[clang] [X86][Clang] Allow constexpr evaluation of F16C CVTPS2PH intrinsics (PR #162295)

[Hanyang Xu via cfe-commits]

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@@ -67,3 +67,60 @@ __m128i test_mm256_cvtps_ph(__m256 a) {
   // CHECK: call <8 x i16> @llvm.x86.vcvtps2ph.256(<8 x float> %{{.*}}, i32 0)
   return _mm256_cvtps_ph(a, 0);
 }
+
+// A value exactly halfway between 1.0 and the next representable FP16 number.
+// In binary, its significand ends in ...000, followed by a tie-bit 1.
+#define POS_HALFWAY (1.0f + 0.00048828125f) // 1.0 + 2^-11, a tie-breaking case
+
+//
+// __builtin_ia32_vcvtps2ph (128-bit, 4 floats -> 8 shorts, 4 are zero-padded)
+//
+// Test values: -2.5f, 1.123f, POS_HALFWAY
+TEST_CONSTEXPR(match_v8hi(
+  __builtin_ia32_vcvtps2ph(_mm_setr_ps(-2.5f, 1.123f, POS_HALFWAY, 0.0f), _MM_FROUND_TO_NEAREST_INT),
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ericxu233 wrote:

Done

https://github.com/llvm/llvm-project/pull/162295