[wasm] Implement I32x4ReplaceLane, I32x4Add, I32x4Sub.

src/wasm/ast-decoder.cc

Index: src/wasm/ast-decoder.cc
diff --git a/src/wasm/ast-decoder.cc b/src/wasm/ast-decoder.cc
index 02d1db5bdad3b38998b0fd5b11e75c6202c58eab..9fabff9b578291ae98bc12bf650131854ce1cac0 100644
--- a/src/wasm/ast-decoder.cc
+++ b/src/wasm/ast-decoder.cc
@@ -1248,13 +1248,29 @@ class WasmFullDecoder : public WasmDecoder {
   unsigned DecodeSimdOpcode(WasmOpcode opcode) {
     unsigned len = 0;
     switch (opcode) {
+      case kExprI32x4ReplaceLane: {
+        compiler::NodeVector inputs(3, zone_);
+        inputs[2] = Pop(1, LocalType::kWord32).node;
+        uint8_t lane = this->checked_read_u8(pc_, 2, "lane number");
+        if (lane < 0 || lane > 3) {
+          error(pc_, pc_ + 2, "invalid extract lane value");

[bbudge, 2016/10/04 20:34:26]

s/extract/replace

I think there are enough SIMD instructions that take immediate values for lanes
that it would be worthwhile to extract a helper method to read an immediate
value, range check, and create the Int32Constant input. This will eliminate a
lot of repetitive code. The only downside is that the error message would have
to be more generic, e.g. "invalid immediate value" but I think the error message
and pc information is enough information.

Also, you should clamp out-of-range values to the legal range here so we don't
have to worry about weird behavior in the assembler. Or does the call to 'error'
make that unnecessary?

[gdeepti, 2016/11/22 01:15:20]

Using LaneOperand as introduced in the ScalarLowering pass that introduces
LaneOperand. The validate function verifies that the lane values are in the
right range. I think error returns a decode error so it does not go to the
assembler. 

+        }
+        inputs[1] = builder_->Int32Constant(lane);
+        inputs[0] = Pop(0, LocalType::kSimd128).node;
+        TFNode* node = BUILD(SimdOp, opcode, inputs);
+        Push(LocalType::kSimd128, node);
+        len++;
+        break;
+      }
       case kExprI32x4ExtractLane: {
+        compiler::NodeVector inputs(2, zone_);
+        inputs[0] = Pop(0, LocalType::kSimd128).node;
         uint8_t lane = this->checked_read_u8(pc_, 2, "lane number");
         if (lane < 0 || lane > 3) {
           error(pc_, pc_ + 2, "invalid extract lane value");
         }
-        TFNode* input = Pop(0, LocalType::kSimd128).node;
-        TFNode* node = BUILD(SimdExtractLane, opcode, lane, input);
+        inputs[1] = builder_->Int32Constant(lane);
+        TFNode* node = BUILD(SimdOp, opcode, inputs);
         Push(LocalType::kWord32, node);
         len++;
         break;