Cleanup the ARM code generator for try...catch and try...finally by...

src/codegen-arm.cc

 // Copyright 2006-2008 the V8 project authors. 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.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1746 matching lines @@
   // label.
   int nof_escapes = node->escaping_labels()->length();
   List<LabelShadow*> shadows(1 + nof_escapes);
   shadows.Add(new LabelShadow(&function_return_));
   for (int i = 0; i < nof_escapes; i++) {
     shadows.Add(new LabelShadow(node->escaping_labels()->at(i)));
   }
 
   // Generate code for the statements in the try block.
   VisitStatements(node->try_block()->statements());
-  frame_->Pop();  // Discard the result.
+  // Discard the code slot from the handler.
+  frame_->Pop();
 
   // Stop the introduced shadowing and count the number of required unlinks.
   // After shadowing stops, the original labels are unshadowed and the
   // LabelShadows represent the formerly shadowing labels.
   int nof_unlinks = 0;
   for (int i = 0; i <= nof_escapes; i++) {
     shadows[i]->StopShadowing();
     if (shadows[i]->is_linked()) nof_unlinks++;
   }
 
   // Unlink from try chain.
-  // TOS contains code slot
-  const int kNextIndex = (StackHandlerConstants::kNextOffset
-                          + StackHandlerConstants::kAddressDisplacement)
-                       / kPointerSize;
+  // The code slot has already been discarded, so the next index is
+  // adjusted by 1.
+  const int kNextIndex =
+      (StackHandlerConstants::kNextOffset / kPointerSize) - 1;
   __ ldr(r1, frame_->Element(kNextIndex));  // read next_sp
   __ mov(r3, Operand(ExternalReference(Top::k_handler_address)));
   __ str(r1, MemOperand(r3));
-  ASSERT(StackHandlerConstants::kCodeOffset == 0);  // first field is code
+  // The code slot has already been dropped from the handler.
   frame_->Drop(StackHandlerConstants::kSize / kPointerSize - 1);
-  // Code slot popped.
   if (nof_unlinks > 0) __ b(&exit);
 
   // Generate unlink code for the (formerly) shadowing labels that have been
   // jumped to.
   for (int i = 0; i <= nof_escapes; i++) {
     if (shadows[i]->is_linked()) {
       // Unlink from try chain;
       __ bind(shadows[i]);
 
       // Reload sp from the top handler, because some statements that we
       // break from (eg, for...in) may have left stuff on the stack.
       __ mov(r3, Operand(ExternalReference(Top::k_handler_address)));
       __ ldr(sp, MemOperand(r3));
 
       __ ldr(r1, frame_->Element(kNextIndex));
       __ str(r1, MemOperand(r3));
-      ASSERT(StackHandlerConstants::kCodeOffset == 0);  // first field is code
+      // The code slot has already been dropped from the handler.
       frame_->Drop(StackHandlerConstants::kSize / kPointerSize - 1);
-      // Code slot popped.
 
       __ b(shadows[i]->original_label());
     }
   }
 
   __ bind(&exit);
 }
 
 
 void CodeGenerator::VisitTryFinally(TryFinally* node) {
@@ skipping 66 matching lines @@
         frame_->Push(r0);
       }
       __ mov(r2, Operand(Smi::FromInt(JUMPING + i)));
       __ b(&unlink);
     }
   }
 
   // Unlink from try chain;
   __ bind(&unlink);
 
-  frame_->Pop(r0);  // Store TOS in r0 across stack manipulation
+  frame_->Pop(r0);  // Preserve TOS result in r0 across stack manipulation.
   // Reload sp from the top handler, because some statements that we
   // break from (eg, for...in) may have left stuff on the stack.
   __ mov(r3, Operand(ExternalReference(Top::k_handler_address)));
   __ ldr(sp, MemOperand(r3));
   const int kNextIndex = (StackHandlerConstants::kNextOffset
                           + StackHandlerConstants::kAddressDisplacement)
                        / kPointerSize;
   __ ldr(r1, frame_->Element(kNextIndex));
   __ str(r1, MemOperand(r3));
   ASSERT(StackHandlerConstants::kCodeOffset == 0);  // first field is code
+  // The stack pointer was restored to just below the code slot (the
+  // topmost slot) of the handler, so all but the code slot need to be
+  // dropped.
   frame_->Drop(StackHandlerConstants::kSize / kPointerSize - 1);
-  // Code slot popped.
+  // Restore result to TOS.
   frame_->Push(r0);
 
   // --- Finally block ---
   __ bind(&finally_block);
 
   // Push the state on the stack.
   frame_->Push(r2);
 
   // We keep two elements on the stack - the (possibly faked) result
   // and the state - while evaluating the finally block. Record it, so
   // that a break/continue crossing this statement can restore the
   // stack.
   const int kFinallyStackSize = 2 * kPointerSize;
   break_stack_height_ += kFinallyStackSize;
 
   // Generate code for the statements in the finally block.
   VisitStatements(node->finally_block()->statements());
 
   // Restore state and return value or faked TOS.
   frame_->Pop(r2);
   frame_->Pop(r0);
   break_stack_height_ -= kFinallyStackSize;
 
   // Generate code to jump to the right destination for all used (formerly)
   // shadowing labels.
   for (int i = 0; i <= nof_escapes; i++) {
     if (shadows[i]->is_bound()) {
       __ cmp(r2, Operand(Smi::FromInt(JUMPING + i)));
-      if (shadows[i]->original_label() != &function_return_) {
-        Label next;
-        __ b(ne, &next);
-        __ b(shadows[i]->original_label());
-        __ bind(&next);
-      } else {
-        __ b(eq, shadows[i]->original_label());
-      }
+      __ b(eq, shadows[i]->original_label());
     }
   }
 
   // Check if we need to rethrow the exception.
   __ cmp(r2, Operand(Smi::FromInt(THROWING)));
   __ b(ne, &exit);
 
   // Rethrow exception.
   frame_->Push(r0);
   __ CallRuntime(Runtime::kReThrow, 1);
@@ skipping 2505 matching lines @@
   __ mov(r2, Operand(0));
   __ GetBuiltinEntry(r3, Builtins::CALL_NON_FUNCTION);
   __ Jump(Handle<Code>(Builtins::builtin(Builtins::ArgumentsAdaptorTrampoline)),
           RelocInfo::CODE_TARGET);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal