Added optimization for div/mod by constant power of 2.

src/ia32/codegen-ia32.cc

Index: src/ia32/codegen-ia32.cc
diff --git a/src/ia32/codegen-ia32.cc b/src/ia32/codegen-ia32.cc
index 9fe67587abd1ba3688a5490f2c75560af5c0a2e2..ab08ac35aebd27585848146aba082577a53560cf 100644
--- a/src/ia32/codegen-ia32.cc
+++ b/src/ia32/codegen-ia32.cc
@@ -1848,6 +1848,39 @@ Result CodeGenerator::ConstantSmiBinaryOperation(Token::Value op,
       break;
     }
 
+    case Token::DIV:
+      if (!reversed && int_value == 2) {
+        operand->ToRegister();
+        frame_->Spill(operand->reg());

[William Hesse, 2010/05/10 14:10:43]

If we know that we are in a to-int32 context, where the result will be converted
to int32, then we should be able to handle odd numbers divided by 2!

+
+        DeferredInlineSmiOperation* deferred =
+            new DeferredInlineSmiOperation(op,
+                                           operand->reg(),
+                                           operand->reg(),
+                                           smi_value,
+                                           overwrite_mode);
+        // Check that lowest log2(value) bits of operand are zero, and test
+        // smi tag at the same time.
+        ASSERT_EQ(0, kSmiTag);
+        ASSERT_EQ(1, kSmiTagSize);
+        __ test(operand->reg(), Immediate(3));
+        deferred->Branch(not_zero);  // Branch if non-smi or odd smi.
+        __ sar(operand->reg(), 1);
+        deferred->BindExit();
+        answer = *operand;
+      } else {
+        // Cannot fall through MOD to default case, so we duplicate the
+        // default case here.
+        Result constant_operand(value);
+        if (reversed) {
+          answer = LikelySmiBinaryOperation(op, &constant_operand, operand,
+                                            overwrite_mode);
+        } else {
+          answer = LikelySmiBinaryOperation(op, operand, &constant_operand,
+                                            overwrite_mode);
+        }
+      }
+      break;
     // Generate inline code for mod of powers of 2 and negative powers of 2.
     case Token::MOD:
       if (!reversed &&