<limits>: fix traps for integers

stl/inc/limits

@@ -120,7 +120,10 @@ struct _Num_int_base : _Num_base { // base for integer types
     static constexpr bool is_exact       = true;
     static constexpr bool is_integer     = true;
     static constexpr bool is_specialized = true;
-    static constexpr int radix           = 2;
+#if !defined(__clang__) || defined(_M_X64) && !defined(_M_ARM64EC) || defined(_M_IX86)
+    static constexpr bool traps = true;
+#endif
+    static constexpr int radix = 2;
 };
 
 struct _Num_float_base : _Num_base { // base for floating-point types
@@ -178,6 +181,7 @@ public:
         return 0;
     }
 
+    static constexpr bool traps = false;
     static constexpr int digits = 1;
 };
 
@@ -222,6 +226,7 @@ public:
 
     static constexpr bool is_signed = CHAR_MIN != 0;
     static constexpr bool is_modulo = CHAR_MIN == 0;
+    static constexpr bool traps     = false;
     static constexpr int digits     = 8 - (CHAR_MIN != 0);
     static constexpr int digits10   = 2;
 };
@@ -266,6 +271,7 @@ public:
     }
 
     static constexpr bool is_signed = true;
+    static constexpr bool traps     = false;
     static constexpr int digits     = 7;
     static constexpr int digits10   = 2;
 };
@@ -310,6 +316,7 @@ public:
     }
 
     static constexpr bool is_modulo = true;
+    static constexpr bool traps     = false;
     static constexpr int digits     = 8;
     static constexpr int digits10   = 2;
 };
@@ -355,6 +362,7 @@ public:
     }
 
     static constexpr bool is_modulo = true;
+    static constexpr bool traps     = false;
     static constexpr int digits     = 8;
     static constexpr int digits10   = 2;
 };
@@ -400,6 +408,7 @@ public:
     }
 
     static constexpr bool is_modulo = true;
+    static constexpr bool traps     = false;
     static constexpr int digits     = 16;
     static constexpr int digits10   = 4;
 };
@@ -488,6 +497,7 @@ public:
     }
 
     static constexpr bool is_modulo = true;
+    static constexpr bool traps     = false;
     static constexpr int digits     = 16;
     static constexpr int digits10   = 4;
 };
@@ -532,6 +542,7 @@ public:
     }
 
     static constexpr bool is_signed = true;
+    static constexpr bool traps     = false;
     static constexpr int digits     = 15;
     static constexpr int digits10   = 4;
 };
@@ -710,6 +721,7 @@ public:
     }
 
     static constexpr bool is_modulo = true;
+    static constexpr bool traps     = false;
     static constexpr int digits     = 16;
     static constexpr int digits10   = 4;
 };

tests/libcxx/expected_results.txt

@@ -733,11 +733,6 @@ std/depr/depr.c.headers/tgmath_h.pass.cpp:2 FAIL
 
 
 # *** CLANG ISSUES, NOT YET ANALYZED ***
-# Not analyzed. Clang apparently defines platform macros differently from C1XX.
-# The test inspects `__x86_64__` and `__i386__`, which MSVC doesn't define.
-# SKIPPED because this fails for x64/x86 and passes for ARM64.
-std/language.support/support.limits/limits/numeric.limits.members/traps.pass.cpp:2 SKIPPED
-
 # Not analyzed. Possibly C++20 equality operator rewrite issues.
 std/utilities/expected/expected.expected/equality/equality.other_expected.pass.cpp:2 FAIL
 std/utilities/expected/expected.void/equality/equality.other_expected.pass.cpp:2 FAIL
@@ -996,6 +991,15 @@ std/containers/sequences/vector/trivial_relocation.pass.cpp:1 FAIL
 # Not analyzed, likely bogus test. constexpr fails with "vector iterators incompatible".
 std/ranges/range.adaptors/range.join.with/range.join.with.iterator/ctor.default.pass.cpp FAIL
 
+# Problems in this test:
+# - Clang does not trap on Arm64, but MSVC does.
+# - The test inspects `__x86_64__` and `__i386__`, which MSVC doesn't define.
+# - The __x86_64__ is defined on ARM64EC, but it is expected to behave like ARM64
+# :2 SKIPPED because this passes for x64/x86/ARM64 and fails for ARM64EC.
+std/language.support/support.limits/limits/numeric.limits.members/traps.pass.cpp:0 FAIL
+std/language.support/support.limits/limits/numeric.limits.members/traps.pass.cpp:1 FAIL
+std/language.support/support.limits/limits/numeric.limits.members/traps.pass.cpp:2 SKIPPED
+
 
 # *** LIKELY STL BUGS ***
 # Not analyzed, likely STL bugs. Various assertions.

tests/std/test.lst

@@ -272,6 +272,7 @@ tests\GH_005546_containers_size_type_cast
 tests\GH_005553_regex_character_translation
 tests\GH_005768_pow_accuracy
 tests\GH_005800_stable_sort_large_alignment
+tests\GH_005816_numeric_limits_traps
 tests\LWG2381_num_get_floating_point
 tests\LWG2510_tag_classes
 tests\LWG2597_complex_branch_cut

tests/std/tests/GH_005816_numeric_limits_traps/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\usual_matrix.lst

tests/std/tests/GH_005816_numeric_limits_traps/test.compile.pass.cpp

@@ -0,0 +1,40 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <limits>
+
+template <class T>
+constexpr bool traps_ = std::numeric_limits<T>::traps;
+
+#if defined(_M_IX86) || defined(_M_X64) && !defined(_M_ARM64EC)
+static_assert(traps_<int>,
+    "The #ED hardware exception always happens for zero division and for division overflow INT_MIN/-1. "
+    "It is translated to the corresponding SEH exceptions");
+#elif defined(_M_ARM64) || defined(_M_ARM64EC) || defined(_M_HYBRID_X86_ARM64)
+#ifdef __clang__
+static_assert(!traps_<int>, "The hardware does not trap. Clang compiles code as is, so there's no trap");
+#else // ^^^ defined(__clang__) / !defined(__clang__) vvv
+static_assert(traps_<int>, "The hardware does not trap. MSVC inserts check for zero to trap zero division. "
+                           "It does not insert checks for INT_MIN/-1 division overflow though");
+#endif // ^^^ !defined(__clang__) ^^^
+#else // ^^^ defined(_M_ARM64) || defined(_M_ARM64EC) || defined(_M_HYBRID_X86_ARM64) ^^^
+#error Unsupported hardware
+#endif
+
+static_assert(traps_<unsigned int> == traps_<int> && traps_<char32_t> == traps_<int> //
+                  && traps_<long> == traps_<int> && traps_<unsigned long> == traps_<int>
+                  && traps_<long long> == traps_<int> && traps_<unsigned long long> == traps_<int>,
+    "all non-promoted integers should trap or not trap equally");
+
+static_assert(!traps_<bool>, "bool does not trap for a moot reason; see LWG-554 resolution");
+
+static_assert(!traps_<char> && !traps_<signed char> && !traps_<unsigned char> //
+                  && !traps_<short> && !traps_<unsigned short> && !traps_<wchar_t> && !traps_<char16_t>,
+    "promoted integers do not trap for a moot reason; see LWG-554 resolution");
+
+#ifdef __cpp_char8_t
+static_assert(!traps_<char8_t>, "promoted integers do not trap for a moot reason; see LWG-554 resolution");
+#endif
+
+static_assert(!traps_<float> && !traps_<double> && !traps_<long double>,
+    "floats don't trap because even if '/fp:except' is passed, it should be enabled at runtime");