[X86][AVX] Update _mm256_loadu2_m128* intrinsics to use _mm256_set_m128* (PR51796)

As reported on PR51796, the _mm256_loadu2_m128i in particular was inserting bitcasts and shuffles with different types making it trickier for some combines, and prevented the value tracker from identifying the shuffle sequences as a single insert_subvector style concat_vectors pattern.

This patch instead concatenate the 128-bit unaligned loads with _mm256_set_m128*, which was written to avoid the unnecessary bitcasts and only emits a single shuffle.

Differential Revision: https://reviews.llvm.org/D109497

Author: RKSimon

clang/lib/Headers/avxintrin.h

@@ -4902,8 +4902,7 @@ _mm256_setr_m128i (__m128i __lo, __m128i __hi)
 static __inline __m256 __DEFAULT_FN_ATTRS
 _mm256_loadu2_m128(float const *__addr_hi, float const *__addr_lo)
 {
-  __m256 __v256 = _mm256_castps128_ps256(_mm_loadu_ps(__addr_lo));
-  return _mm256_insertf128_ps(__v256, _mm_loadu_ps(__addr_hi), 1);
+  return _mm256_set_m128(_mm_loadu_ps(__addr_hi), _mm_loadu_ps(__addr_lo));
 }
 
 /// Loads two 128-bit floating-point vectors of [2 x double] from
@@ -4930,8 +4929,7 @@ _mm256_loadu2_m128(float const *__addr_hi, float const *__addr_lo)
 static __inline __m256d __DEFAULT_FN_ATTRS
 _mm256_loadu2_m128d(double const *__addr_hi, double const *__addr_lo)
 {
-  __m256d __v256 = _mm256_castpd128_pd256(_mm_loadu_pd(__addr_lo));
-  return _mm256_insertf128_pd(__v256, _mm_loadu_pd(__addr_hi), 1);
+  return _mm256_set_m128d(_mm_loadu_pd(__addr_hi), _mm_loadu_pd(__addr_lo));
 }
 
 /// Loads two 128-bit integer vectors from unaligned memory locations and
@@ -4955,8 +4953,7 @@ _mm256_loadu2_m128d(double const *__addr_hi, double const *__addr_lo)
 static __inline __m256i __DEFAULT_FN_ATTRS
 _mm256_loadu2_m128i(__m128i_u const *__addr_hi, __m128i_u const *__addr_lo)
 {
-  __m256i __v256 = _mm256_castsi128_si256(_mm_loadu_si128(__addr_lo));
-  return _mm256_insertf128_si256(__v256, _mm_loadu_si128(__addr_hi), 1);
+   return _mm256_set_m128i(_mm_loadu_si128(__addr_hi), _mm_loadu_si128(__addr_lo));
 }
 
 /* SIMD store ops (unaligned) */

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

@@ -1233,30 +1233,24 @@ __m256i test_mm256_loadu_si256(__m256i* A) {
 __m256 test_mm256_loadu2_m128(float* A, float* B) {
   // CHECK-LABEL: test_mm256_loadu2_m128
   // CHECK: load <4 x float>, <4 x float>* %{{.*}}, align 1{{$}}
-  // CHECK: shufflevector <4 x float> %{{.*}}, <4 x float> %{{.*}}, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 undef, i32 undef, i32 undef, i32 undef>
   // CHECK: load <4 x float>, <4 x float>* %{{.*}}, align 1{{$}}
-  // CHECK: shufflevector <4 x float> %{{.*}}, <4 x float> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
-  // CHECK: shufflevector <8 x float> %{{.*}}, <8 x float> %{{.*}}, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 8, i32 9, i32 10, i32 11>
+  // CHECK: shufflevector <4 x float> %{{.*}}, <4 x float> %{{.*}}, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
   return _mm256_loadu2_m128(A, B);
 }
 
 __m256d test_mm256_loadu2_m128d(double* A, double* B) {
   // CHECK-LABEL: test_mm256_loadu2_m128d
   // CHECK: load <2 x double>, <2 x double>* %{{.*}}, align 1{{$}}
-  // CHECK: shufflevector <2 x double> %{{.*}}, <2 x double> %{{.*}}, <4 x i32> <i32 0, i32 1, i32 undef, i32 undef>
   // CHECK: load <2 x double>, <2 x double>* %{{.*}}, align 1{{$}}
-  // CHECK: shufflevector <2 x double> %{{.*}}, <2 x double> poison, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
-  // CHECK: shufflevector <4 x double> %{{.*}}, <4 x double> %{{.*}}, <4 x i32> <i32 0, i32 1, i32 4, i32 5>
+  // CHECK: shufflevector <2 x double> %{{.*}}, <2 x double> %{{.*}}, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
   return _mm256_loadu2_m128d(A, B);
 }
 
 __m256i test_mm256_loadu2_m128i(__m128i* A, __m128i* B) {
   // CHECK-LABEL: test_mm256_loadu2_m128i
   // CHECK: load <2 x i64>, <2 x i64>* %{{.*}}, align 1{{$}}
-  // CHECK: shufflevector <2 x i64> %{{.*}}, <2 x i64> %{{.*}}, <4 x i32> <i32 0, i32 1, i32 undef, i32 undef>
   // CHECK: load <2 x i64>, <2 x i64>* %{{.*}}, align 1{{$}}
-  // CHECK: shufflevector <4 x i32> %{{.*}}, <4 x i32> poison, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
-  // CHECK: shufflevector <8 x i32> %{{.*}}, <8 x i32> %{{.*}}, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 8, i32 9, i32 10, i32 11>
+  // CHECK: shufflevector <2 x i64> %{{.*}}, <2 x i64> %{{.*}}, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
   return _mm256_loadu2_m128i(A, B);
 }