[Clang] CWG2749: relational operators involving pointers to void #93046
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@llvm/pr-subscribers-clang Author: Mital Ashok (MitalAshok) ChangesThis DR's effects are backported to C++98. Does not affect C where integral constant expressions cannot involve pointers. Full diff: https://github.com/llvm/llvm-project/pull/93046.diff 7 Files Affected:
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 2899bc5ed35ad..4d9313f4c7ca5 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 a024f9b2a9f8c..b7aae9395e635 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 f1aa19e4409e1..d5a47a071e2cd 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 c160be06dd241..ae7942aca39e6 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 53ddd566b7dbf..f0c3c6dbdf97b 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@-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@-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@-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 e3cd057baba75..16e9329cccd4b 100644
--- a/clang/test/CXX/expr/expr.const/p2-0x.cpp
+++ b/clang/test/CXX/expr/expr.const/p2-0x.cpp
@@ -579,10 +579,10 @@ namespace UnspecifiedRelations {
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 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 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 9d458330f5376..26f2f60025e8e 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>
|
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.
MitalAshok
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Endilll
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May 30, 2024
Endilll
reviewed
May 30, 2024
Co-authored-by: Vlad Serebrennikov <[email protected]>
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@MitalAshok can you fix the conflicts and ping me so i can merge? |
|
@cor3ntin Done! |
|
@MitalAshok there is a test failure! |
|
LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/123/builds/4974 Here is the relevant piece of the build log for the reference |
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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.
Closes #45653