Add PC descriptor for ret instruction

runtime/vm/code_generator_ia32.cc

Index: runtime/vm/code_generator_ia32.cc
===================================================================
--- runtime/vm/code_generator_ia32.cc	(revision 4139)
+++ runtime/vm/code_generator_ia32.cc	(working copy)
@@ -757,7 +757,7 @@
 }
 
 
-void CodeGenerator::GenerateReturnEpilog() {
+void CodeGenerator::GenerateReturnEpilog(ReturnNode* node) {
   // Unchain the context(s) up to context level 0.
   int context_level = state()->context_level();
   ASSERT(context_level >= 0);
@@ -788,6 +788,12 @@
   }
   __ LeaveFrame();
   __ ret();
+  // Add a NOP to make return code pattern 5 bytes long for patching
+  // in breakpoints during debugging.

[srdjan, 2012/02/11 11:58:50]

Since we do not execute this code, would it make sense to add int3 instead?

[hausner, 2012/02/13 17:27:10]

If it isn't executed, it seems irrelevant whether it's NOP ir INT3. the nop
documents that it has no function other than take up space.

+  __ nop(1);
+  AddCurrentDescriptor(PcDescriptors::kReturn,
+                       AstNode::kNoId,

[srdjan, 2012/02/11 11:58:50]

Why not use return node id?

[hausner, 2012/02/13 17:27:10]

No particular reason. Will do in next change.

+                       node->token_index());
 
 #ifdef DEBUG
   __ Bind(&wrong_stack);
@@ -837,7 +843,7 @@
           String::ZoneHandle(String::NewSymbol("function result")));
     }
   }
-  GenerateReturnEpilog();
+  GenerateReturnEpilog(node);
 }