvm/llvm-project/pull/93046
>From e1172958f43af7490b5b6e3752a9070265ad17ca Mon Sep 17 00:00:00 2001
From: Mital Ashok <mital at mitalashok.co.uk>
Date: Wed, 22 May 2024 16:01:13 +0100
Subject: [PATCH 1/5] [Clang] CWG2749: relational operators involving pointers
to void
https://cplusplus.github.io/CWG/issues/2749.html
This DR's effects are backported to C++98.
Does not affect C where integral constant expressions cannot involve pointers.
---
clang/docs/ReleaseNotes.rst | 4 ++
.../include/clang/Basic/DiagnosticASTKinds.td | 2 -
clang/lib/AST/ExprConstant.cpp | 10 ----
clang/test/AST/Interp/literals.cpp | 8 +---
clang/test/CXX/drs/cwg27xx.cpp | 46 ++++++++++++++++++-
clang/test/CXX/expr/expr.const/p2-0x.cpp | 11 +++--
clang/www/cxx_dr_status.html | 2 +-
7 files changed, 58 insertions(+), 25 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 2899bc5ed35ad0..4d9313f4c7ca57 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -237,6 +237,10 @@ Resolutions to C++ Defect Reports
- P0522 implementation is enabled by default in all language versions, and
provisional wording for CWG2398 is implemented.
+- Clang now allows comparing unequal object pointers that have been cast to ``void *``
+ in constant expressions. These comparisons always worked in non-constant expressions.
+ (`CWG2749: Treatment of "pointer to void" for relational comparisons <https://cplusplus.github.io/CWG/issues/2749.html>`_).
+
C Language Changes
------------------
diff --git a/clang/include/clang/Basic/DiagnosticASTKinds.td b/clang/include/clang/Basic/DiagnosticASTKinds.td
index a024f9b2a9f8c0..b7aae9395e6357 100644
--- a/clang/include/clang/Basic/DiagnosticASTKinds.td
+++ b/clang/include/clang/Basic/DiagnosticASTKinds.td
@@ -148,8 +148,6 @@ def note_constexpr_var_init_weak : Note<
def note_constexpr_typeid_polymorphic : Note<
"typeid applied to expression of polymorphic type %0 is "
"not allowed in a constant expression in C++ standards before C++20">;
-def note_constexpr_void_comparison : Note<
- "comparison between unequal pointers to void has unspecified result">;
def note_constexpr_temporary_here : Note<"temporary created here">;
def note_constexpr_dynamic_alloc_here : Note<"heap allocation performed here">;
def note_constexpr_conditional_never_const : Note<
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index f1aa19e4409e15..d5a47a071e2cd7 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -13627,16 +13627,6 @@ EvaluateComparisonBinaryOperator(EvalInfo &Info, const BinaryOperator *E,
SubobjectDesignator &LHSDesignator = LHSValue.getLValueDesignator();
SubobjectDesignator &RHSDesignator = RHSValue.getLValueDesignator();
- // C++11 [expr.rel]p3:
- // Pointers to void (after pointer conversions) can be compared, with a
- // result defined as follows: If both pointers represent the same
- // address or are both the null pointer value, the result is true if the
- // operator is <= or >= and false otherwise; otherwise the result is
- // unspecified.
- // We interpret this as applying to pointers to *cv* void.
- if (LHSTy->isVoidPointerType() && LHSOffset != RHSOffset && IsRelational)
- Info.CCEDiag(E, diag::note_constexpr_void_comparison);
-
// C++11 [expr.rel]p2:
// - If two pointers point to non-static data members of the same object,
// or to subobjects or array elements fo such members, recursively, the
diff --git a/clang/test/AST/Interp/literals.cpp b/clang/test/AST/Interp/literals.cpp
index c160be06dd241c..ae7942aca39e63 100644
--- a/clang/test/AST/Interp/literals.cpp
+++ b/clang/test/AST/Interp/literals.cpp
@@ -191,12 +191,8 @@ namespace PointerComparison {
constexpr bool v3 = null == pv; // ok
constexpr bool v4 = qv == pv; // ok
- /// FIXME: These two are rejected by the current interpreter, but
- /// accepted by GCC.
- constexpr bool v5 = qv >= pv; // ref-error {{constant expression}} \
- // ref-note {{unequal pointers to void}}
- constexpr bool v8 = qv > (void*)&s.a; // ref-error {{constant expression}} \
- // ref-note {{unequal pointers to void}}
+ constexpr bool v5 = qv >= pv;
+ constexpr bool v8 = qv > (void*)&s.a;
constexpr bool v6 = qv > null; // both-error {{must be initialized by a constant expression}} \
// both-note {{comparison between '&s.b' and 'nullptr' has unspecified value}}
diff --git a/clang/test/CXX/drs/cwg27xx.cpp b/clang/test/CXX/drs/cwg27xx.cpp
index 53ddd566b7dbf9..f0c3c6dbdf97b0 100644
--- a/clang/test/CXX/drs/cwg27xx.cpp
+++ b/clang/test/CXX/drs/cwg27xx.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++98 -verify=expected %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++98 -Wgnu-folding-constant -verify=expected %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++11 -verify=expected %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++14 -verify=expected %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++17 -verify=expected %s
@@ -6,6 +6,18 @@
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++23 -verify=expected,since-cxx23 %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++2c -verify=expected,since-cxx23,since-cxx26 %s
+namespace std {
+#if __cplusplus >= 202002L
+ struct strong_ordering {
+ int n;
+ constexpr operator int() const { return n; }
+ static const strong_ordering less, equal, greater;
+ };
+ constexpr strong_ordering strong_ordering::less{-1},
+ strong_ordering::equal{0}, strong_ordering::greater{1};
+#endif
+}
+
namespace cwg2718 { // cwg2718: 2.7
struct B {};
struct D;
@@ -18,6 +30,38 @@ void f(B b) {
struct D : B {};
} // namespace cwg2718
+namespace cwg2749 { // cwg2749: 19
+
+extern int x[2];
+struct Y {
+ int i;
+ int j;
+};
+extern Y y[2];
+
+#if __cplusplus >= 201103L
+static_assert(static_cast<void*>(x + 0) < static_cast<void*>(x + 1), "");
+static_assert(static_cast<void*>(&y[0].i) < static_cast<void*>(&y[0].j), "");
+static_assert(static_cast<void*>(&y[0].j) < static_cast<void*>(&y[1].i), "");
+#else
+enum X {
+ a = static_cast<void*>(x + 0) < static_cast<void*>(x + 1),
+// expected-warning at -1 {{expression is not an integral constant expression; folding it to a constant is a GNU extension}}
+ b = static_cast<void*>(&y[0].i) < static_cast<void*>(&y[0].j),
+// expected-warning at -1 {{expression is not an integral constant expression; folding it to a constant is a GNU extension}}
+ c = static_cast<void*>(&y[0].j) < static_cast<void*>(&y[1].i)
+// expected-warning at -1 {{expression is not an integral constant expression; folding it to a constant is a GNU extension}}
+};
+#endif
+
+#if __cplusplus >= 202002L
+static_assert((static_cast<void*>(x + 0) <=> static_cast<void*>(x + 1)) == std::strong_ordering::less);
+static_assert((static_cast<void*>(&y[0].i) <=> static_cast<void*>(&y[0].j)) == std::strong_ordering::less);
+static_assert((static_cast<void*>(&y[0].j) <=> static_cast<void*>(&y[1].i)) == std::strong_ordering::less);
+#endif
+
+} // namespace cwg2749
+
namespace cwg2759 { // cwg2759: 19
#if __cplusplus >= 201103L
diff --git a/clang/test/CXX/expr/expr.const/p2-0x.cpp b/clang/test/CXX/expr/expr.const/p2-0x.cpp
index e3cd057baba75f..767eee1c74f054 100644
--- a/clang/test/CXX/expr/expr.const/p2-0x.cpp
+++ b/clang/test/CXX/expr/expr.const/p2-0x.cpp
@@ -571,18 +571,19 @@ namespace UnspecifiedRelations {
// [expr.rel]p3: Pointers to void can be compared [...] if both pointers
// represent the same address or are both the null pointer [...]; otherwise
// the result is unspecified.
+ // Same address restriction removed by CWG2749
struct S { int a, b; } s;
constexpr void *null = 0;
constexpr void *pv = (void*)&s.a;
constexpr void *qv = (void*)&s.b;
constexpr bool v1 = null < (int*)0;
constexpr bool v2 = null < pv; // expected-error {{constant expression}} expected-note {{comparison between 'nullptr' and '&s.a' has unspecified value}}
- constexpr bool v3 = null == pv; // ok
- constexpr bool v4 = qv == pv; // ok
- constexpr bool v5 = qv >= pv; // expected-error {{constant expression}} expected-note {{unequal pointers to void}}
+ constexpr bool v3 = null == pv;
+ constexpr bool v4 = qv == pv;
+ constexpr bool v5 = qv >= pv;
constexpr bool v6 = qv > null; // expected-error {{constant expression}} expected-note {{comparison between '&s.b' and 'nullptr' has unspecified value}}
- constexpr bool v7 = qv <= (void*)&s.b; // ok
- constexpr bool v8 = qv > (void*)&s.a; // expected-error {{constant expression}} expected-note {{unequal pointers to void}}
+ constexpr bool v7 = qv <= (void*)&s.b;
+ constexpr bool v8 = qv > (void*)&s.a;
}
// - an assignment or a compound assignment (5.17); or
diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index 9d458330f53768..26f2f60025e8e7 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -16302,7 +16302,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
<td><a href="https://cplusplus.github.io/CWG/issues/2749.html">2749</a></td>
<td>DRWP</td>
<td>Treatment of "pointer to void" for relational comparisons</td>
- <td class="unknown" align="center">Unknown</td>
+ <td class="unreleased" align="center">Clang 19</td>
</tr>
<tr id="2750">
<td><a href="https://cplusplus.github.io/CWG/issues/2750.html">2750</a></td>
>From b54f2f90cf295c645d0d2256c0f611e161f960eb Mon Sep 17 00:00:00 2001
From: Mital Ashok <mital at mitalashok.co.uk>
Date: Thu, 30 May 2024 21:44:20 +0100
Subject: [PATCH 2/5] Constant fold in C++98 with __builtin_constant_p instead
of with enumerator
---
clang/test/CXX/drs/cwg27xx.cpp | 32 ++++++++++++++++----------------
1 file changed, 16 insertions(+), 16 deletions(-)
diff --git a/clang/test/CXX/drs/cwg27xx.cpp b/clang/test/CXX/drs/cwg27xx.cpp
index f0c3c6dbdf97b0..4c4581c0269ed7 100644
--- a/clang/test/CXX/drs/cwg27xx.cpp
+++ b/clang/test/CXX/drs/cwg27xx.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++98 -Wgnu-folding-constant -verify=expected %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++98 -verify=expected %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++11 -verify=expected %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++14 -verify=expected %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++17 -verify=expected %s
@@ -6,6 +6,17 @@
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++23 -verify=expected,since-cxx23 %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++2c -verify=expected,since-cxx23,since-cxx26 %s
+#if __cplusplus == 199711L
+#define static_assert(...) __extension__ _Static_assert(__VA_ARGS__)
+// cxx98-error at -1 {{variadic macros are a C99 feature}}
+#endif
+
+#if __cplusplus == 199711L
+#define __enable_constant_folding(x) (__builtin_constant_p(x) ? (x) : (x))
+#else
+#define __enable_constant_folding
+#endif
+
namespace std {
#if __cplusplus >= 202002L
struct strong_ordering {
@@ -39,23 +50,12 @@ struct Y {
};
extern Y y[2];
-#if __cplusplus >= 201103L
-static_assert(static_cast<void*>(x + 0) < static_cast<void*>(x + 1), "");
-static_assert(static_cast<void*>(&y[0].i) < static_cast<void*>(&y[0].j), "");
-static_assert(static_cast<void*>(&y[0].j) < static_cast<void*>(&y[1].i), "");
-#else
-enum X {
- a = static_cast<void*>(x + 0) < static_cast<void*>(x + 1),
-// expected-warning at -1 {{expression is not an integral constant expression; folding it to a constant is a GNU extension}}
- b = static_cast<void*>(&y[0].i) < static_cast<void*>(&y[0].j),
-// expected-warning at -1 {{expression is not an integral constant expression; folding it to a constant is a GNU extension}}
- c = static_cast<void*>(&y[0].j) < static_cast<void*>(&y[1].i)
-// expected-warning at -1 {{expression is not an integral constant expression; folding it to a constant is a GNU extension}}
-};
-#endif
+static_assert(__enable_constant_folding(static_cast<void*>(&x[0]) < static_cast<void*>(&x[1])), "");
+static_assert(__enable_constant_folding(static_cast<void*>(&y[0].i) < static_cast<void*>(&y[0].j)), "");
+static_assert(__enable_constant_folding(static_cast<void*>(&y[0].j) < static_cast<void*>(&y[1].i)), "");
#if __cplusplus >= 202002L
-static_assert((static_cast<void*>(x + 0) <=> static_cast<void*>(x + 1)) == std::strong_ordering::less);
+static_assert((static_cast<void*>(&x[0]) <=> static_cast<void*>(&x[1])) == std::strong_ordering::less);
static_assert((static_cast<void*>(&y[0].i) <=> static_cast<void*>(&y[0].j)) == std::strong_ordering::less);
static_assert((static_cast<void*>(&y[0].j) <=> static_cast<void*>(&y[1].i)) == std::strong_ordering::less);
#endif
>From 011463a95181bc09efd6bddb3d64361717aaddf3 Mon Sep 17 00:00:00 2001
From: Mital Ashok <mital.vaja at googlemail.com>
Date: Thu, 30 May 2024 22:41:13 +0100
Subject: [PATCH 3/5] Update clang/test/CXX/drs/cwg27xx.cpp
Co-authored-by: Vlad Serebrennikov <serebrennikov.vladislav at gmail.com>
---
clang/test/CXX/drs/cwg27xx.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/clang/test/CXX/drs/cwg27xx.cpp b/clang/test/CXX/drs/cwg27xx.cpp
index 4c4581c0269ed7..03ae800e1fb985 100644
--- a/clang/test/CXX/drs/cwg27xx.cpp
+++ b/clang/test/CXX/drs/cwg27xx.cpp
@@ -27,7 +27,7 @@ namespace std {
constexpr strong_ordering strong_ordering::less{-1},
strong_ordering::equal{0}, strong_ordering::greater{1};
#endif
-}
+} // namespace std
namespace cwg2718 { // cwg2718: 2.7
struct B {};
>From 2bedccfbbc587155a5b732d79d72ba9df7843981 Mon Sep 17 00:00:00 2001
From: Mital Ashok <mital at mitalashok.co.uk>
Date: Thu, 5 Sep 2024 09:21:19 +0100
Subject: [PATCH 4/5] Clang 19 -> 20
---
clang/test/CXX/drs/cwg27xx.cpp | 2 +-
clang/www/cxx_dr_status.html | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/clang/test/CXX/drs/cwg27xx.cpp b/clang/test/CXX/drs/cwg27xx.cpp
index a726f9f8d7a170..1c210cfc583f7d 100644
--- a/clang/test/CXX/drs/cwg27xx.cpp
+++ b/clang/test/CXX/drs/cwg27xx.cpp
@@ -41,7 +41,7 @@ void f(B b) {
struct D : B {};
} // namespace cwg2718
-namespace cwg2749 { // cwg2749: 19
+namespace cwg2749 { // cwg2749: 20
extern int x[2];
struct Y {
diff --git a/clang/www/cxx_dr_status.html b/clang/www/cxx_dr_status.html
index aec188bc1d6591..b638f0ff30bcce 100755
--- a/clang/www/cxx_dr_status.html
+++ b/clang/www/cxx_dr_status.html
@@ -16341,7 +16341,7 @@ <h2 id="cxxdr">C++ defect report implementation status</h2>
<td><a href="https://cplusplus.github.io/CWG/issues/2749.html">2749</a></td>
<td>DRWP</td>
<td>Treatment of "pointer to void" for relational comparisons</td>
- <td class="unreleased" align="center">Clang 19</td>
+ <td class="unreleased" align="center">Clang 20</td>
</tr>
<tr id="2750">
<td><a href="https://cplusplus.github.io/CWG/issues/2750.html">2750</a></td>
>From b1549ddc163084ab2f8950fa5c88bddeae7a7a55 Mon Sep 17 00:00:00 2001
From: Mital Ashok <mital at mitalashok.co.uk>
Date: Thu, 5 Sep 2024 12:19:21 +0100
Subject: [PATCH 5/5] Fix test failure
---
clang/test/CXX/drs/cwg27xx.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/clang/test/CXX/drs/cwg27xx.cpp b/clang/test/CXX/drs/cwg27xx.cpp
index 1c210cfc583f7d..b3867696c615b8 100644
--- a/clang/test/CXX/drs/cwg27xx.cpp
+++ b/clang/test/CXX/drs/cwg27xx.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++98 -pedantic-errors -verify=expected %s
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++98 -pedantic-errors -verify=expected,cxx98 %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++11 -pedantic-errors -verify=expected %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++14 -pedantic-errors -verify=expected %s
// RUN: %clang_cc1 -triple x86_64-linux-gnu -std=c++17 -pedantic-errors -verify=expected %s
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