X64: Ensure that there is always room for a call between recoreded safepoints.

src/x64/lithium-codegen-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 30 matching lines @@
 // the invoke instruction sequence generated by the macro assembler.
 class SafepointGenerator : public PostCallGenerator {
  public:
   SafepointGenerator(LCodeGen* codegen,
                      LPointerMap* pointers,
                      int deoptimization_index,
                      bool ensure_reloc_space = false)
       : codegen_(codegen),
         pointers_(pointers),
         deoptimization_index_(deoptimization_index),
-        ensure_reloc_space_(ensure_reloc_space) { }
+        ensure_reloc_space_(ensure_reloc_space),
+        previous_safepoint_position_(-kMinSafepointSize) { }
   virtual ~SafepointGenerator() { }
 
   virtual void Generate() {
+    // Ensure that we have enough space after the previous safepoint position
+    // for the generated code there.
+    int position = codegen_->masm()->pc_offset();
+    ASSERT(position > previous_safepoint_position_);
+    if (position < previous_safepoint_position_ + kMinSafepointSize) {
+      int padding_size =
+          previous_safepoint_position_ + kMinSafepointSize - position;
+      STATIC_ASSERT(kMinSafepointSize <= 9);  // One multibyte nop is enough.
+      codegen_->masm()->nop(padding_size);
+      position += padding_size;
+    }
     // Ensure that we have enough space in the reloc info to patch
     // this with calls when doing deoptimization.
     if (ensure_reloc_space_) {
       codegen_->masm()->RecordComment(RelocInfo::kFillerCommentString, true);
     }
     codegen_->RecordSafepoint(pointers_, deoptimization_index_);
+    previous_safepoint_position_ = position;
   }
 
  private:
+  static const int kMinSafepointSize =
+      MacroAssembler::kShortCallInstructionLength;
   LCodeGen* codegen_;
   LPointerMap* pointers_;
   int deoptimization_index_;
   bool ensure_reloc_space_;
+  int previous_safepoint_position_;
 };
 
 
 #define __ masm()->
 
 bool LCodeGen::GenerateCode() {
   HPhase phase("Code generation", chunk());
   ASSERT(is_unused());
   status_ = GENERATING;
   return GeneratePrologue() &&
@@ skipping 3569 matching lines @@
   RegisterEnvironmentForDeoptimization(environment);
   ASSERT(osr_pc_offset_ == -1);
   osr_pc_offset_ = masm()->pc_offset();
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64