ART: Move exception clearing into own instruction

Runtime delivers exceptions only to catch blocks which begin with a
MOVE_EXCEPTION instruction (in DEX). In that case, the catch block is
expected to clear the thread-local exception storage after having
read the exception reference.

This patch changes Optimizing to represent MOVE_EXCEPTION with two
instructions - HLoadException and HClearException - instead of one.
If the exception reference is not used, HLoadException can be safely
removed, saving a memory load without breaking the runtime behaviour.

Change-Id: Idad8a714467bf9d9d5fccefbc43c0bd8ae13ddba

1 files changed, 4 insertions, 2 deletions

diff --git a/compiler/optimizing/builder.cc b/compiler/optimizing/builder.cc
index 52a3a1534a..88414980b8 100644
--- a/compiler/optimizing/builder.cc
+++ b/compiler/optimizing/builder.cc
@@ -357,9 +357,10 @@ void HGraphBuilder::InsertTryBoundaryBlocks(const DexFile::CodeItem& code_item)
         HInstruction* first_insn = block->GetFirstInstruction();
         if (first_insn->IsLoadException()) {
           // Catch block starts with a LoadException. Split the block after the
-          // StoreLocal that must come after the load.
+          // StoreLocal and ClearException which must come after the load.
           DCHECK(first_insn->GetNext()->IsStoreLocal());
-          block = block->SplitBefore(first_insn->GetNext()->GetNext());
+          DCHECK(first_insn->GetNext()->GetNext()->IsClearException());
+          block = block->SplitBefore(first_insn->GetNext()->GetNext()->GetNext());
         } else {
           // Catch block does not load the exception. Split at the beginning to
           // create an empty catch block.
@@ -2552,6 +2553,7 @@ bool HGraphBuilder::AnalyzeDexInstruction(const Instruction& instruction, uint32
     case Instruction::MOVE_EXCEPTION: {
       current_block_->AddInstruction(new (arena_) HLoadException());
       UpdateLocal(instruction.VRegA_11x(), current_block_->GetLastInstruction());
+      current_block_->AddInstruction(new (arena_) HClearException());
       break;
     }