[wasm-simd][scalar-lowering] Fix splats for i8 and i16

i8 and i16 nodes are stored in word32 nodes, when splat-ing them, we
need to make sure to handle overflow values and also sign extend them
correctly.

This fix allows us to pass simd-splat.js. It still fails on ARM
(non-simulator) due to a use of f32x4.min in the test.

Bug: v8:10507
Change-Id: I1507637a7edb33a530c84c85ee8d4acb481293e2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2430170Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70146}

src/compiler/simd-scalar-lowering.cc

@@ -1837,12 +1837,22 @@ void SimdScalarLowering::LowerNode(Node* node) {
     case IrOpcode::kI16x8Splat:
     case IrOpcode::kI8x16Splat: {
       Node** rep_node = zone()->NewArray<Node*>(num_lanes);
-      for (int i = 0; i < num_lanes; ++i) {
-        if (HasReplacement(0, node->InputAt(0))) {
-          rep_node[i] = GetReplacements(node->InputAt(0))[0];
-        } else {
-          rep_node[i] = node->InputAt(0);
+      Node* val = (HasReplacement(0, node->InputAt(0)))
+                      ? GetReplacements(node->InputAt(0))[0]
+                      : node->InputAt(0);
+
+      // I16 and I8 are placed in Word32 nodes, we need to mask them
+      // accordingly, to account for overflows, then sign extend them.
+      if (node->opcode() == IrOpcode::kI16x8Splat) {
+        val = graph()->NewNode(machine()->SignExtendWord16ToInt32(),
+                               Mask(val, kMask16));
+      } else if (node->opcode() == IrOpcode::kI8x16Splat) {
+        val = graph()->NewNode(machine()->SignExtendWord8ToInt32(),
+                               Mask(val, kMask8));
       }
+
+      for (int i = 0; i < num_lanes; ++i) {
+        rep_node[i] = val;
       }
       ReplaceNode(node, rep_node, num_lanes);
       break;
@@ -1861,6 +1871,7 @@ void SimdScalarLowering::LowerNode(Node* node) {
       for (int i = 1; i < num_lanes; ++i) {
         rep_node[i] = nullptr;
       }
+
       ReplaceNode(node, rep_node, num_lanes);
       break;
     }

test/wasm-spec-tests/wasm-spec-tests.status

@@ -43,7 +43,6 @@
   'proposals/simd/simd_conversions' : [PASS, FAIL],
   'proposals/simd/simd_lane' : [PASS, FAIL],
   'proposals/simd/simd_load_splat' : [PASS, FAIL],
-  'proposals/simd/simd_splat' : [PASS, FAIL],
 
 }],  # ALWAYS
 
@@ -52,6 +51,9 @@
   'proposals/simd/simd_f32x4': [PASS, FAIL],
   'proposals/simd/simd_f32x4_arith': [PASS, FAIL],
   'proposals/simd/simd_f32x4_cmp': [PASS, FAIL],
+  # This test only has 1 problematic use of f32x4.min and f32x4.div, consider
+  # removing it from upstream, then we can run this test.
+  'proposals/simd/simd_splat' : [PASS, FAIL],
 }],  # arch == arm and not simulator_run
 
 ['arch == mipsel or arch == mips64el or arch == mips or arch == mips64', {