[wasm] Add simd lowering for I16x8Neg

BUG=

Review-Url: https://codereview.chromium.org/2861113002
Cr-Commit-Position: refs/heads/master@{#45320}

src/compiler/simd-scalar-lowering.cc

@@ -834,15 +834,20 @@ void SimdScalarLowering::LowerNode(Node* node) {
       LowerIntMinMax(node, machine()->Uint32LessThan(), false, rep_type);
       break;
     }
-    case IrOpcode::kI32x4Neg: {
+    case IrOpcode::kI32x4Neg:
+    case IrOpcode::kI16x8Neg: {
       DCHECK(node->InputCount() == 1);
       Node** rep = GetReplacementsWithType(node->InputAt(0), rep_type);
-      Node* rep_node[kNumLanes32];
+      int num_lanes = NumLanes(rep_type);
+      Node** rep_node = zone()->NewArray<Node*>(num_lanes);
       Node* zero = graph()->NewNode(common()->Int32Constant(0));
-      for (int i = 0; i < kNumLanes32; ++i) {
+      for (int i = 0; i < num_lanes; ++i) {
         rep_node[i] = graph()->NewNode(machine()->Int32Sub(), zero, rep[i]);
+        if (node->opcode() == IrOpcode::kI16x8Neg) {
+          rep_node[i] = FixUpperBits(rep_node[i], kShift16);
+        }
       }
-      ReplaceNode(node, rep_node, kNumLanes32);
+      ReplaceNode(node, rep_node, num_lanes);
       break;
     }
     case IrOpcode::kS128Not: {

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

@@ -1161,7 +1161,8 @@ WASM_EXEC_COMPILED_TEST(I16x8ConvertI8x16) {
 }
 #endif  // V8_TARGET_ARCH_ARM
 
-#if V8_TARGET_ARCH_ARM || V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64
+#if SIMD_LOWERING_TARGET || V8_TARGET_ARCH_ARM || V8_TARGET_ARCH_MIPS || \
+    V8_TARGET_ARCH_MIPS64
 void RunI16x8UnOpTest(WasmOpcode simd_op, Int16UnOp expected_op) {
   FLAG_wasm_simd_prototype = true;
   WasmRunner<int32_t, int32_t, int32_t> r(kExecuteCompiled);
@@ -1176,7 +1177,8 @@ void RunI16x8UnOpTest(WasmOpcode simd_op, Int16UnOp expected_op) {
 }
 
 WASM_EXEC_COMPILED_TEST(I16x8Neg) { RunI16x8UnOpTest(kExprI16x8Neg, Negate); }
-#endif  // V8_TARGET_ARCH_ARM || V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64
+#endif  // SIMD_LOWERING_TARGET || V8_TARGET_ARCH_ARM || V8_TARGET_ARCH_MIPS ||
+        // V8_TARGET_ARCH_MIPS64
 
 #if V8_TARGET_ARCH_ARM
 // Tests both signed and unsigned conversion from I32x4 (packing).