Skip some conditional deopts for Div/Mul when all uses are truncating

src/hydrogen.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2076 matching lines @@
         instr != NULL;
         instr = instr->next()) {
       instr->FinalizeUniqueValueId();
     }
   }
 }
 
 
 void HGraph::Canonicalize() {
   HPhase phase("H_Canonicalize", this);
+  // Before removing no-op instructions, save their semantic value.
+  // We must be careful not to set the flag unnecessarily, because GVN
+  // cannot identify two instructions when their flag value differs.
   for (int i = 0; i < blocks()->length(); ++i) {
     HInstruction* instr = blocks()->at(i)->first();
     while (instr != NULL) {
+      if (instr->IsArithmeticBinaryOperation() &&
+          instr->representation().IsInteger32() &&
+          instr->HasAtLeastOneUseWithFlagAndNoneWithout(
+              HInstruction::kTruncatingToInt32)) {
+        instr->SetFlag(HInstruction::kAllUsesTruncatingToInt32);
+      }
+      instr = instr->next();
+    }
+  }
+  // Perform actual Canonicalization pass.
+  for (int i = 0; i < blocks()->length(); ++i) {
+    HInstruction* instr = blocks()->at(i)->first();
+    while (instr != NULL) {
       HValue* value = instr->Canonicalize();
       if (value != instr) instr->DeleteAndReplaceWith(value);
       instr = instr->next();
     }
   }
 }
 
 // Block ordering was implemented with two mutually recursive methods,
 // HGraph::Postorder and HGraph::PostorderLoopBlocks.
 // The recursion could lead to stack overflow so the algorithm has been
@@ skipping 9490 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal