[liftoff] API for exposing frame slot count

Factor out slot count calculation, and expose it so it may later be
consumed when JIT-ing to the WasmCodeManager.

Bug: 
Change-Id: I21d673b2e3d7fa4a66ae0ab6303d29cf666d743c
Reviewed-on: https://chromium-review.googlesource.com/782701Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49556}

src/wasm/baseline/liftoff-assembler.cc

@@ -387,6 +387,10 @@ void LiftoffAssembler::set_num_locals(uint32_t num_locals) {
   }
 }
 
+uint32_t LiftoffAssembler::GetTotalFrameSlotCount() const {
+  return kPointerSize * (num_locals() + kMaxValueStackHeight);
+}
+
 #undef __
 #undef TRACE
 

src/wasm/baseline/liftoff-assembler.h

@@ -48,6 +48,10 @@ constexpr ValueType kWasmPtrSizeInt = kPointerSize == 8 ? kWasmI64 : kWasmI32;
 
 class LiftoffAssembler : public TurboAssembler {
  public:
+  // TODO(clemensh): Remove this limitation by allocating more stack space if
+  // needed.
+  static constexpr int kMaxValueStackHeight = 8;
+
   class PinnedRegisterScope {
    public:
     PinnedRegisterScope() : pinned_regs_(0) {}
@@ -266,6 +270,9 @@ class LiftoffAssembler : public TurboAssembler {
   uint32_t num_locals() const { return num_locals_; }
   void set_num_locals(uint32_t num_locals);
 
+  uint32_t GetTotalFrameSlotCount() const;
+  size_t GetSafepointTableOffset() const { return 0; }
+
   ValueType local_type(uint32_t index) {
     DCHECK_GT(num_locals_, index);
     ValueType* locals =

src/wasm/baseline/liftoff-compiler.cc

@@ -79,7 +79,7 @@ class LiftoffCompiler {
   void CheckStackSizeLimit(Decoder* decoder) {
     DCHECK_GE(__ cache_state()->stack_height(), __ num_locals());
     int stack_height = __ cache_state()->stack_height() - __ num_locals();
-    if (stack_height > kMaxValueStackHeight) {
+    if (stack_height > LiftoffAssembler::kMaxValueStackHeight) {
       unsupported(decoder, "value stack grows too large");
     }
   }
@@ -98,8 +98,7 @@ class LiftoffCompiler {
       return;
     }
     __ EnterFrame(StackFrame::WASM_COMPILED);
-    __ ReserveStackSpace(kPointerSize *
-                         (__ num_locals() + kMaxValueStackHeight));
+    __ ReserveStackSpace(__ GetTotalFrameSlotCount());
     // Parameter 0 is the wasm context.
     uint32_t num_params =
         static_cast<uint32_t>(call_desc_->ParameterCount()) - 1;
@@ -481,10 +480,6 @@ class LiftoffCompiler {
   compiler::CallDescriptor* call_desc_;
   compiler::ModuleEnv* env_;
   bool ok_ = true;
-
-  // TODO(clemensh): Remove this limitation by allocating more stack space if
-  // needed.
-  static constexpr int kMaxValueStackHeight = 8;
 };
 
 }  // namespace