[libcxx-commits] [libcxx] [libcxx][test] Stop testing signaling NaN in the constexpr comparison functions (PR #222542)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Cyrus Ding (dingcyrus)

<details>
<summary>Changes</summary>

std::isgreater, std::isgreaterequal, std::islessequal and std::isunordered behave like the corresponding C macros, which may raise the "invalid" floating-point exception when an operand is a signaling NaN ([c.math.fpclass]/1, C23 7.12.17). Raising a floating-point exception is not allowed during constant evaluation, so passing signaling_NaN() to these functions in a constexpr context is bogus; MSVC's implementation rejects it.

Remove the signaling NaN asserts from the four affected tests. The classification functions (isnan, isinf, fpclassify, ...) are affected: the standard guarantees they never raise for signaling NaN, so their existing sNaN tests remain valid.

Fixes #<!-- -->222431

---
Full diff: https://github.com/llvm/llvm-project/pull/222542.diff


4 Files Affected:

- (modified) libcxx/test/std/numerics/c.math/isgreater.pass.cpp (+2-1) 
- (modified) libcxx/test/std/numerics/c.math/isgreaterequal.pass.cpp (+2-1) 
- (modified) libcxx/test/std/numerics/c.math/islessequal.pass.cpp (+2-1) 
- (modified) libcxx/test/std/numerics/c.math/isunordered.pass.cpp (+2-1) 


``````````diff
diff --git a/libcxx/test/std/numerics/c.math/isgreater.pass.cpp b/libcxx/test/std/numerics/c.math/isgreater.pass.cpp
index e09680edf50e1..31ba3d03dd87f 100644
--- a/libcxx/test/std/numerics/c.math/isgreater.pass.cpp
+++ b/libcxx/test/std/numerics/c.math/isgreater.pass.cpp
@@ -32,7 +32,8 @@ struct TestFloat {
     assert(!std::isgreater(lim::quiet_NaN(), T(0)));
     assert(!std::isgreater(T(0), lim::quiet_NaN()));
     assert(!std::isgreater(lim::quiet_NaN(), lim::quiet_NaN()));
-    assert(!std::isgreater(lim::signaling_NaN(), T(0)));
+    // Note: signaling NaN is intentionally not tested. Passing a signaling NaN to these macros may
+    // raise the "invalid" floating-point exception, which is not allowed during constant evaluation.
   }
 };
 
diff --git a/libcxx/test/std/numerics/c.math/isgreaterequal.pass.cpp b/libcxx/test/std/numerics/c.math/isgreaterequal.pass.cpp
index a1f03253247ca..f28e6139c3991 100644
--- a/libcxx/test/std/numerics/c.math/isgreaterequal.pass.cpp
+++ b/libcxx/test/std/numerics/c.math/isgreaterequal.pass.cpp
@@ -31,7 +31,8 @@ struct TestFloat {
 
     assert(!std::isgreaterequal(lim::quiet_NaN(), T(0)));
     assert(!std::isgreaterequal(T(0), lim::quiet_NaN()));
-    assert(!std::isgreaterequal(lim::signaling_NaN(), T(0)));
+    // Note: signaling NaN is intentionally not tested. Passing a signaling NaN to these macros may
+    // raise the "invalid" floating-point exception, which is not allowed during constant evaluation.
   }
 };
 
diff --git a/libcxx/test/std/numerics/c.math/islessequal.pass.cpp b/libcxx/test/std/numerics/c.math/islessequal.pass.cpp
index 34b5cacd584e5..1fd590217788f 100644
--- a/libcxx/test/std/numerics/c.math/islessequal.pass.cpp
+++ b/libcxx/test/std/numerics/c.math/islessequal.pass.cpp
@@ -31,7 +31,8 @@ struct TestFloat {
 
     assert(!std::islessequal(lim::quiet_NaN(), T(0)));
     assert(!std::islessequal(T(0), lim::quiet_NaN()));
-    assert(!std::islessequal(lim::signaling_NaN(), T(0)));
+    // Note: signaling NaN is intentionally not tested. Passing a signaling NaN to these macros may
+    // raise the "invalid" floating-point exception, which is not allowed during constant evaluation.
   }
 };
 
diff --git a/libcxx/test/std/numerics/c.math/isunordered.pass.cpp b/libcxx/test/std/numerics/c.math/isunordered.pass.cpp
index bb13d46768a69..79cc56c50a5ca 100644
--- a/libcxx/test/std/numerics/c.math/isunordered.pass.cpp
+++ b/libcxx/test/std/numerics/c.math/isunordered.pass.cpp
@@ -27,8 +27,9 @@ struct TestFloat {
     assert(std::isunordered(lim::quiet_NaN(), T(0)));
     assert(std::isunordered(T(0), lim::quiet_NaN()));
     assert(std::isunordered(lim::quiet_NaN(), lim::quiet_NaN()));
+    // Note: signaling NaN is intentionally not tested. Passing a signaling NaN to these macros may
+    // raise the "invalid" floating-point exception, which is not allowed during constant evaluation.
 
-    assert(std::isunordered(lim::signaling_NaN(), T(0)));
     assert(!std::isunordered(lim::infinity(), lim::infinity()));
     assert(!std::isunordered(lim::max(), lim::lowest()));
   }

``````````

</details>


https://github.com/llvm/llvm-project/pull/222542