Optimise the deoptimisation check to improve performance on modern ARM cores.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org//7021007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7909 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/lithium-codegen-arm.cc

@@ -85,6 +85,7 @@ bool LCodeGen::GenerateCode() {
   return GeneratePrologue() &&
       GenerateBody() &&
       GenerateDeferredCode() &&
+      GenerateDeoptJumpTable() &&
       GenerateSafepointTable();
 }
 
@@ -249,13 +250,41 @@ bool LCodeGen::GenerateDeferredCode() {
     __ jmp(code->exit());
   }
 
-  // Force constant pool emission at the end of deferred code to make
+  return !is_aborted();
+}
+
+
+bool LCodeGen::GenerateDeoptJumpTable() {
+  // Check that the jump table is accessible from everywhere in the function
+  // code, ie that offsets to the table can be encoded in the 24bit signed
+  // immediate of a branch instruction.
+  // To simplify we consider the code size from the first instruction to the
+  // end of the jump table. We also don't consider the pc load delta.
+  // Each entry in the jump table generates only one instruction.
+  if (!is_int24((masm()->pc_offset() / Assembler::kInstrSize) +
+      deopt_jump_table_.length())) {
+    Abort("Generated code is too large");
+  }
+
+  __ RecordComment("[ Deoptimisation jump table");
+  Label table_start;
+  __ bind(&table_start);
+  for (int i = 0; i < deopt_jump_table_.length(); i++) {
+    __ bind(&deopt_jump_table_[i].label);
+    __ mov(pc, Operand(reinterpret_cast<int32_t>(deopt_jump_table_[i].address),
+                       RelocInfo::RUNTIME_ENTRY));
+  }
+  ASSERT(masm()->InstructionsGeneratedSince(&table_start) ==
+      deopt_jump_table_.length());
+  __ RecordComment("]");
+
+  // Force constant pool emission at the end of the jump table to make
   // sure that no constant pools are emitted after the official end of
   // the instruction sequence.
   masm()->CheckConstPool(true, false);
 
-  // Deferred code is the last part of the instruction sequence. Mark
-  // the generated code as done unless we bailed out.
+  // The deoptimization jump table is the last part of the instruction
+  // sequence. Mark the generated code as done unless we bailed out.
   if (!is_aborted()) status_ = DONE;
   return !is_aborted();
 }
@@ -595,19 +624,18 @@ void LCodeGen::DeoptimizeIf(Condition cc, LEnvironment* environment) {
     return;
   }
 
+  if (FLAG_trap_on_deopt) __ stop("trap_on_deopt", cc);
+
   if (cc == al) {
-    if (FLAG_trap_on_deopt) __ stop("trap_on_deopt");
     __ Jump(entry, RelocInfo::RUNTIME_ENTRY);
   } else {
-    if (FLAG_trap_on_deopt) {
-      Label done;
-      __ b(&done, NegateCondition(cc));
-      __ stop("trap_on_deopt");
-      __ Jump(entry, RelocInfo::RUNTIME_ENTRY);
-      __ bind(&done);
-    } else {
-      __ Jump(entry, RelocInfo::RUNTIME_ENTRY, cc);
+    // We often have several deopts to the same entry, reuse the last
+    // jump entry if this is the case.
+    if (deopt_jump_table_.is_empty() ||
+        (deopt_jump_table_.last().address != entry)) {
+      deopt_jump_table_.Add(JumpTableEntry(entry));
     }
+    __ b(cc, &deopt_jump_table_.last().label);
   }
 }
 

src/arm/lithium-codegen-arm.h

@@ -51,6 +51,7 @@ class LCodeGen BASE_EMBEDDED {
         current_instruction_(-1),
         instructions_(chunk->instructions()),
         deoptimizations_(4),
+        deopt_jump_table_(4),
         deoptimization_literals_(8),
         inlined_function_count_(0),
         scope_(info->scope()),
@@ -172,6 +173,7 @@ class LCodeGen BASE_EMBEDDED {
   bool GeneratePrologue();
   bool GenerateBody();
   bool GenerateDeferredCode();
+  bool GenerateDeoptJumpTable();
   bool GenerateSafepointTable();
 
   enum SafepointMode {
@@ -289,6 +291,14 @@ class LCodeGen BASE_EMBEDDED {
                                        Handle<Map> type,
                                        Handle<String> name);
 
+  struct JumpTableEntry {
+    explicit inline JumpTableEntry(Address entry)
+        : label(),
+          address(entry) { }
+    Label label;
+    Address address;
+  };
+
   LChunk* const chunk_;
   MacroAssembler* const masm_;
   CompilationInfo* const info_;
@@ -297,6 +307,7 @@ class LCodeGen BASE_EMBEDDED {
   int current_instruction_;
   const ZoneList<LInstruction*>* instructions_;
   ZoneList<LEnvironment*> deoptimizations_;
+  ZoneList<JumpTableEntry> deopt_jump_table_;
   ZoneList<Handle<Object> > deoptimization_literals_;
   int inlined_function_count_;
   Scope* const scope_;