ARM: Clean up literal pool generation....

src/arm/assembler-arm.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 1140 matching lines @@
     ~BlockConstPoolScope() {
       assem_->EndBlockConstPool();
     }
 
    private:
     Assembler* assem_;
 
     DISALLOW_IMPLICIT_CONSTRUCTORS(BlockConstPoolScope);
   };
 
-  // Postpone the generation of the constant pool for the specified number of
-  // instructions.
-  void BlockConstPoolFor(int instructions);
-
   // Debugging
 
   // Mark address of the ExitJSFrame code.
   void RecordJSReturn();
 
   // Mark address of a debug break slot.
   void RecordDebugBreakSlot();
 
   // Record the AST id of the CallIC being compiled, so that it can be placed
   // in the relocation information.
@@ skipping 39 matching lines @@
   static bool IsStrRegFpNegOffset(Instr instr);
   static bool IsLdrRegFpNegOffset(Instr instr);
   static bool IsLdrPcImmediateOffset(Instr instr);
   static bool IsTstImmediate(Instr instr);
   static bool IsCmpRegister(Instr instr);
   static bool IsCmpImmediate(Instr instr);
   static Register GetCmpImmediateRegister(Instr instr);
   static int GetCmpImmediateRawImmediate(Instr instr);
   static bool IsNop(Instr instr, int type = NON_MARKING_NOP);
 
-  // Buffer size and constant pool distance are checked together at regular
-  // intervals of kBufferCheckInterval emitted bytes
-  static const int kBufferCheckInterval = 1*KB/2;
   // Constants in pools are accessed via pc relative addressing, which can
   // reach +/-4KB thereby defining a maximum distance between the instruction
-  // and the accessed constant. We satisfy this constraint by limiting the
-  // distance between pools.
-  static const int kMaxDistBetweenPools = 4*KB - 2*kBufferCheckInterval;
-  static const int kMaxNumPRInfo = kMaxDistBetweenPools/kInstrSize;
+  // and the accessed constant.
+  static const int kMaxDistToPool = 4*KB;
+  static const int kMaxNumPRInfo = kMaxDistToPool/kInstrSize;
 
-  // Check if is time to emit a constant pool for pending reloc info entries
+  // Postpone the generation of the constant pool for the specified number of
+  // instructions.
+  void BlockConstPoolFor(int instructions);
+
+  // Check if is time to emit a constant pool.
   void CheckConstPool(bool force_emit, bool require_jump);
 
  protected:
   // Relocation for a type-recording IC has the AST id added to it.  This
   // member variable is a way to pass the information from the call site to
   // the relocation info.
   unsigned ast_id_for_reloc_info_;
 
   bool emit_debug_code() const { return emit_debug_code_; }
 
   int buffer_space() const { return reloc_info_writer.pos() - pc_; }
 
   // Read/patch instructions
   Instr instr_at(int pos) { return *reinterpret_cast<Instr*>(buffer_ + pos); }
   void instr_at_put(int pos, Instr instr) {
     *reinterpret_cast<Instr*>(buffer_ + pos) = instr;
   }
 
   // Decode branch instruction at pos and return branch target pos
   int target_at(int pos);
 
   // Patch branch instruction at pos to branch to given branch target pos
   void target_at_put(int pos, int target_pos);
 
-  // Block the emission of the constant pool before pc_offset
-  void BlockConstPoolBefore(int pc_offset) {
-    if (no_const_pool_before_ < pc_offset) no_const_pool_before_ = pc_offset;
+  // Prevent contant pool emission until EndBlockConstPool is called.
+  // Call to this function can be nested but must be followed by an equal
+  // number of call to EndBlockConstpool.
+  void StartBlockConstPool() {
+    if (const_pool_blocked_nesting_++ == 0) {
+      // Prevent constant pool checks happening by setting the next check to
+      // the biggest possible offset.
+      next_buffer_check_ = kMaxInt;
+    }
   }
 
-  void StartBlockConstPool() {
-    const_pool_blocked_nesting_++;
+  // Resume constant pool emission. Need to be called as many time as
+  // StartBlockConstPool to have an effect.
+  void EndBlockConstPool() {
+    if (--const_pool_blocked_nesting_ == 0) {
+      // Check the constant pool hasn't been blocked for too long.
+      ASSERT((num_prinfo_ == 0) ||
+             (pc_offset() < (first_const_pool_use_ + kMaxDistToPool)));
+      // Two cases:
+      //  * no_const_pool_before_ >= next_buffer_check_ and the emission is
+      //    still blocked
+      //  * no_const_pool_before_ < next_buffer_check_ and the next emit will
+      //    trigger a check.
+      next_buffer_check_ = no_const_pool_before_;
+    }
   }
-  void EndBlockConstPool() {
-    const_pool_blocked_nesting_--;
+
+  bool is_const_pool_blocked() const {
+    return (const_pool_blocked_nesting_ > 0) ||
+           (pc_offset() < no_const_pool_before_);
   }
-  bool is_const_pool_blocked() const { return const_pool_blocked_nesting_ > 0; }
 
  private:
   // Code buffer:
   // The buffer into which code and relocation info are generated.
   byte* buffer_;
   int buffer_size_;
   // True if the assembler owns the buffer, false if buffer is external.
   bool own_buffer_;
 
   int next_buffer_check_;  // pc offset of next buffer check
@@ skipping 13 matching lines @@
   // necessary to emit the constant pool before the pool gets too far from the
   // location it is accessed from. In this case, we emit a jump over the emitted
   // constant pool.
   // Constants in the pool may be addresses of functions that gets relocated;
   // if so, a relocation info entry is associated to the constant pool entry.
 
   // Repeated checking whether the constant pool should be emitted is rather
   // expensive. By default we only check again once a number of instructions
   // has been generated. That also means that the sizing of the buffers is not
   // an exact science, and that we rely on some slop to not overrun buffers.
-  static const int kCheckConstIntervalInst = 32;
-  static const int kCheckConstInterval = kCheckConstIntervalInst * kInstrSize;
+  static const int kCheckPoolIntervalInst = 32;
+  static const int kCheckPoolInterval = kCheckPoolIntervalInst * kInstrSize;
 
 
-  // Pools are emitted after function return and in dead code at (more or less)
-  // regular intervals of kDistBetweenPools bytes
-  static const int kDistBetweenPools = 1*KB;
+  // Average distance beetween a constant pool and the first instruction
+  // accessing the constant pool. Longer distance should result in less I-cache
+  // pollution.
+  // In practice the distance will be smaller since constant pool emission is
+  // forced after function return and sometimes after unconditional branches.
+  static const int kAvgDistToPool = kMaxDistToPool - kCheckPoolInterval;
 
   // Emission of the constant pool may be blocked in some code sequences.
   int const_pool_blocked_nesting_;  // Block emission if this is not zero.
   int no_const_pool_before_;  // Block emission before this pc offset.
 
-  // Keep track of the last emitted pool to guarantee a maximal distance
-  int last_const_pool_end_;  // pc offset following the last constant pool
+  // Keep track of the first instruction requiring a constant pool entry
+  // since the previous constant pool was emitted.
+  int first_const_pool_use_;
 
   // Relocation info generation
   // Each relocation is encoded as a variable size value
   static const int kMaxRelocSize = RelocInfoWriter::kMaxSize;
   RelocInfoWriter reloc_info_writer;
   // Relocation info records are also used during code generation as temporary
   // containers for constants and code target addresses until they are emitted
   // to the constant pool. These pending relocation info records are temporarily
   // stored in a separate buffer until a constant pool is emitted.
   // If every instruction in a long sequence is accessing the pool, we need one
@@ skipping 41 matching lines @@
  public:
   explicit EnsureSpace(Assembler* assembler) {
     assembler->CheckBuffer();
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM_ASSEMBLER_ARM_H_