[clang] [libcxx] [Clang] Allow __builtin_fma/fmaf/fmal to be used in a constant expression (PR #158048)

[Chaitanya Koparkar via cfe-commits]

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@@ -194,11 +194,19 @@ int main(int, char**) {
   ASSERT_NOT_CONSTEXPR_CXX23(std::fminf(1.0f, 0.0f) == 0.0f);
   ASSERT_NOT_CONSTEXPR_CXX23(std::fminl(1.0L, 0.0L) == 0.0L);
 
+#if !__has_constexpr_builtin(__builtin_fma)
   ASSERT_NOT_CONSTEXPR_CXX23(std::fma(1.0f, 1.0f, 1.0f) == 2.0f);
   ASSERT_NOT_CONSTEXPR_CXX23(std::fma(1.0, 1.0, 1.0) == 2.0);
   ASSERT_NOT_CONSTEXPR_CXX23(std::fma(1.0L, 1.0L, 1.0L) == 2.0L);
   ASSERT_NOT_CONSTEXPR_CXX23(std::fmaf(1.0f, 1.0f, 1.0f) == 2.0f);
   ASSERT_NOT_CONSTEXPR_CXX23(std::fmal(1.0L, 1.0L, 1.0L) == 2.0L);
+#else
+  ASSERT_CONSTEXPR_CXX23(std::fma(1.0f, 1.0f, 1.0f) == 2.0f);
+  ASSERT_CONSTEXPR_CXX23(std::fma(1.0, 1.0, 1.0) == 2.0);
+  ASSERT_CONSTEXPR_CXX23(std::fma(1.0L, 1.0L, 1.0L) == 2.0L);
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ckoparkar wrote:

Ah, yes. I was thinking whether I should also add `_LIBCPP_CONSTEXPR_SINCE_CXX23` to the corresponding functions in `fma.h`, but I'm now realizing that that's a separate thing altogether and shouldn't be done in this patch. Aright I'll just fix the tests here. Thanks!

https://github.com/llvm/llvm-project/pull/158048