[Executor] Fix extra branch in addfunc (WasmEdge#1587)

* check the first item and dispatch it to different loops

Signed-off-by: eat4toast <[email protected]>

lib/executor/instantiate/function.cpp

@@ -18,13 +18,24 @@ Expect<void> Executor::instantiate(Runtime::Instance::ModuleInstance &ModInst,
   auto TypeIdxs = FuncSec.getContent();
   auto CodeSegs = CodeSec.getContent();
 
-  // Iterate through the code segments to instantiate function instances.
-  for (uint32_t I = 0; I < CodeSegs.size(); ++I) {
-    // Create and add the function instance into the module instance.
-    auto *FuncType = *ModInst.getFuncType(TypeIdxs[I]);
-    if (auto Symbol = CodeSegs[I].getSymbol()) {
+  if (CodeSegs.size() == 0) {
+    return {};
+  }
+  // The module will always choose the `for` loop in `else` case under
+  // interpreter mode. Instead, if we do branch in the `for` loop which might
+  // cause meaningless branch misses. Therefore we should check the first item
+  // and dispatch it into different cases to reduce branch misses.
+  if (CodeSegs[0].getSymbol() != false) {
+    for (uint32_t I = 0; I < CodeSegs.size(); ++I) {
+      auto *FuncType = *ModInst.getFuncType(TypeIdxs[I]);
+      auto Symbol = CodeSegs[I].getSymbol();
       ModInst.addFunc(&ModInst, *FuncType, std::move(Symbol));
-    } else {
+    }
+  } else {
+    // Iterate through the code segments to instantiate function instances.
+    for (uint32_t I = 0; I < CodeSegs.size(); ++I) {
+      // Create and add the function instance into the module instance.
+      auto *FuncType = *ModInst.getFuncType(TypeIdxs[I]);
       ModInst.addFunc(&ModInst, *FuncType, CodeSegs[I].getLocals(),
                       CodeSegs[I].getExpr().getInstrs());
     }