ARM: make MacroAssembler::LoadRoot emit exactly one instruction when in...

ARM: make MacroAssembler::LoadRoot emit exactly one instruction when in predictable code size scope.

BUG=v8:2439
R=danno@chromium.org

Review URL: https://chromiumcodereview.appspot.com/11280276

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13113 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/codegen-arm.cc

@@ -606,6 +606,7 @@ static byte* GetNoCodeAgeSequence(uint32_t* length) {
   *length = kNoCodeAgeSequenceLength * Assembler::kInstrSize;
   if (!initialized) {
     CodePatcher patcher(byte_sequence, kNoCodeAgeSequenceLength);
+    PredictableCodeSizeScope scope(patcher.masm(), *length);
     patcher.masm()->stm(db_w, sp, r1.bit() | cp.bit() | fp.bit() | lr.bit());
     patcher.masm()->LoadRoot(ip, Heap::kUndefinedValueRootIndex);
     patcher.masm()->add(fp, sp, Operand(2 * kPointerSize));

src/arm/full-codegen-arm.cc

@@ -165,14 +165,18 @@ void FullCodeGenerator::Generate() {
   int locals_count = info->scope()->num_stack_slots();
 
   info->set_prologue_offset(masm_->pc_offset());
-  // The following four instructions must remain together and unmodified for
-  // code aging to work properly.
+  {
+    PredictableCodeSizeScope predictible_code_size_scope(
+        masm_, kNoCodeAgeSequenceLength * Assembler::kInstrSize);
+    // The following three instructions must remain together and unmodified
+    // for code aging to work properly.
     __ stm(db_w, sp, r1.bit() | cp.bit() | fp.bit() | lr.bit());
     // Load undefined value here, so the value is ready for the loop
     // below.
     __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
-  // Adjust fp to point to caller's fp.
+    // Adjust FP to point to saved FP.
     __ add(fp, sp, Operand(2 * kPointerSize));
+  }
 
   { Comment cmnt(masm_, "[ Allocate locals");
     for (int i = 0; i < locals_count; i++) {

src/arm/lithium-codegen-arm.cc

@@ -148,13 +148,18 @@ bool LCodeGen::GeneratePrologue() {
 
 
   info()->set_prologue_offset(masm_->pc_offset());
-  // The following three instructions must remain together and unmodified for
-  // code aging to work properly.
+  {
+    PredictableCodeSizeScope predictible_code_size_scope(
+        masm_, kNoCodeAgeSequenceLength * Assembler::kInstrSize);
+    // The following three instructions must remain together and unmodified
+    // for code aging to work properly.
     __ stm(db_w, sp, r1.bit() | cp.bit() | fp.bit() | lr.bit());
-  // Add unused load of ip to ensure prologue sequence is identical for
-  // full-codegen and lithium-codegen.
+    // Load undefined value here, so the value is ready for the loop
+    // below.
     __ LoadRoot(ip, Heap::kUndefinedValueRootIndex);
-  __ add(fp, sp, Operand(2 * kPointerSize));  // Adjust FP to point to saved FP.
+    // Adjust FP to point to saved FP.
+    __ add(fp, sp, Operand(2 * kPointerSize));
+  }
 
   // Reserve space for the stack slots needed by the code.
   int slots = GetStackSlotCount();

src/arm/macro-assembler-arm.cc

@@ -423,7 +423,8 @@ void MacroAssembler::LoadRoot(Register destination,
                               Heap::RootListIndex index,
                               Condition cond) {
   if (CpuFeatures::IsSupported(MOVW_MOVT_IMMEDIATE_LOADS) &&
-      !Heap::RootCanBeWrittenAfterInitialization(index)) {
+      !Heap::RootCanBeWrittenAfterInitialization(index) &&
+      !predictable_code_size()) {
     Handle<Object> root(isolate()->heap()->roots_array_start()[index]);
     if (!isolate()->heap()->InNewSpace(*root)) {
       // The CPU supports fast immediate values, and this root will never