Implement code sinking.

Small example of what the optimization does:

Object o = new Object();
if (test) {
  throw new Error(o.toString());
}

will be turned into (note that the first user of 'o'
is the 'new Error' allocation which has 'o' in its
environment):
if (test) {
  Object o = new Obect();
  throw new Error(o.toString());
}

There are other examples in 639-checker-code-sinking.

Ritz individual benchmarks improve on art-jit-cc from
5% (EvaluateComplexFormulas) to 23% (MoveFunctionColumn)
on all platforms.

Test: 639-checker-code-sinking
Test: test-art-host
Test: borg job run
Test: libcore + jdwp

bug:35634932
bug:30933338

Change-Id: Ib99c00c93fe76ffffb17afffb5a0e30a14310652

1 files changed, 5 insertions, 1 deletions

diff --git a/compiler/optimizing/common_dominator.h b/compiler/optimizing/common_dominator.h
index b459d24d7c..9f012cfbb2 100644
--- a/compiler/optimizing/common_dominator.h
+++ b/compiler/optimizing/common_dominator.h
@@ -36,12 +36,16 @@ class CommonDominator {
   // Create a finder starting with a given block.
   explicit CommonDominator(HBasicBlock* block)
       : dominator_(block), chain_length_(ChainLength(block)) {
-    DCHECK(block != nullptr);
   }
 
   // Update the common dominator with another block.
   void Update(HBasicBlock* block) {
     DCHECK(block != nullptr);
+    if (dominator_ == nullptr) {
+      dominator_ = block;
+      chain_length_ = ChainLength(block);
+      return;
+    }
     HBasicBlock* block2 = dominator_;
     DCHECK(block2 != nullptr);
     if (block == block2) {