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, 9 insertions, 0 deletions

diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index 0f2c1cffee..ddd39a3898 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -837,6 +837,15 @@ class HBasicBlock : public ArenaObject<kArenaAllocBasicBlock> {
   // blocks are consistent (for example ending with a control flow instruction).
   HBasicBlock* SplitAfter(HInstruction* cursor);
 
+  // Split catch block into two blocks after the original move-exception bytecode
+  // instruction, or at the beginning if not present. Returns the newly created,
+  // latter block, or nullptr if such block could not be created (must be dead
+  // in that case). Note that this method just updates raw block information,
+  // like predecessors, successors, dominators, and instruction list. It does not
+  // update the graph, reverse post order, loop information, nor make sure the
+  // blocks are consistent (for example ending with a control flow instruction).
+  HBasicBlock* SplitCatchBlockAfterMoveException();
+
   // Merge `other` at the end of `this`. Successors and dominated blocks of
   // `other` are changed to be successors and dominated blocks of `this`. Note
   // that this method does not update the graph, reverse post order, loop