Improve and simplify removal of unreachable code

src/hydrogen-mark-unreachable.cc

Index: src/hydrogen-mark-unreachable.cc
diff --git a/src/hydrogen-infer-types.cc b/src/hydrogen-mark-unreachable.cc
similarity index 53%
copy from src/hydrogen-infer-types.cc
copy to src/hydrogen-mark-unreachable.cc
index 01c608473672f0e3bdfc507b2c8a03526242983f..73123b325763639f5e4b7b7a0305ff2d4abf39e5 100644
--- a/src/hydrogen-infer-types.cc
+++ b/src/hydrogen-mark-unreachable.cc
@@ -25,53 +25,54 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-#include "hydrogen-infer-types.h"
+#include "hydrogen-mark-unreachable.h"
 
 namespace v8 {
 namespace internal {
 
-void HInferTypesPhase::InferTypes(int from_inclusive, int to_inclusive) {
-  for (int i = from_inclusive; i <= to_inclusive; ++i) {
-    HBasicBlock* block = graph()->blocks()->at(i);
 
-    const ZoneList<HPhi*>* phis = block->phis();
-    for (int j = 0; j < phis->length(); j++) {
-      phis->at(j)->UpdateInferredType();
-    }
-
-    for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
-      it.Current()->UpdateInferredType();
-    }
-
-    if (block->IsLoopHeader()) {
-      HBasicBlock* last_back_edge =
-          block->loop_information()->GetLastBackEdge();
-      InferTypes(i + 1, last_back_edge->block_id());
-      // Skip all blocks already processed by the recursive call.
-      i = last_back_edge->block_id();
-      // Update phis of the loop header now after the whole loop body is
-      // guaranteed to be processed.
-      for (int j = 0; j < block->phis()->length(); ++j) {
-        HPhi* phi = block->phis()->at(j);
-        worklist_.Add(phi, zone());
-        in_worklist_.Add(phi->id());
-      }
-      while (!worklist_.is_empty()) {
-        HValue* current = worklist_.RemoveLast();
-        in_worklist_.Remove(current->id());
-        if (current->UpdateInferredType()) {
-          for (HUseIterator it(current->uses()); !it.Done(); it.Advance()) {
-            HValue* use = it.value();
-            if (!in_worklist_.Contains(use->id())) {
-              in_worklist_.Add(use->id());
-              worklist_.Add(use, zone());
+void HMarkUnreachableBlocksPhase::MarkUnreachableBlocks() {
+  // If there is unreachable code in the graph, propagate the unreachable marks
+  // using a fixed-point iteration.
+  bool changed = true;
+  const ZoneList<HBasicBlock*>* blocks = graph()->blocks();
+  while (changed) {
+    changed = false;
+    for (int i = 0; i < blocks->length(); i++) {
+      HBasicBlock* block = blocks->at(i);
+      if (block->IsReachable()) {

[Jakob Kummerow, 2013/10/01 11:59:20]

nit: you can avoid one level of indentation by turning this into an early
return:
      if (block->IsUnreachable()) continue;

[danno, 2013/10/23 11:46:51]

Done.

+        bool is_reachable = blocks->at(0) == block;
+        for (HPredecessorIterator it(block); !it.Done(); it.Advance()) {
+          HBasicBlock* predecessor = it.Current();
+          // A block is reachable if one of it's predecessor is reachable,

[Jakob Kummerow, 2013/10/01 17:47:13]

nit: s/it's predecessor/its predecessors/

[danno, 2013/10/23 11:46:51]

Done.

+          // doesn't deoptimize and either is known to transfer control to the
+          // block or has a control flow instruction for which the next block
+          // cannot be determined.
+          if (predecessor->IsReachable() && !predecessor->IsDeoptimizing()) {
+            HBasicBlock* pred_succ;
+            bool known_pred_succ =
+                predecessor->end()->KnownSuccessorBlock(&pred_succ);
+            if (!known_pred_succ || pred_succ == block) {
+              is_reachable = true;
+              break;
             }
           }
+          if (block->is_osr_entry()) {
+            is_reachable = true;
+          }
+        }
+        if (!is_reachable) {
+          block->MarkUnreachable();
+          changed = true;
         }
       }
-      ASSERT(in_worklist_.IsEmpty());
     }
   }
 }
 
+
+void HMarkUnreachableBlocksPhase::Run() {
+  MarkUnreachableBlocks();
+}
+
 } }  // namespace v8::internal