Coalesce Return/ReturnVoid instructions

We do this to avoid generating the exit frame code several times.

We don't create new Return/ReturnVoid instructions after the
inliner, and CodeSinking looks like a logical place to add this
optimization.

Locally, speed-compiling in Pixel 5:
 * system server: -516.05KB (1.1%)
 * SystemUIGoogle: -216.50KB (0.8%)
 * AGSA: -3021.91KB (0.93%)

Bug: 203237752
Bug: 188926997
Bug: 194133637
Test: art/test/testrunner/testrunner.py --host --64 --optimizing -b
Change-Id: Ib149382462efac82a0bbc114cbdbc773e1a5228c

1 files changed, 7 insertions, 1 deletions

diff --git a/compiler/optimizing/code_sinking.h b/compiler/optimizing/code_sinking.h
index 14f62f2417..c743db40d9 100644
--- a/compiler/optimizing/code_sinking.h
+++ b/compiler/optimizing/code_sinking.h
@@ -39,10 +39,16 @@ class CodeSinking : public HOptimization {
   static constexpr const char* kCodeSinkingPassName = "code_sinking";
 
  private:
-  // Try to move code only used by `end_block` and all its post-dominated / dominated
+  // Tries to sink code to uncommon branches.
+  void UncommonBranchSinking();
+  // Tries to move code only used by `end_block` and all its post-dominated / dominated
   // blocks, to these blocks.
   void SinkCodeToUncommonBranch(HBasicBlock* end_block);
 
+  // Coalesces the Return/ReturnVoid instructions into one, if we have two or more. We do this to
+  // avoid generating the exit frame code several times.
+  void ReturnSinking();
+
   DISALLOW_COPY_AND_ASSIGN(CodeSinking);
 };