[clang] [Headers][X86] Allow AVX512fp16 initialization intrinsics to be used in constexpr (PR #159929)

[Shreeyash Pandey via cfe-commits]

https://github.com/bojle created https://github.com/llvm/llvm-project/pull/159929

Fixes https://github.com/llvm/llvm-project/issues/156866

>From 6eb518498bbc03232385b99f422324c09965b183 Mon Sep 17 00:00:00 2001
From: Shreeyash Pandey <shreeyash335 at gmail.com>
Date: Fri, 12 Sep 2025 19:59:34 +0530
Subject: [PATCH 1/2] [AVX-512] make AVX512fp16 constexpr and add tests

Signed-off-by: Shreeyash Pandey <shreeyash335 at gmail.com>
---
 clang/lib/Headers/avx512vlfp16intrin.h         | 4 ++--
 clang/test/CodeGen/X86/avx512vlfp16-builtins.c | 1 +
 clang/test/CodeGen/X86/builtin_test_helpers.h  | 1 +
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Headers/avx512vlfp16intrin.h b/clang/lib/Headers/avx512vlfp16intrin.h
index 8eb31eae6173b..0b68637bdd507 100644
--- a/clang/lib/Headers/avx512vlfp16intrin.h
+++ b/clang/lib/Headers/avx512vlfp16intrin.h
@@ -42,7 +42,7 @@ static __inline__ _Float16 __DEFAULT_FN_ATTRS256 _mm256_cvtsh_h(__m256h __a) {
   return __a[0];
 }
 
-static __inline__ __m128h __DEFAULT_FN_ATTRS128 _mm_set_sh(_Float16 __h) {
+static __inline__ __m128h __DEFAULT_FN_ATTRS128_CONSTEXPR _mm_set_sh(_Float16 __h) {
   return __extension__(__m128h){__h, 0, 0, 0, 0, 0, 0, 0};
 }
 
@@ -57,7 +57,7 @@ _mm256_set1_ph(_Float16 __h) {
                             __h, __h, __h, __h, __h, __h, __h, __h};
 }
 
-static __inline __m128h __DEFAULT_FN_ATTRS128
+static __inline __m128h __DEFAULT_FN_ATTRS128_CONSTEXPR
 _mm_set_ph(_Float16 __h1, _Float16 __h2, _Float16 __h3, _Float16 __h4,
            _Float16 __h5, _Float16 __h6, _Float16 __h7, _Float16 __h8) {
   return (__m128h)(__v8hf){__h8, __h7, __h6, __h5, __h4, __h3, __h2, __h1};
diff --git a/clang/test/CodeGen/X86/avx512vlfp16-builtins.c b/clang/test/CodeGen/X86/avx512vlfp16-builtins.c
index fd6ea8fe6056d..14125886ff814 100644
--- a/clang/test/CodeGen/X86/avx512vlfp16-builtins.c
+++ b/clang/test/CodeGen/X86/avx512vlfp16-builtins.c
@@ -110,6 +110,7 @@ __m128h test_mm_set_ph(_Float16 __h1, _Float16 __h2, _Float16 __h3, _Float16 __h
   // CHECK: insertelement <8 x half> {{.*}}, i32 7
   return _mm_set_ph(__h1, __h2, __h3, __h4, __h5, __h6, __h7, __h8);
 }
+TEST_CONSTEXPR(match_m128h(_mm_set_ph(1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0), 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.0, 1.0));
 
 __m256h test_mm256_set_ph(_Float16 __h1, _Float16 __h2, _Float16 __h3, _Float16 __h4,
                           _Float16 __h5, _Float16 __h6, _Float16 __h7, _Float16 __h8,
diff --git a/clang/test/CodeGen/X86/builtin_test_helpers.h b/clang/test/CodeGen/X86/builtin_test_helpers.h
index fcaf360626a2d..44c2dc7ba808b 100644
--- a/clang/test/CodeGen/X86/builtin_test_helpers.h
+++ b/clang/test/CodeGen/X86/builtin_test_helpers.h
@@ -4,6 +4,7 @@
 
 #if defined(__cplusplus) && (__cplusplus >= 201103L)
 
+
 constexpr bool match_m64(__m64 _v, unsigned long long a) {
   __v1du v = (__v1du)_v;
   return v[0] == a;

>From b52baea59848c054e400cb40860642581019ee62 Mon Sep 17 00:00:00 2001
From: Shreeyash Pandey <shreeyash335 at gmail.com>
Date: Fri, 12 Sep 2025 20:13:25 +0530
Subject: [PATCH 2/2] [AVX-512] add set_ph

Signed-off-by: Shreeyash Pandey <shreeyash335 at gmail.com>
---
 clang/test/CodeGen/X86/avx512vlfp16-builtins.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/clang/test/CodeGen/X86/avx512vlfp16-builtins.c b/clang/test/CodeGen/X86/avx512vlfp16-builtins.c
index 14125886ff814..0ed176984bcdc 100644
--- a/clang/test/CodeGen/X86/avx512vlfp16-builtins.c
+++ b/clang/test/CodeGen/X86/avx512vlfp16-builtins.c
@@ -37,6 +37,8 @@ __m128h test_mm_set_sh(_Float16 __h) {
   return _mm_set_sh(__h);
 }
 
+TEST_CONSTEXPR(match_m128h(_mm_set_sh(2.0), 2.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0));
+
 __m128h test_mm_set1_ph(_Float16 h) {
   // CHECK-LABEL: test_mm_set1_ph
   // CHECK: insertelement <8 x half> {{.*}}, i32 0