Remove tries which don't contain throwing instructions

If nothing can throw within a TryBoundary, we are safe to eliminate
it. We were already doing this at the builder stage, but this CL
takes care of subsequent passes (e.g. we might remove DivZeroCheck
instructions which means that now we know we can't throw).

Sometimes this means we are able to eliminate catch blocks which
brings some code size improvements.

Locally on a Pixel 5 compiling with `speed`:
 * AGSA -684K (0.2%)
 * services.jar -100K (0.2%)
 * SystemUIGoogle -88K (0.3%)

Bug: 229249867
Test: art/test/testrunner/testrunner.py --host --64 --optimizing -b
Change-Id: I36d5880be99c1f1109c94266b1be583de8d6cf72

1 files changed, 20 insertions, 0 deletions

diff --git a/compiler/optimizing/dead_code_elimination.h b/compiler/optimizing/dead_code_elimination.h
index a3e993c1d7..873e13f244 100644
--- a/compiler/optimizing/dead_code_elimination.h
+++ b/compiler/optimizing/dead_code_elimination.h
@@ -46,6 +46,26 @@ class HDeadCodeElimination : public HOptimization {
   bool SimplifyIfs();
   void ConnectSuccessiveBlocks();
 
+  // Helper struct to eliminate tries.
+  struct TryBelongingInformation;
+  // Disconnects `block`'s handlers and update its `TryBoundary` instruction to a `Goto`.
+  // Sets `any_handler_in_loop` to true if any handler is currently a loop to later update the loop
+  // information if needed.
+  void DisconnectHandlersAndUpdateTryBoundary(HBasicBlock* block,
+                                              /* out */ bool* any_handler_in_loop);
+  // Returns true iff the try doesn't contain throwing instructions.
+  bool CanPerformTryRemoval(const TryBelongingInformation& try_belonging_info);
+  // Removes the try by disconnecting all try entries and exits from their handlers. Also updates
+  // the graph in the case that a `TryBoundary` instruction of kind `exit` has the Exit block as
+  // its successor.
+  void RemoveTry(HBasicBlock* try_entry,
+                 const TryBelongingInformation& try_belonging_info,
+                 bool* any_catch_in_loop);
+  // Checks which tries (if any) are currently in the graph, coalesces the different try entries
+  // that are referencing the same try, and removes the tries which don't contain any throwing
+  // instructions.
+  bool RemoveUnneededTries();
+
   DISALLOW_COPY_AND_ASSIGN(HDeadCodeElimination);
 };