Refactor SafepointTable and create a chokepoint

... on Code objects.

Refactors: create a dedicated WasmCode constructor, hide the internal
constructor, constify members, and let SafepointTable handle
out-of-line tables.

Expose a new Code::SafepointTableAddress() helper as the source of
truth. Some safepoint tables may move out-of-line in the near future.

Bug: v8:7777,v8:10707
Change-Id: I4e2d954ed2d157235e9dfa3e7a5ca08800896683
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2297459Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68837}

src/codegen/safepoint-table.cc

@@ -10,26 +10,29 @@
 #include "src/diagnostics/disasm.h"
 #include "src/execution/frames-inl.h"
 #include "src/utils/ostreams.h"
+#include "src/wasm/wasm-code-manager.h"
 
 namespace v8 {
 namespace internal {
 
+SafepointTable::SafepointTable(Code code)
+    : SafepointTable(code.InstructionStart(), code.SafepointTableAddress(),
+                     code.stack_slots(), true) {}
+
+SafepointTable::SafepointTable(const wasm::WasmCode* code)
+    : SafepointTable(code->instruction_start(),
+                     code->instruction_start() + code->safepoint_table_offset(),
+                     code->stack_slots(), false) {}
+
 SafepointTable::SafepointTable(Address instruction_start,
-                               size_t safepoint_table_offset,
+                               Address safepoint_table_address,
                                uint32_t stack_slots, bool has_deopt)
     : instruction_start_(instruction_start),
       stack_slots_(stack_slots),
-      has_deopt_(has_deopt) {
-  Address header = instruction_start_ + safepoint_table_offset;
-  length_ = Memory<uint32_t>(header + kLengthOffset);
-  entry_size_ = Memory<uint32_t>(header + kEntrySizeOffset);
-  pc_and_deoptimization_indexes_ = header + kHeaderSize;
-  entries_ = pc_and_deoptimization_indexes_ + (length_ * kFixedEntrySize);
-}
-
-SafepointTable::SafepointTable(Code code)
-    : SafepointTable(code.InstructionStart(), code.safepoint_table_offset(),
-                     code.stack_slots(), true) {}
+      has_deopt_(has_deopt),
+      safepoint_table_address_(safepoint_table_address),
+      length_(ReadLength(safepoint_table_address)),
+      entry_size_(ReadEntrySize(safepoint_table_address)) {}
 
 unsigned SafepointTable::find_return_pc(unsigned pc_offset) {
   for (unsigned i = 0; i < length(); i++) {
@@ -40,7 +43,6 @@ unsigned SafepointTable::find_return_pc(unsigned pc_offset) {
     }
   }
   UNREACHABLE();
-  return 0;
 }
 
 SafepointEntry SafepointTable::FindEntry(Address pc) const {
@@ -60,7 +62,6 @@ SafepointEntry SafepointTable::FindEntry(Address pc) const {
     }
   }
   UNREACHABLE();
-  return SafepointEntry();
 }
 
 void SafepointTable::PrintEntry(unsigned index,

src/codegen/safepoint-table.h

@@ -15,6 +15,10 @@
 namespace v8 {
 namespace internal {
 
+namespace wasm {
+class WasmCode;
+}
+
 class SafepointEntry {
  public:
   SafepointEntry() : deopt_index_(0), bits_(nullptr), trampoline_pc_(-1) {}
@@ -64,9 +68,7 @@ class SafepointEntry {
 class SafepointTable {
  public:
   explicit SafepointTable(Code code);
-  explicit SafepointTable(Address instruction_start,
-                          size_t safepoint_table_offset, uint32_t stack_slots,
-                          bool has_deopt = false);
+  explicit SafepointTable(const wasm::WasmCode* code);
 
   int size() const {
     return kHeaderSize + (length_ * (kFixedEntrySize + entry_size_));
@@ -90,7 +92,7 @@ class SafepointTable {
     DCHECK(index < length_);
     unsigned deopt_index =
         base::Memory<uint32_t>(GetEncodedInfoLocation(index));
-    uint8_t* bits = &base::Memory<uint8_t>(entries_ + (index * entry_size_));
+    uint8_t* bits = &base::Memory<uint8_t>(entries() + (index * entry_size_));
     int trampoline_pc =
         has_deopt_ ? base::Memory<int>(GetTrampolineLocation(index)) : -1;
     return SafepointEntry(deopt_index, bits, trampoline_pc);
@@ -102,9 +104,12 @@ class SafepointTable {
   void PrintEntry(unsigned index, std::ostream& os) const;  // NOLINT
 
  private:
+  SafepointTable(Address instruction_start, Address safepoint_table_address,
+                 uint32_t stack_slots, bool has_deopt);
+
   static const uint8_t kNoRegisters = 0xFF;
 
-  // Layout information
+  // Layout information.
   static const int kLengthOffset = 0;
   static const int kEntrySizeOffset = kLengthOffset + kIntSize;
   static const int kHeaderSize = kEntrySizeOffset + kIntSize;
@@ -113,8 +118,21 @@ class SafepointTable {
   static const int kTrampolinePcOffset = kEncodedInfoOffset + kIntSize;
   static const int kFixedEntrySize = kTrampolinePcOffset + kIntSize;
 
+  static uint32_t ReadLength(Address table) {
+    return base::Memory<uint32_t>(table + kLengthOffset);
+  }
+  static uint32_t ReadEntrySize(Address table) {
+    return base::Memory<uint32_t>(table + kEntrySizeOffset);
+  }
+  Address pc_and_deoptimization_indexes() const {
+    return safepoint_table_address_ + kHeaderSize;
+  }
+  Address entries() const {
+    return safepoint_table_address_ + kHeaderSize + (length_ * kFixedEntrySize);
+  }
+
   Address GetPcOffsetLocation(unsigned index) const {
-    return pc_and_deoptimization_indexes_ + (index * kFixedEntrySize);
+    return pc_and_deoptimization_indexes() + (index * kFixedEntrySize);
   }
 
   Address GetEncodedInfoLocation(unsigned index) const {
@@ -125,18 +143,18 @@ class SafepointTable {
     return GetPcOffsetLocation(index) + kTrampolinePcOffset;
   }
 
-  static void PrintBits(std::ostream& os,  // NOLINT
-                        uint8_t byte, int digits);
+  static void PrintBits(std::ostream& os, uint8_t byte, int digits);
 
   DISALLOW_HEAP_ALLOCATION(no_allocation_)
-  Address instruction_start_;
-  uint32_t stack_slots_;
-  unsigned length_;
-  unsigned entry_size_;
-
-  Address pc_and_deoptimization_indexes_;
-  Address entries_;
-  bool has_deopt_;
+
+  const Address instruction_start_;
+  const uint32_t stack_slots_;
+  const bool has_deopt_;
+
+  // Safepoint table layout.
+  const Address safepoint_table_address_;
+  const uint32_t length_;
+  const uint32_t entry_size_;
 
   friend class SafepointTableBuilder;
   friend class SafepointEntry;

src/execution/frames.cc

@@ -923,9 +923,7 @@ void StandardFrame::IterateCompiledFrame(RootVisitor* v) const {
   bool has_tagged_params = false;
   uint32_t tagged_parameter_slots = 0;
   if (wasm_code != nullptr) {
-    SafepointTable table(wasm_code->instruction_start(),
-                         wasm_code->safepoint_table_offset(),
-                         wasm_code->stack_slots());
+    SafepointTable table(wasm_code);
     safepoint_entry = table.FindEntry(inner_pointer);
     stack_slots = wasm_code->stack_slots();
     has_tagged_params = wasm_code->kind() != wasm::WasmCode::kFunction &&

src/objects/code.cc

@@ -30,6 +30,10 @@
 namespace v8 {
 namespace internal {
 
+Address Code::SafepointTableAddress() const {
+  return InstructionStart() + safepoint_table_offset();
+}
+
 int Code::safepoint_table_size() const {
   DCHECK_GE(handler_table_offset() - safepoint_table_offset(), 0);
   return handler_table_offset() - safepoint_table_offset();

src/objects/code.h

@@ -150,6 +150,7 @@ class Code : public HeapObject {
   // instruction stream where the safepoint table starts.
   inline int safepoint_table_offset() const;
   inline void set_safepoint_table_offset(int offset);
+  Address SafepointTableAddress() const;
   int safepoint_table_size() const;
   bool has_safepoint_table() const;
 

src/wasm/wasm-code-manager.cc

@@ -393,8 +393,7 @@ void WasmCode::Disassemble(const char* name, std::ostream& os,
   }
 
   if (safepoint_table_offset_ > 0) {
-    SafepointTable table(instruction_start(), safepoint_table_offset_,
-                         stack_slots_);
+    SafepointTable table(this);
     os << "Safepoints (size = " << table.size() << ")\n";
     for (uint32_t i = 0; i < table.length(); i++) {
       uintptr_t pc_offset = table.GetPcOffset(i);