Avoid flushing the icache unnecessarily when updating target addresses in code.

src/arm/assembler-arm-inl.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 124 matching lines @@
     return Assembler::target_pointer_address_at(pc_);
   }
 }
 
 
 int RelocInfo::target_address_size() {
   return kPointerSize;
 }
 
 
-void RelocInfo::set_target_address(Address target, WriteBarrierMode mode) {
+void RelocInfo::set_target_address(Address target,
+                                   WriteBarrierMode write_barrier_mode,
+                                   ICacheFlushMode icache_flush_mode) {
   ASSERT(IsCodeTarget(rmode_) || IsRuntimeEntry(rmode_));
-  Assembler::set_target_address_at(pc_, host_, target);
-  if (mode == UPDATE_WRITE_BARRIER && host() != NULL && IsCodeTarget(rmode_)) {
+  Assembler::set_target_address_at(pc_, host_, target, icache_flush_mode);
+  if (write_barrier_mode == UPDATE_WRITE_BARRIER &&
+      host() != NULL && IsCodeTarget(rmode_)) {
     Object* target_code = Code::GetCodeFromTargetAddress(target);
     host()->GetHeap()->incremental_marking()->RecordWriteIntoCode(
         host(), this, HeapObject::cast(target_code));
   }
 }
 
 
 Object* RelocInfo::target_object() {
   ASSERT(IsCodeTarget(rmode_) || rmode_ == EMBEDDED_OBJECT);
   return reinterpret_cast<Object*>(Assembler::target_address_at(pc_, host_));
 }
 
 
 Handle<Object> RelocInfo::target_object_handle(Assembler* origin) {
   ASSERT(IsCodeTarget(rmode_) || rmode_ == EMBEDDED_OBJECT);
   return Handle<Object>(reinterpret_cast<Object**>(
       Assembler::target_address_at(pc_, host_)));
 }
 
 
-void RelocInfo::set_target_object(Object* target, WriteBarrierMode mode) {
+void RelocInfo::set_target_object(Object* target,
+                                  WriteBarrierMode write_barrier_mode,
+                                  ICacheFlushMode icache_flush_mode) {
   ASSERT(IsCodeTarget(rmode_) || rmode_ == EMBEDDED_OBJECT);
   ASSERT(!target->IsConsString());
   Assembler::set_target_address_at(pc_, host_,
-                                   reinterpret_cast<Address>(target));
-  if (mode == UPDATE_WRITE_BARRIER &&
+                                   reinterpret_cast<Address>(target),
+                                   icache_flush_mode);
+  if (write_barrier_mode == UPDATE_WRITE_BARRIER &&
       host() != NULL &&
       target->IsHeapObject()) {
     host()->GetHeap()->incremental_marking()->RecordWrite(
         host(), &Memory::Object_at(pc_), HeapObject::cast(target));
   }
 }
 
 
 Address RelocInfo::target_reference() {
   ASSERT(rmode_ == EXTERNAL_REFERENCE);
   return Assembler::target_address_at(pc_, host_);
 }
 
 
 Address RelocInfo::target_runtime_entry(Assembler* origin) {
   ASSERT(IsRuntimeEntry(rmode_));
   return target_address();
 }
 
 
 void RelocInfo::set_target_runtime_entry(Address target,
-                                         WriteBarrierMode mode) {
+                                         WriteBarrierMode write_barrier_mode,
+                                         ICacheFlushMode icache_flush_mode) {
   ASSERT(IsRuntimeEntry(rmode_));
-  if (target_address() != target) set_target_address(target, mode);
+  if (target_address() != target)
+    set_target_address(target, write_barrier_mode, icache_flush_mode);
 }
 
 
 Handle<Cell> RelocInfo::target_cell_handle() {
   ASSERT(rmode_ == RelocInfo::CELL);
   Address address = Memory::Address_at(pc_);
   return Handle<Cell>(reinterpret_cast<Cell**>(address));
 }
 
 
 Cell* RelocInfo::target_cell() {
   ASSERT(rmode_ == RelocInfo::CELL);
   return Cell::FromValueAddress(Memory::Address_at(pc_));
 }
 
 
-void RelocInfo::set_target_cell(Cell* cell, WriteBarrierMode mode) {
+void RelocInfo::set_target_cell(Cell* cell,
+                                WriteBarrierMode write_barrier_mode,
+                                ICacheFlushMode icache_flush_mode) {
   ASSERT(rmode_ == RelocInfo::CELL);
   Address address = cell->address() + Cell::kValueOffset;
   Memory::Address_at(pc_) = address;
-  if (mode == UPDATE_WRITE_BARRIER && host() != NULL) {
+  if (write_barrier_mode == UPDATE_WRITE_BARRIER && host() != NULL) {
     // TODO(1550) We are passing NULL as a slot because cell can never be on
     // evacuation candidate.
     host()->GetHeap()->incremental_marking()->RecordWrite(
         host(), NULL, cell);
   }
 }
 
 
 static const int kNoCodeAgeSequenceLength = 3 * Assembler::kInstrSize;
 
@@ skipping 263 matching lines @@
 void Assembler::deserialization_set_special_target_at(
     Address constant_pool_entry, Code* code, Address target) {
   if (FLAG_enable_ool_constant_pool) {
     set_target_address_at(constant_pool_entry, code, target);
   } else {
     Memory::Address_at(constant_pool_entry) = target;
   }
 }
 
 
+static uint32_t ExtractMovwImmediate(Instr instruction) {

[Rodolph Perfetta, 2014/05/19 12:38:38]

the Instruction class has a ImmedMovwMovtValue method which will do this.

[rmcilroy, 2014/05/19 16:52:16]

Ack (no longer applicable).

+  ASSERT(Assembler::IsMovW(instruction) || Assembler::IsMovT(instruction));
+  return ((instruction & 0xf0000) >> 4) | (instruction & 0xfff);
+}
+
+
 static Instr EncodeMovwImmediate(uint32_t immediate) {
   ASSERT(immediate < 0x10000);
   return ((immediate & 0xf000) << 4) | (immediate & 0xfff);
 }
 
 
+static Instr PatchMovwImmediate(Instr instruction, uint32_t immediate) {
+  instruction &= ~EncodeMovwImmediate(0xffff);
+  return instruction | EncodeMovwImmediate(immediate);
+}
+
+
 void Assembler::set_target_address_at(Address pc,
                                       ConstantPoolArray* constant_pool,
-                                      Address target) {
+                                      Address target,
+                                      ICacheFlushMode icache_flush_mode) {
   if (IsMovW(Memory::int32_at(pc))) {
     ASSERT(IsMovT(Memory::int32_at(pc + kInstrSize)));
     uint32_t* instr_ptr = reinterpret_cast<uint32_t*>(pc);
-    uint32_t immediate = reinterpret_cast<uint32_t>(target);
-    uint32_t intermediate = instr_ptr[0];
-    intermediate &= ~EncodeMovwImmediate(0xFFFF);
-    intermediate |= EncodeMovwImmediate(immediate & 0xFFFF);
-    instr_ptr[0] = intermediate;
-    intermediate = instr_ptr[1];
-    intermediate &= ~EncodeMovwImmediate(0xFFFF);
-    intermediate |= EncodeMovwImmediate(immediate >> 16);
-    instr_ptr[1] = intermediate;
+    uint32_t immediate_high = reinterpret_cast<uint32_t>(target) >> 16;
+    uint32_t immediate_low = reinterpret_cast<uint32_t>(target) & 0xFFFF;
+    int instructions_patched = 0;
+    if (ExtractMovwImmediate(instr_ptr[0]) != immediate_low) {
+      instr_ptr[0] = PatchMovwImmediate(instr_ptr[0], immediate_low);
+      instructions_patched++;
+    }
+    if (ExtractMovwImmediate(instr_ptr[1]) != immediate_high) {
+      instr_ptr[1] = PatchMovwImmediate(instr_ptr[1], immediate_high);
+      instructions_patched++;
+    }
     ASSERT(IsMovW(Memory::int32_at(pc)));
     ASSERT(IsMovT(Memory::int32_at(pc + kInstrSize)));
-    CPU::FlushICache(pc, 2 * kInstrSize);
+    if (icache_flush_mode == SKIP_ICACHE_FLUSH ||
+        (icache_flush_mode == SKIP_ICACHE_FLUSH_IF_ATOMIC &&
+         instructions_patched <= 1)) {
+      // We can skip the icache flush in these cases.
+    } else {
+      CPU::FlushICache(pc, 2 * kInstrSize);
+    }
   } else if (FLAG_enable_ool_constant_pool) {
     ASSERT(IsLdrPpImmediateOffset(Memory::int32_at(pc)));
     Memory::Address_at(
       target_constant_pool_address_at(pc, constant_pool)) = target;
   } else {
     ASSERT(IsLdrPcImmediateOffset(Memory::int32_at(pc)));
     Memory::Address_at(target_pointer_address_at(pc)) = target;
     // Intuitively, we would think it is necessary to always flush the
     // instruction cache after patching a target address in the code as follows:
     //   CPU::FlushICache(pc, sizeof(target));
     // However, on ARM, no instruction is actually patched in the case
     // of embedded constants of the form:
     // ldr   ip, [pc, #...]
     // since the instruction accessing this address in the constant pool remains
     // unchanged.
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM_ASSEMBLER_ARM_INL_H_