Add flags for write barrier elimination and local allocation folding.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/166163003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19382 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/flag-definitions.h

@@ -254,6 +254,9 @@ DEFINE_bool(use_canonicalizing, true, "use hydrogen instruction canonicalizing")
 DEFINE_bool(use_inlining, true, "use function inlining")
 DEFINE_bool(use_escape_analysis, true, "use hydrogen escape analysis")
 DEFINE_bool(use_allocation_folding, true, "use allocation folding")
+DEFINE_bool(use_local_allocation_folding, false, "only fold in basic blocks")
+DEFINE_bool(use_write_barrier_elimination, true,
+            "eliminate write barriers targeting allocations in optimized code")
 DEFINE_int(max_inlining_levels, 5, "maximum number of inlining levels")
 DEFINE_int(max_inlined_source_size, 600,
            "maximum source size in bytes considered for a single inlining")

src/hydrogen-instructions.cc

@@ -3438,6 +3438,15 @@ bool HAllocate::HandleSideEffectDominator(GVNFlag side_effect,
     return false;
   }
 
+  // Check whether we are folding within the same block for local folding.
+  if (FLAG_use_local_allocation_folding && dominator->block() != block()) {
+    if (FLAG_trace_allocation_folding) {
+      PrintF("#%d (%s) cannot fold into #%d (%s), crosses basic blocks\n",
+          id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
+    }
+    return false;
+  }
+
   HAllocate* dominator_allocate = HAllocate::cast(dominator);
   HValue* dominator_size = dominator_allocate->size();
   HValue* current_size = size();

src/hydrogen-instructions.h

@@ -6528,6 +6528,7 @@ class HStoreNamedField V8_FINAL : public HTemplateInstruction<3> {
   virtual bool HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator) V8_OVERRIDE {
     ASSERT(side_effect == kNewSpacePromotion);
+    if (!FLAG_use_write_barrier_elimination) return false;
     new_space_dominator_ = dominator;
     return false;
   }