[Liftoff] Runtime call arguments are always on the stack

This removes dead code handling register arguments to runtime calls,
which do not exist currently.

R=mstarzinger@chromium.org

Change-Id: Ia5fdd60d0036f87a335bbe42b5790d1b86aa0add
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1715448Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62889}

src/wasm/baseline/liftoff-compiler.cc

@@ -1606,26 +1606,23 @@ class LiftoffCompiler {
 
   void GenerateRuntimeCall(Runtime::FunctionId runtime_function, int num_args,
                            Register* args) {
-    auto call_descriptor = compiler::Linkage::GetRuntimeCallDescriptor(
-        compilation_zone_, runtime_function, num_args,
-        compiler::Operator::kNoProperties, compiler::CallDescriptor::kNoFlags);
     // Currently, only one argument is supported. More arguments require some
     // caution for the parallel register moves (reuse StackTransferRecipe).
     DCHECK_EQ(1, num_args);
+#ifdef DEBUG
+    auto call_descriptor = compiler::Linkage::GetRuntimeCallDescriptor(
+        compilation_zone_, runtime_function, num_args,
+        compiler::Operator::kNoProperties, compiler::CallDescriptor::kNoFlags);
     constexpr size_t kInputShift = 1;  // Input 0 is the call target.
     compiler::LinkageLocation param_loc =
         call_descriptor->GetInputLocation(kInputShift);
-    if (param_loc.IsRegister()) {
-      Register reg = Register::from_code(param_loc.AsRegister());
-      __ Move(LiftoffRegister(reg), LiftoffRegister(args[0]),
-              LiftoffAssembler::kWasmIntPtr);
-    } else {
-      DCHECK(param_loc.IsCallerFrameSlot());
-      LiftoffStackSlots stack_slots(&asm_);
-      stack_slots.Add(LiftoffAssembler::VarState(LiftoffAssembler::kWasmIntPtr,
-                                                 LiftoffRegister(args[0])));
-      stack_slots.Construct();
-    }
+    // Runtime calls take their arguments on the stack.
+    DCHECK(param_loc.IsCallerFrameSlot());
+#endif
+    LiftoffStackSlots stack_slots(&asm_);
+    stack_slots.Add(LiftoffAssembler::VarState(LiftoffAssembler::kWasmIntPtr,
+                                               LiftoffRegister(args[0])));
+    stack_slots.Construct();
 
     // Set context to "no context" for the runtime call.
     __ TurboAssembler::Move(kContextRegister,