[wasm] Reuse simple operator logic

We already have specialized logic for unops and binops, and the generic
{BuildSimpleOperator} implementation (based on a signature) was
reimplementing these two cases.
This CL avoids the switch since we only need to handle exactly two
cases, and redirects to the existing methods for implementing them.

R=thibaudm@chromium.org

Bug: v8:10576
Change-Id: I8eb5c768f0fa59e48503c108498b334a0ae9037a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2249859Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68456}

src/wasm/function-body-decoder-impl.h

@@ -3822,24 +3822,13 @@ class WasmFullDecoder : public WasmDecoder<validate> {
   }
 
   void BuildSimpleOperator(WasmOpcode opcode, const FunctionSig* sig) {
-    switch (sig->parameter_count()) {
-      case 1: {
-        Value val = Pop(0, sig->GetParam(0));
-        Value* ret =
-            sig->return_count() == 0 ? nullptr : Push(sig->GetReturn(0));
-        CALL_INTERFACE_IF_REACHABLE(UnOp, opcode, val, ret);
-        break;
-      }
-      case 2: {
-        Value rval = Pop(1, sig->GetParam(1));
-        Value lval = Pop(0, sig->GetParam(0));
-        Value* ret =
-            sig->return_count() == 0 ? nullptr : Push(sig->GetReturn(0));
-        CALL_INTERFACE_IF_REACHABLE(BinOp, opcode, lval, rval, ret);
-        break;
-      }
-      default:
-        UNREACHABLE();
+    DCHECK_GE(1, sig->return_count());
+    ValueType ret = sig->return_count() == 0 ? kWasmStmt : sig->GetReturn(0);
+    if (sig->parameter_count() == 1) {
+      BuildSimpleOperator(opcode, ret, sig->GetParam(0));
+    } else {
+      DCHECK_EQ(2, sig->parameter_count());
+      BuildSimpleOperator(opcode, ret, sig->GetParam(0), sig->GetParam(1));
     }
   }