ART: Fix simplification of catch blocks in the presence of dead code

Simplification of catch blocks transforms the code so that catch
blocks have only exceptional predecessors. However, it is invoked
before trivially dead code is eliminated which breaks simple
assumptions such as the fact that a catch block cannot start with
move-exception if it has non-exceptional predecessors. This patch
fixes the algorithm to work under these relaxed conditions.

Bug: 25494450
Bug: 25492628
Change-Id: Idc8d010102a4b8b9a6cd918b98d6e11d1838db0c

1 files changed, 4 insertions, 12 deletions

diff --git a/compiler/optimizing/builder.cc b/compiler/optimizing/builder.cc
index ed193c7b61..676e56477e 100644
--- a/compiler/optimizing/builder.cc
+++ b/compiler/optimizing/builder.cc
@@ -359,18 +359,10 @@ void HGraphBuilder::InsertTryBoundaryBlocks(const DexFile::CodeItem& code_item)
           // need a strategy for splitting exceptional edges. We split the block
           // after the move-exception (if present) and mark the first part not
           // throwing. The normal-flow edge between them will be split later.
-          HInstruction* first_insn = block->GetFirstInstruction();
-          if (first_insn->IsLoadException()) {
-            // Catch block starts with a LoadException. Split the block after
-            // the StoreLocal and ClearException which must come after the load.
-            DCHECK(first_insn->GetNext()->IsStoreLocal());
-            DCHECK(first_insn->GetNext()->GetNext()->IsClearException());
-            throwing_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.
-            throwing_block = block->SplitBefore(first_insn);
-          }
+          throwing_block = block->SplitCatchBlockAfterMoveException();
+          // Move-exception does not throw and the block has throwing insructions
+          // so it must have been possible to split it.
+          DCHECK(throwing_block != nullptr);
         }
 
         try_block_info.Put(throwing_block->GetBlockId(),