Optimize memset to pure SIMD because compilers generate consistently bad code. clang for ARM and gcc for x86 https://gcc.godbolt.org/z/oxeGG7aEx

PiperOrigin-RevId: 383467656

2 files changed, 15 insertions, 1 deletions

diff --git a/snappy-internal.h b/snappy-internal.h
index ad2b36a..f1aafa9 100644
--- a/snappy-internal.h
+++ b/snappy-internal.h
@@ -56,6 +56,9 @@ inline void V128_StoreU(V128* dst, V128 val);
 // Each packed integer in the shuffle mask must be in [0,16).
 inline V128 V128_Shuffle(V128 input, V128 shuffle_mask);
 
+// Constructs V128 with 16 chars |c|.
+inline V128 V128_DupChar(char c);
+
 #if SNAPPY_HAVE_SSSE3
 inline V128 V128_Load(const V128* src) { return _mm_load_si128(src); }
 
@@ -66,6 +69,9 @@ inline void V128_StoreU(V128* dst, V128 val) { _mm_storeu_si128(dst, val); }
 inline V128 V128_Shuffle(V128 input, V128 shuffle_mask) {
   return _mm_shuffle_epi8(input, shuffle_mask);
 }
+
+inline V128 V128_DupChar(char c) { return _mm_set1_epi8(c); }
+
 #else
 inline V128 V128_Load(const V128* src) {
   return vld1q_u8(reinterpret_cast<const uint8_t*>(src));
@@ -83,6 +89,8 @@ inline V128 V128_Shuffle(V128 input, V128 shuffle_mask) {
   assert(vminvq_u8(shuffle_mask) >= 0 && vmaxvq_u8(shuffle_mask) <= 15);
   return vqtbl1q_u8(input, shuffle_mask);
 }
+
+inline V128 V128_DupChar(char c) { return vdupq_n_u8(c); }
 #endif
 #endif  // SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
 
diff --git a/snappy.cc b/snappy.cc
index 7d0ff71..632ab85 100644
--- a/snappy.cc
+++ b/snappy.cc
@@ -80,6 +80,7 @@ using internal::V128_Load;
 using internal::V128_LoadU;
 using internal::V128_Shuffle;
 using internal::V128_StoreU;
+using internal::V128_DupChar;
 #endif
 
 // We translate the information encoded in a tag through a lookup table to a
@@ -308,7 +309,12 @@ static inline bool Copy64BytesWithPatternExtension(char* dst, size_t offset) {
       case 0:
         return false;
       case 1: {
-        std::memset(dst, dst[-1], 64);
+        // TODO: Ideally we should memset, move back once the
+        // codegen issues are fixed.
+        V128 pattern = V128_DupChar(dst[-1]);
+        for (int i = 0; i < 4; i++) {
+          V128_StoreU(reinterpret_cast<V128*>(dst + 16 * i), pattern);
+        }
         return true;
       }
       case 2: