[wasm-simd] Implement load_splat in interpreter

Bug: v8:9886
Change-Id: I860bea0c317e9666662329e9b36598952c8ecfad
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1919697
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65050}

src/wasm/wasm-interpreter.cc

@@ -2644,11 +2644,41 @@ class ThreadImpl {
         QFM_CASE(F64x2Qfma, f64x2, float2, 2, +)
         QFM_CASE(F64x2Qfms, f64x2, float2, 2, -)
 #undef QFM_CASE
+      case kExprS8x16LoadSplat: {
+        return DoSimdLoadSplat<int16, int32_t, int8_t>(
+            decoder, code, pc, len, MachineRepresentation::kWord8);
+      }
+      case kExprS16x8LoadSplat: {
+        return DoSimdLoadSplat<int8, int32_t, int16_t>(
+            decoder, code, pc, len, MachineRepresentation::kWord16);
+      }
+      case kExprS32x4LoadSplat: {
+        return DoSimdLoadSplat<int4, int32_t, int32_t>(
+            decoder, code, pc, len, MachineRepresentation::kWord32);
+      }
+      case kExprS64x2LoadSplat: {
+        return DoSimdLoadSplat<int2, int64_t, int64_t>(
+            decoder, code, pc, len, MachineRepresentation::kWord64);
+      }
       default:
         return false;
     }
   }
 
+  template <typename s_type, typename result_type, typename load_type>
+  bool DoSimdLoadSplat(Decoder* decoder, InterpreterCode* code, pc_t pc,
+                       int* const len, MachineRepresentation rep) {
+    if (!ExecuteLoad<result_type, load_type>(decoder, code, pc, len, rep,
+                                             /*prefix_len=*/1)) {
+      return false;
+    }
+    result_type v = Pop().to<result_type>();
+    s_type s;
+    for (size_t i = 0; i < arraysize(s.val); i++) s.val[i] = v;
+    Push(WasmValue(Simd128(s)));
+    return true;
+  }
+
   // Check if our control stack (frames_) exceeds the limit. Trigger stack
   // overflow if it does, and unwinding the current frame.
   // Returns true if execution can continue, false if the current activation was

test/cctest/wasm/test-run-wasm-simd.cc

@@ -3277,10 +3277,6 @@ WASM_SIMD_TEST(SimdLoadStoreLoadMemargOffset) {
 template <typename T>
 void RunLoadSplatTest(ExecutionTier execution_tier, LowerSimd lower_simd,
                       WasmOpcode op) {
-  if (execution_tier == ExecutionTier::kInterpreter) {
-    // TODO(zhin): implement for interpreter
-    return;
-  }
   constexpr int lanes = 16 / sizeof(T);
   constexpr int mem_index = 16;  // Load from mem index 16 (bytes).
   WasmRunner<int32_t> r(execution_tier, lower_simd);