[Headers][X86] Allow _mm512_set1_epi8/16/pd/ps intrinsics to be used in constexpr (#152746)

Pulled out of #152288 as I need this to proceed with several other patches

Author: RKSimon

clang/lib/Headers/avx512fintrin.h

@@ -277,20 +277,20 @@ _mm512_setzero_pd(void) {
   return __extension__(__m512d){0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0};
 }
 
-static __inline __m512 __DEFAULT_FN_ATTRS512
+static __inline __m512 __DEFAULT_FN_ATTRS512_CONSTEXPR
 _mm512_set1_ps(float __w)
 {
   return __extension__ (__m512){ __w, __w, __w, __w, __w, __w, __w, __w,
                                  __w, __w, __w, __w, __w, __w, __w, __w  };
 }
 
-static __inline __m512d __DEFAULT_FN_ATTRS512
+static __inline __m512d __DEFAULT_FN_ATTRS512_CONSTEXPR
 _mm512_set1_pd(double __w)
 {
   return __extension__ (__m512d){ __w, __w, __w, __w, __w, __w, __w, __w };
 }
 
-static __inline __m512i __DEFAULT_FN_ATTRS512
+static __inline __m512i __DEFAULT_FN_ATTRS512_CONSTEXPR
 _mm512_set1_epi8(char __w)
 {
   return __extension__ (__m512i)(__v64qi){
@@ -304,7 +304,7 @@ _mm512_set1_epi8(char __w)
     __w, __w, __w, __w, __w, __w, __w, __w  };
 }
 
-static __inline __m512i __DEFAULT_FN_ATTRS512
+static __inline __m512i __DEFAULT_FN_ATTRS512_CONSTEXPR
 _mm512_set1_epi16(short __w)
 {
   return __extension__ (__m512i)(__v32hi){

clang/test/CodeGen/X86/avx512f-builtins.c

@@ -439,6 +439,22 @@ __m512d test_mm512_set1_pd(double d)
   // CHECK: insertelement <8 x double> {{.*}}, i32 7
   return _mm512_set1_pd(d);
 }
+TEST_CONSTEXPR(match_m512d(_mm512_set1_pd(-100.0), -100.0, -100.0, -100.0, -100.0, -100.0, -100.0, -100.0, -100.0));
+
+__m512 test_mm512_set1_ps(float d)
+{
+  // CHECK-LABEL: test_mm512_set1_ps
+  // CHECK: insertelement <16 x float> {{.*}}, i32 0
+  // CHECK: insertelement <16 x float> {{.*}}, i32 1
+  // CHECK: insertelement <16 x float> {{.*}}, i32 2
+  // CHECK: insertelement <16 x float> {{.*}}, i32 3
+  // CHECK: insertelement <16 x float> {{.*}}, i32 4
+  // CHECK: insertelement <16 x float> {{.*}}, i32 5
+  // CHECK: insertelement <16 x float> {{.*}}, i32 6
+  // CHECK: insertelement <16 x float> {{.*}}, i32 15
+  return _mm512_set1_ps(d);
+}
+TEST_CONSTEXPR(match_m512(_mm512_set1_ps(-55.0f), -55.0f, -55.0f, -55.0f, -55.0f, -55.0f, -55.0f, -55.0f, -55.0f, -55.0f, -55.0f, -55.0f, -55.0f, -55.0f, -55.0f, -55.0f, -55.0f));
 
 __mmask16 test_mm512_knot(__mmask16 a)
 {
@@ -9046,6 +9062,7 @@ __m512i test_mm512_set1_epi8(char d)
   // CHECK: insertelement <64 x i8> {{.*}}, i32 63
   return _mm512_set1_epi8(d);
 }
+TEST_CONSTEXPR(match_v64qi(_mm512_set1_epi8(127), 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127, 127));
 
 __m512i test_mm512_set1_epi16(short d)
 {
@@ -9061,6 +9078,7 @@ __m512i test_mm512_set1_epi16(short d)
   // CHECK: insertelement <32 x i16> {{.*}}, i32 31
   return _mm512_set1_epi16(d);
 }
+TEST_CONSTEXPR(match_v32hi(_mm512_set1_epi16(-511), -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511, -511));
 
 __m512i test_mm512_set1_epi32(int d)
 {