[wasm] simd scalar lowering F32x4Add and I32x4Add

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 025ccdf1d7bfc0d2c159e511600b0d313cf0fa9b..a9282841d6b8716d1b55e8f7a5cd43ffef55735b 100644
--- a/src/wasm/ast-decoder.cc
+++ b/src/wasm/ast-decoder.cc
@@ -241,7 +241,8 @@ class WasmDecoder : public Decoder {
   }
 
   unsigned OpcodeLength(const byte* pc) {
-    switch (static_cast<WasmOpcode>(*pc)) {
+    WasmOpcode opcode = ExtractWasmOpcode(pc);

[titzer, 2016/10/12 19:06:55]

Could you do the trick in the main decoder loop of making the SIMD prefix one of
the cases here, so we save a branch in the common case?

[aseemgarg, 2016/10/17 19:01:44]

Done. Actually seems like we don't need this at all.

[titzer, 2016/10/19 18:31:49]

No, you do, since we still want to be able to iterate over SIMD bytecodes, which
are not a single byte.

[aseemgarg, 2016/10/19 23:37:33]

Done.

+    switch (opcode) {
 #define DECLARE_OPCODE_CASE(name, opcode, sig) case kExpr##name:
       FOREACH_LOAD_MEM_OPCODE(DECLARE_OPCODE_CASE)
       FOREACH_STORE_MEM_OPCODE(DECLARE_OPCODE_CASE)
@@ -308,6 +309,15 @@ class WasmDecoder : public Decoder {
         return 1;
     }
   }
+
+ private:
+  WasmOpcode ExtractWasmOpcode(const byte* pc) {
+    WasmOpcode opcode = static_cast<WasmOpcode>(*pc);
+    if (opcode == kSimdPrefix) {
+      opcode = static_cast<WasmOpcode>((opcode << 8) | *(pc + 1));
+    }
+    return opcode;
+  }
 };
 
 static const int32_t kNullCatch = -1;
@@ -1248,18 +1258,28 @@ class WasmFullDecoder : public WasmDecoder {
     return 1 + operand.length;
   }
 
+  unsigned ExtractLane(WasmOpcode opcode, LocalType type) {

[titzer, 2016/10/12 19:06:55]

Please make a LaneOperand class similar to the others in wasm-opcodes.h

I think you can keep it in the .cc file for now, though.

[aseemgarg, 2016/10/17 19:01:44]

Done.

+    unsigned len = 0;
+    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);
+    Push(type, node);
+    len++;
+    return len;
+  }
+
   unsigned DecodeSimdOpcode(WasmOpcode opcode) {
     unsigned len = 0;
     switch (opcode) {
       case kExprI32x4ExtractLane: {
-        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);
-        Push(LocalType::kWord32, node);
-        len++;
+        len = ExtractLane(opcode, LocalType::kWord32);
+        break;
+      }
+      case kExprF32x4ExtractLane: {
+        len = ExtractLane(opcode, LocalType::kFloat32);
         break;
       }
       default: {