Patch to enhance the source code line information for profiler.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
===================================================================
--- src/arm/lithium-codegen-arm.cc	(revision 15993)
+++ src/arm/lithium-codegen-arm.cc	(working copy)
@@ -256,6 +256,7 @@
 bool LCodeGen::GenerateBody() {
   ASSERT(is_generating());
   bool emit_instructions = true;
+  int old_position = RelocInfo::kNoPosition;
   for (current_instruction_ = 0;
        !is_aborted() && current_instruction_ < instructions_->length();
        current_instruction_++) {
@@ -274,6 +275,12 @@
               instr->Mnemonic());
     }
 
+    int pos = instr->position();
+    if (pos >= 0 && pos != old_position) {
+      RecordPosition(pos);
+      old_position = pos;
+    }
+
     instr->CompileToNative(this);
   }
   EnsureSpaceForLazyDeopt();
@@ -287,6 +294,10 @@
   if (deferred_.length() > 0) {
     for (int i = 0; !is_aborted() && i < deferred_.length(); i++) {
       LDeferredCode* code = deferred_[i];
+
+      int pos = instructions_->at(code->instruction_index())->position();
+      if (pos >=0) RecordPosition(pos);

[danno, 2013/08/02 10:53:16]

Since code is ouput linearly, I think it makes sense to have a old_position
member on the codegen object and a method RecordAndUpdatePosition(pos) that has
the logic that encapsulates the logic for eliding repeating positions, and call
that thing here and above. Same applies to other platforms.

+
       Comment(";;; <@%d,#%d> "
               "-------------------- Deferred %s --------------------",
               code->instruction_index(),